View Full Version : TDC Offset exposed - or, who knows what evil lurks in the hearts and minds of men?
da Shadow do....
DS4 Electronic Fuel Injection factory Base timing is manually set to +3.5deg (advanced with respect to crankshaft Top Dead Center for cylinder #1), with TDC Offset at -0.5deg, which is retarded, and is a value the PCM controls.
Seems kinda stupid, right, advancing the Inj Pump to try to squeeze 195hp outta this thing, then letting the PCM take some of it away?
Well - gather around kiddies, for a tale of deception and struggle in a quest for power and control.
The DS4 Inj Pump is precisely designed, and factory adjusment is only required for 0.005" Fuel Solenoid travel, and Optic Sensor position on camring, (and some other stuff, which is not pertinent to this tale).
Camring, which creates pumping action for the rollers and pump plungers, is precisely marked for Top Dead Center with respect to Inj Pump internal mechanical timing.
Camring ramps, where pump plunger rollers ride, consist of 6 distinct areas -
valley - where no pumping action occurs
lead-in - for smooth roller action onto ramp
initial ramp - where FS closes, pressure begins increasing
secondary ramp - very aggressive, with high rate of pressure increase
peak - point, and end, of maximum pressure
down ramp - smoothly transits rollers to valley, for next cylinder pressure cycle.
Inj Pump is high precision, such that installation on any engine only requires Time Set routine - TDC Offset adjustment is not required, if new IP is adjusted to engine's timing with previous IP, according to some manuals.
DS4 injection is of the constant-beginning, variable-ending type, with respect to the camring.
Initial pump timing or required electronic advance does not change the point on the camring where injection pressure starts increasing - this is the mechanical start of the injection cycle.
PCM control of Fuel Solenoid begins the electronic injection cycle, and can vary ending of injection, allowing for variable Fuel Rate for varying loads.
Factory adjustment of Optic Sensor to camring TDC allows an injection rate of pressure increase which is suitable for +3.5deg Base IP timing.
This gives minimum wear on IP internals and injectors, for maximum service life, also restricting engine power output, which is a function of thermal throughput and dissipation.
'Nother words - the 6.5 overheats rapidly when stoked.
A procedure has been done, where the Optic Sensor is mechanically retarded on the camring, by about -1.5 to -1.94deg. (those numbers seem familiar to anyone?)
At start-up, PCM 'sees' the OS as retarded, promptly calling for advance necessary to bring it back into it's correct timing position..
PCM does not know, however, that the camring is now +1.50 to +1.94deg advanced, so when it's electronic injection cycle is initiated, the agressive ramp on the camring has been moved closer to the rollers, pump pressure is much higher and increasing more rapidly, injectors 'pop' sooner, and we get the familiar increased crispness of injection and a little noisier combustion rattle.
As this procedure has mostly been done without Base timing adjust, only minimal power increase is accomplished, but an increase, nevertheless.
Now, lets work WITH the PCM on this.
Again, factory Base timing is manually set to +3.5deg (advanced with respect to crankshaft Top Dead Center for cylinder #1), with TDC Offset at -0.5deg, which is retarded, is a value the PCM controls.
Also again, seems kinda stupid, right, advancing the Inj Pump to get 195hp, then letting the PCM take some of it away?
So, to squeeze more power outta the 6.5, we can adjust the Base timing to ~+8.5deg, to get more complete combustion by getting the fuel into the cylinder earlier in the combustion event.
Works well at low rpm, where the injection event window is wide, but would hinder combustion at high rpm, where window is narrow, and fuel rate is high.
But, when Base timing is adjusted, so must be TDC Offset - to a more negative value, which the PCM is gonna Learn, with or without your help. Over a period of 50 starts, PCM can re-learn the TDC Offset value, if it is not within design specs.
According to the manual(s).
What gives, here?
Ah - glad you asked, folks, cause I done went and figgered it out. (Sorry GM - that's just the way I am)
TDC Offset is PCM's method of advancing the camring, such that injection pressure is reached at a correct point in the window dictated by Base timing.
Ta daaaaa ! ! ! ! ! ! Yep - I'm Bad! I'm Bad! I am just too Bad for my hat!
(sorry, folks - just couldn't resist a little self-'aggrandizement', there) :D ;)
For higher thermal output - more power - Base timing must be advanced so injection occurs within a window which narrows as engine rpm increases.
The pump's rate of pressure increase must also be advanced so injection pressure can be reached sooner within the new, narrower, window dictated by advanced timing.
Each TDC Offset value is set for the range of advance required by Base Timing.
As the window becomes more narrow with advanced Base timing, the more negative the Offset required.
Basically, the PCM has to fool itself, by assigning a negative value to Optic Sensor timing.
In correcting for this negative value, the Optic Sensor, and the camring, is advanced further than would be normal by mechanically advancing the Injection Pump.
As PCM is starting it's injection cycle based on Base timing advanced to +8.5deg, the camring, advanced to +10deg via -1.5deg TDC Offset, is positioned where the pump rollers are higher on the ramps, pressure is higher, rate of increase is quicker, injection occurs earlier in window.
PCM measures actual retarded offset between the IP shaft, via the Optic Sensor Encoder Disk in the Injection Pump, and the crankshaft via the Crank Position Sensor. This takes into account all the tolerances in and between the various mechanical components in the timing train.
It assigns a pre-programmed value, based on Base timing adjustment, to TDC Offset, which is stored in memory via the 'Learn' procedure.
Then, the accumulated mechanical offset timing number, which changes more negative with time and wear, is used to compensate for age and wear, relative to Base Timing and TDC Offset.
So - when someone sez TDC Offset is to allow Timing Stepper Motor to adjust for it's optimal timing range or position, they ain't wrong.
(Only thing it sez in the manual is 'to allow the PCM to correct back to TDC'.)
Now, you know what that "optimal range or position" involves.
Or, maybe I was the only one who didn't know.............................Nah! I'm back, and I am Bad ! ! ;)
Thanks to TDG, over in another country, eh, for suggesting a mechanical procedure which allowed me to trip over this...I mean, to this...
[ 11-22-2004, 01:27 PM: Message edited by: gmctd ]
CareyWeber
11-22-2004, 07:06
Originally posted by gmctd:
da Shadow do....
So, to squeeze more power outta the 6.5, we can adjust the Base timing to ~+8.5deg, to get more complete combustion by getting the fuel into the cylinder earlier in the combustion event.
Works well at low rpm, where the injection event window is wide, but would hinder combustion at high rpm, where window is narrow, and fuel rate is high.
But, when Base timing is adjusted, so must be TDC Offset - to a more negative value, which the PCM is gonna Learn, with or without your help. Over a period of 50 starts, PCM can re-learn the TDC Offset value, if it is not within design specs.
According to the manual(s).
What gives, here?
Ah - glad you asked, folks, cause I done went and figgered it out. (Sorry GM - that's just the way I am)
TDC Offset is PCM's method of advancing the camring, such that injection pressure is reached at a correct point in the window dictated by Base timing.
Ta daaaaa ! ! ! ! ! ! Yep - I'm Bad! I'm Bad! I am just too Bad for my hat!
(sorry, folks - just couldn't resist a little self-'aggrandizement', there) :D ;)
For higher thermal output - more power - Base timing must be advanced so injection occurs within a window which narrows as engine rpm increases.
The pump's rate of pressure increase must also be advanced so injection pressure can be reached sooner within the new, narrower, window dictated by advanced timing.
Each TDC Offset value is set for the range of advance required by Base Timing.
As the window becomes more narrow with advanced Base timing, the more negative the Offset required.
Basically, the PCM has to fool itself, by assigning a negative value to Optic Sensor timing.
In correcting for this negative value, the Optic Sensor, and the camring, is advanced further than would be normal by mechanically advancing the Injection Pump.
As PCM is starting it's injection cycle based on Base timing advanced to +8.5deg, the camring, advanced to +10deg via -1.5deg TDC Offset, is positioned where the pump rollers are higher on the ramps, pressure is higher, rate of increase is quicker, injection occurs earlier in window.
PCM measures actual retarded offset between the IP shaft, via the Optic Sensor Encoder Disk in the Injection Pump, and the crankshaft via the Crank Position Sensor. This takes into account all the tolerances in and between the various mechanical components in the timing train.
It assigns a pre-programmed value, based on Base timing adjustment, to TDC Offset, which is stored in memory via the 'Learn' procedure.
Then, the accumulated mechanical offset timing number, which changes more negative with time and wear, is used to compensate for age and wear, relative to Base Timing and TDC Offset.
So - when someone sez TDC Offset is to allow Timing Stepper Motor to adjust for it's optimal timing range or position, they ain't wrong.
(Only thing it sez in the manual is 'to allow the PCM to correct back to TDC'.)
Now, you know what that "optimal range or position" involves.
Or, maybe I was the only one who didn't know.............................Nah! I'm back, and I am Bad ! ! ;)
Thanks to TDG, over in another country, eh, for suggesting a mechanical procedure which allowed me to trip over this...I mean, to this... gmctd,
Are you saying that we need to advance our base timing to +8.5
That +8.5deg is the Base (Desired) timing that results in -1.5 to -1.94deg TDC Offset, considered optimal for performance upgrade.
CareyWeber
11-22-2004, 09:50
Originally posted by gmctd:
That +8.5deg is the Base (Desired) timing that results in -1.5 to -1.94deg TDC Offset, considered optimal for performance upgrade. I see so you are saying that advancing(moving) the pump to +8.5
It could be done, if you had access to a simple scanner which would allow you to see original Base timing, so you would know from where you are starting.
Factory is +3.5deg, so rotating the Inj Pump about 2.5mm clockwise - to the driver's-side - should get you close to +8.5deg.
Then, according to some - and all the manuals - it is a simple key on - key off procedure for OBD-II to "Learn" new TDC Offset value.
Even s'posed to work in OBD-I systems, but I have no experience in that matter.
Problem is - without a scan - knowing what actual Base timing is, on your engine.
[ 11-23-2004, 03:20 AM: Message edited by: gmctd ]
G. Gearloose
11-22-2004, 13:17
thanks gmctd,!
(anyone else need a smoke?)
One delimiter here, folks, a caveat in time, as it were -
Advanced timing and TDC Offset is not a cure-all for a tired engine, or other ills.
If your timing chain is long, injectors tired, or the Inj Pump is barely able to top atmospheric pressure, this'll probably make the ole 6.5 run even worse.
GM suggests injector and pump replacement at ~60-70k miles - I would think with timing chain, to keep injection window within valve timing spec.
At any given, if your engine has ~100k, it's time for some replacement, imho.
[ 11-23-2004, 08:17 AM: Message edited by: gmctd ]
Marty Lau
11-23-2004, 09:06
Originally posted by G. Gearloose:
thanks gmctd,!
(anyone else need a smoke?) I think I need a week to read it again and again, and again, and again, then think about it and then rread it again, then one more time again just to be sure. :confused:
In an effort to get everyone on the same page in respect to TDC offset, it is just a learned value that the PCM uses in fuel timing calculations. On a brand new engine, we use a microwave timing device to set the injection pump to the 3.5 degree spec while it is running on a dyno. When installed in a vehicle and mated to a new PCM, once ECT reaches about 172 F the PCM will perform a TDC learn. It forces the pump into full retard (which is what you hear), as that is a known, repeatable position for the pump to be in. It then compares what the IP sees as TDC with what the crank sensor sees. The difference is then learned and stored as the TDC offset value. The value is used to accomodate for the various differences in manufacturing and tolerance stack up. When a IP is replaced, and the pump time set procedure is done, the PCM references the TDC offset value and performs the simple math needed to add or subtract from what it sees at the crank sensor to help time the pump. One important thing to remember - when a TDC offset learn is done, the PCM assumes that the pump is correctly timed. If you forced a TDC offset learn after say, a pump replacement, without the pump being correctly timed, you have just lost your original starting point and are at that time, somewhat stuck. That is where the "generic" TDC offset value is listed in the manuals as -.25 to -.75 comes from. That range of TDC offset is what was observed on a lot of new trucks and published as a normal value. If you loose your original pump timing as a starting point, you can plan with the advance and retard of the pump until your TDC falls into that window, and you will have the pump pretty close to correct(as compared to that set of trucks). Anyhow, I just thought I would throw that out there, as I am asked about pump timing and TDC offset frequently. Not meaning to step on any toes or anything.
Good input - no toes crunched, here.......yet! ;)
This is on the fly, so feel free to correct as required.
Internal IP timing range appears to be about 11deg, for 22deg at crank.
(Camshaft and IP drive rotates at 1/2 crank speed)
When IP is rotated advanced, or retarded, mechanical timing (offset) between Crank position Sensor and Optic Sensor Encoder Disk, bolted to IP drive shaft, does not change - it is locked to camshaft position by gearset, thence to crank postion by chainset.
(New chainsets can have up to 2deg slack.)
DSG gearsets maintain correct timing setup - no wear-related offset.
Nor is there any slack in Optic Sensor\camring.
TDC Offset, then, should always be the 'Learned" value, based on that mechanical stackup.
If stackup results in -0.5deg (avg -.2 to -.7) at +3.5deg Base timing, that unchanged mechanical stackup should also result in -0.5deg TDC Offset when IP is advanced to +8.5deg Base, as when a new, or low mileage truck is 'enhanced' for power (chainset is till tight).
(And it will run at +8.5deg and this initial -0.5deg value)
Only thing that moved was IP housing, distributor head, and Optic Sensor\camring via advance piston, locked by Timing Stepper.
According to the manuals, for an incorrect value, TDC Offset can be 'Learned' by the PCM over a period of 50 starts.
TDC Offset should then increase more negative with mileage, as timing chain and sprockets wear, where Optic Encoder TDC lags further behind Crank Position Sensor TDC.
Being long-term re'Learned' by PCM, as engine mechanicals wear.
I've read of a few hi-mileage trucks, with little power, with TDC Offset close to zero, but none that incremented more negative with wear.
I figger sombody may have been messing with them, tho.
Retarding IP results in more positive TDC Offset values, whereas retarding Optical Encoder Disk, as chainset wear increased, would result in more negative offset.
So - +8.5deg Base time can have various TDC Offset values, above and below normal -1.5deg, depending on how Tech-II is manipulated.
Once it is Learned to, say -1.87, tho, it stays there.
I'm not an expert - yet ;) - just long observation and correlation of many, many posts, and some practical experience, so dialog is good - bring it on.......
Sorry - I appear to have left this uncontended.......
My contention is, therefore, as TDC Offset is (apparently) not allowing compensation for any crank-to-IP slack, which does not change when Base timing is advanced, then it must be electronic compensation for the mechanical hydraulic pump, with it's constant-beginning injection cycle.
The camring ramp profile is being 'altered' by adjusting it's offset from Top Dead Center, closer to the on-coming rollers.
PCM hits Fuel Solenoid, starting injection, but rollers are +1.87deg further up the ramps, injection begins earlier in the window, as required by greater advance and hi rpm.
This must be done, because the injection window, already narrowed by the Base timing advance to +8.5deg, becomes even narrower as rpm increases.
Yea - or nay?
[ 12-03-2004, 06:40 PM: Message edited by: gmctd ]
Also not an expert but have always been under the impression tdc offset is to compensate for timing error from drive slack. My observation is you can move pump anywhere you want & ecm will readjust. Once ecm adjustment passes 2 degrees plus or minus it turns on s.e.s. light. I have played with the timing on my truck with a scan tool & noticed that no matter where i put pump, actual & desired timing were the same above idle. At idle you could actually change the timing. Advancing the timing & then doing tdc offset learn gives you a negative ol value as ecm tries to pull timing back to stock. -1.94 value is close to max ecm will adjust before turning on s.e.s light.
An aside - i think the stepper motor acts on the cam ring so as ecm pulls timing back to stock its doing it by moving cam ring back to factory optimal position. I would guess ecm uses crank sensor as ultimate reference as #1 is always the same - no variation.
What scanner did you use for your data, TAG?
GMCTD, you are right on the money about the 22 degrees of timing - our actual target is about 22.5 degrees (off the top of my head). You might want to keep in mind that there are actually three basic types ways of controlling the injection events, they are: pump-spill, fill-spill, and spill-pump-spill. They each have a different time to be used, depending on RPM, load, etc. During engine operation, the crank sensor is looked at in regards to engine rotation, while the OSTE is looked at for pump rotation information. Also, if any of you have noticed, no matter what your base timing is set to on the IP, once a TDC learn is performed the PCM thinks thepump is correctly timed, and the value displayed on a scan tool should be 3.5degrees, whether that is where it was at or not. Now I have to read that first AND second posts again.....
Thanks - your input fills in more gaps.
I recently upgraded my IP from 5288 to 5521, installing the new IP at exact same rotational location, as determined by imprint in aluminum timing cover.
5288 had been set for +8.5deg with -1.5deg TDC Offset.
After priming and bleeding pump\pipes, engine fired right off.
Immediately checked with Tech-II, Desired and Actual was +8.5deg, TDC Offset was -1.5deg.
Did Time set, TDC Offset Learn, timing stayed +8.5deg, TDC Offset moved to -1.82 - fairly close tolerance for pumps of '95 and '01 chronology.
Did a little more persuading with Tech-II only, TDC Offset moved to -1.94, where it is now.
Desired at +8.5deg, Actual fluctuating some between +8.5\+9.5deg, TDC Offset at -1.94deg.
Recently changed out PCM, for some experimental work, using spare from toolbox, which had been there since '99, when I built the truck.
With Bill Heath's v1.9 Max-e-Torq installed, truck fired right up, sounding like a Bad Cummins - and I do mean a BAD Cummins, not a defective one - leveled off, smoothed out, and I checked Desired\Actual to be +8.5deg and TDC Offset to be -1.5deg.
This would follow stated info in service manual, where 'new', or cleared, PCM will immediately Learn correct TDC Offset value, where previous value does not exist, or has been cleared.
'Course, the manual also states - 'adjusting timing from factory +3.5deg will not change engine performance or vehicle driveability, so timing must be set to factory specs'. Ha ! ! !
Sez you, I say! Ha ! ! ! !
I got yer factory specs, right here ! ! ! ! ;)
Sorry, folks - youthful exuberance, again.
Which probably ain't a pretty sight, at my age, but - there, it is.
"Pssssttttt! Know what I think, folks?" he whispered. TDC Offset variable was Chevy's way of 'sneaking' in a method calculated to support performance upgrades - pun intended.
MKlein, I get the impression you have some association with factory method and training, so, all kidding aside, I - and others - would be interested in your input.
I have studied this thing long and hard, and the factory blurb - no offense intended - about compensation for mechanical tolerance stackup doesn't appear to describe actual function.
Particularly considering the performance gain(s) afforded by ignoring factory admonishment to set Base timing only to stated spec.
Gains shown, from both mechanical TDC Offset AND Electronic TDC Offset manipulation, to be viable, and useable.
Any thoughts on this will be appreciated.
By-the-by, I disassembled a DS4-5288 IP, part of a continuing quest for knowledge on this subject.
[ 12-09-2004, 03:24 AM: Message edited by: gmctd ]
I have to wonder if you did the time set routine. If you did i think you would see 3.5 deg as base timing. after leaving time set mode it reverts to whatever the factory programmed in to the ecm, must be 8.5deg.
You're the third person to mention that +3.5deg Actual while in Time Set figure, one by using a Snap-On MT-2500 scanner.
I know how much physical IP movement results in how much Timing change, so, I'll admit I wasn't paying much attention to Time Set.
I'll do it again, and pay closer attention - I'm usually champing at the bit, waiting for Time Set to end, so I can get to TDC Offset Learn, once I've rotated the IP to new Base timing position.
However, if the factory microwaves the IP at +3.5deg physical position, a 2.5mm advance is +8.5deg, so that Time Set +3.5deg must be what - a PCM fuel\timing curve number for Backup Mode? An emissions number?
I did notice that, while in Time Set with 0 Desired, engine runs like it is in Backup Mode.
Class is in session, folks - keep it coming, please.
I am convinced 3.5 deg setting is good backup if all controls fail. I think it also puts stepper motor in middle of its travel so ecm can adjust for mispositioning of pump. The guys responding on this topic are very knowledgeable so i dont want to step on toes, but i do have a repair shop & have a lot of experience with factory ecm strategy.
I had assumed that, TAG - so, what brand of scanner are you using?
For the database, I use a 2004 Tech-II - my PCM is OBD-I......
And, JK - I may be slow, but I'm dumb - what facet of this were you illuminating, with the -1.94 post?
What did you have in mind?
[ 11-24-2004, 04:34 PM: Message edited by: gmctd ]
I have an otc 4000e & a tech1, otc is not bi di on obd1, tech1 is. My truck is 95 - obd1. gas engine is majority of my work & obd2 is pretty generic. Most of my diesel work is powerstroke. Also have mitchell repair database.
Ok - so, I did a Time Set, and PAID ATTENTION to the data, this time.
Base timing mechanically set and locked at +8.5deg, Desired and Actual at +8.5deg.
New DSG gearset, so no negative offset or slop between crank TDC and IP Optic Sensor Encoder Disk TDC.
At Time Set Command - Desired goes to 0, Actual fluctuates +3 ~ 3.5 to +4.5 ~ 5deg, engine runs smooth, but retarded, labored .
However, as engines factory set at +3.5deg Base\Desired run smooth and well, this- as the gynecologist said - bears some looking into.
So - any relevant info-data from the factory camp?
[ 11-25-2004, 08:02 PM: Message edited by: gmctd ]
Originally posted by gmctd:
da Shadow do....
Never thought I'd hear that version of that line again! ;)
Now I just have to figure out if the tech stuff makes sense to me or not.... My head hurts!
Originally posted by gmctd:
I had assumed that, TAG - so, what brand of scanner are you using?
For the database, I use a 2004 Tech-II - my PCM is OBD-I......
And, JK - I may be slow, but I'm dumb - what facet of this were you illuminating, with the -1.94 post?
What did you have in mind? Basically, we can debate this till the cows come home, but in every case, the only appreciable gain that I have seen was by setting the TDC learn to a larger negative number. -1.94 is largets on pre 96 models, and 96 up can run as far as -2.38, BUT it ccan get pretty raspy...
Time set just either "centerizes" the stepper motor as does TDC learn, or goes to direct crankshaft sensor firing. The correlation between 3.5
Good data - I've noted similar, including Offset went to +2.4, with DTC, once.
Based on some syntax in the manual regarding this, are you adjusting IP with engine running while in Time Set Command?
I've designed a micrometer-type tool to do this, but have not used it.
And your Tech-II does display final Desired and Actual at +8.5deg?
Desired and actual will track together, but will vary based on temp and RPM. You should see the desired start upa bit higher if you unplug the ECT sensor at startup.
Move the pump all you want, and so long as the steeper has sufficient travel, it will get you there. If you move it too far ahead, and it cannot get where it wants to be it can set a code.Even if it cannot get the timing right, once the timing comes into it's "window" the desired and actual will track together.
GMCTD,
To make sure I understand, for people like me that will replace an IP at home without a TechII.
I have a reader that can read TDC Offset and actual and desired timing. When installing a new IP you:
1. Install the new IP, adjust IP position for an actual timing of +8.5.
2. Key on, acc to floor procedure to learn TDC.
3. If TDC offset is still not -1.5 to -1.94 then advance pump towards drivers side, goto number 2.
Is this correct?
Thanks, Andy.
A sequence of events with my OBD-I truck, where IP was replaced on original PCM, and later, spare PCM was replaced on the new IP, leads me to believe this procedure is do-able, and can be done on OBD-II systems, as well.
Do a scan to get a base Timing reference - +3.5deg is original factory setting.
Disconnect both batteries, so PCM will dump.
Try to install the new IP to the exact original position - the timing cover will have an impression of the previous IP gasket in the machined surface.
You can also duplicate the clamp-nut scoring marks on the old IP flange to the new IP flange.
Some precision is required here, to get close to original Base timing.
This is to ensure the engine will start and run normally.
Remove the glow plugs, crank engine to prime and bleed the IP and injector pipes.
Reassemble everything.
Start engine, do a scan and compare new data to old, and allow engine coolant to reach 180deg.
If timing scan is close to previous, but engine runs rough, shut it down, disconnect Optic Sensor, crank and let run about 15mins, to allow IP and pipes to purge.
Engine is running in Backup Mode, allowing for such contingencies.
Stop, reconnect OS, and try again, allowing ECT to reach 180deg.
TDC Offset may learn immediately, but will learn at that point.
My test PCM learned the Time and TDC Offset immediately, as I had pre-warmed the engine to 180deg.
No Time Set or TDC Offset Learn procedure was required - Tech-II immediately displayed +8.5deg Desired\-1.5deg TDC values, after the Cummins-growl episode.
Then, for a scan of +3.5deg, move IP 2-2.5mm to driver-side, should put you in the +8.5deg ballpark.
1mm IP adj is ~2deg crank timing.
Do the TDC Offset Clear and Learn procedure when IP Base timing adjustment is correct.
Anyone who's done an IP R&R multiple times may want to post any cautionary data to the contrary.
Will disconnecting the optical sensor serve the same function as commanding the 0 degree timing fuction on a Tech II?
No - Time Set is a specific function for electronic and mechanical inter-reference.
By calling for 0deg desired, it retards the camring to mechanical stop of Timing Stepper motor, then measures the distance to TDC on the Encoder Disk, referenced to +3.5deg.
Tells PCM the actual position of the fuel distributor head from 0deg TDC
Disconnecting Optic Sensor allows engine to run on Crank Positon sensor timing.
Engine does run similar under both conditions.
GMC Hauler
11-28-2004, 21:39
To GMCTD:
So, what do you do, if you found your injection pump loose, tightened it up, and havent had the pump retimed yet? It runs fine, tows fine. I was waiting to get the performance computer in before I made one trip to the dealer to time it. I have been reading posts for about a year now to figure out if i can set all this without a Tech II, just a scanner that can read TDC offset and timing. The service manual helps some. My post is a variation of AndyL's. Seems to me, I can do all of this at home with a code reader that can read TDC offset and timing, correct?
Yes - do the scan first, for reference.
Have the PCM out of it's pocket and ready to chane out, so Engine Coolant Temperature remains above the Learn temp level during the swap.
Pre-warm the engine to idle temperature, above 180deg.
Shut down, switch PCM's, and the re-flashed PCM will Learn the parameters when the engine is running.
GMTCD, I do work for General Engine Products, which gives me access to what was originally designed in regards to pump timing set up. But to keep beating the dead horse and to throw out the old factory line, TDC offset is intended to compensate for the difference in stack up - including variations in front cover alignment and crank sensor mounting. However, I am not saying that you cant get some more power out of the engine by playing with pump timing. My point is only this, if move the pump a couple of degrees advanced, then perform a TDC learn, your displayed pump timing will still be 3.5 degrees. But a more effective way to do this would be with custom programming, something to take advantage of the different timing. As a side note, I set pump timing with the engine running, using the kent moore spanner wrench ( I recall somebody mentioning that). And I sure don't think I know it all - or even all that much on the subject, but I enjoy the discussion. Keep the stuff coming! I've got the enginnering staff going now.....
If I can remove a PCM and put it on the shelf, then return it to service and still retain the same TDC offset value, how will unhooking the batteries help?
Glad to see you back, Mklein - your input is very welcome, and highly appreciated.
Already, with two short posts, you've filled in several gaps in a quest for understanding this 'magic' box.
My background is hydraulic, pneumatic, NC, computer\electronic measurement\control and amateur automotive hobbyist, with heavy emphasis on 'how does it work?'
I understand machining tolerance specs, tolerance stackup, the mechanical compensation for this, and variances of electronic compensation for this.
My experience with the EFI 6.5 is OBD-I, with some OBD-II input, and I have a Tech-II.
I am here to learn, and I have read the factory 6.5L EFI training manuals and service manuals for OBD-I and -II. And everything else I could get my hands and eyes on.
I (we) have been looking for someone willing to teach, or explain past factory adherance to EPA and warranty considerations. (No factory EGT and Boost instrumentation or charge-air cooler.)
No offense intended.
And, I am prepared for some embarrasment..... ;)
The truth is out there.
To restate - TDC Offset is electronic compensation for mechanical tolerance stackup, according to GM Training manuals and Service manuals.
Factory Timing spec is +3.5deg with average -0.2 to -0.7deg Top Dead Center Offset, due to stackup.
Manuals also state - advancing Base Timing will not result in increased performance or driveability. Adjust only to +3.5deg factory spec.
My contention - if TDC Offset must be re-'Learned' at any instance of mechanical replacement, why does it not reflect accrued wear-related offset?
Timing chain wear should show at least -2deg at 50k miles.
Secondly, advancing Base timing to +8.5deg invariably results in -1.5deg TDC Offset with old or new timing set, and can be managed either side of that, to about 0.5deg.
Mechanical stackup does not change when Inj Pump is rotated to new position, yet total Offset should show included wear-related stackup.
Advancing Base timing does result in improved performance and driveability.
Hopefully, you can shed some light on this, and thanks for your interest.
Hey, I agree with you - the truth is out there, and if I knew what it all was, I would definitely be sharing. With that said, I don't have an answer for why you don't see the change due to timing chain wear. What you do see when you change the pump is the difference in what the pump sees as TDC as comparted to the crank sensor. That relation is what allows the pump to be timed after replacement. Assuming the original TDC value prior to pump replacement was correct (correct meaning that the pump was correctly timed to 3.5 degrees, and the TDC offset value had been correctly learned), the PCM uses the TDC offset value to calculate what the pump timing currently is, so you can advance or retard to get your 3.5 (or whatever you like). And I won't disagree with you on the difference in performance in advancing timing. I've seen it myself, what the manuals say is not correct. The only pitfall with doing this is that you have the effect over the entire operating range of the engine. That is the beauty of changing the calibration - you can get both power under throttle, and mileage under cruise. With that all said, I, of course, am running a mechanical pump on my personal vehicle. Too damn tired of chasing sparks all day long I guess.
There are a large number of people here that would agree with you on the mech IP - I was headed there 'til I got the Tech.
For now, I'm having too much fun to do the change-over.
And please consider all my responses as posed as a giant question.
I could understand that the -0.5deg avg may be a compensating reference based on new parts, which the PCM then corrects back to from any accumulated(ing) wear, but does not display the accumulated compensation.
That concept still does not offer any reason for the -1deg increase from +3.5deg to +8.5deg on a new DSG gearset.
To recap here, all in one spot -
I read a procedure, by a young fellow with excellent Stanadyne Inj Pump background, whereby the Optic Sensor is physically retarded on the camring.
PCM comes on line, sees the Optic Sensor is out of position, advances it to correct, which then advances the camring ahead of factory expectations.
PCM closes Fuel Solenoid to start injection , rollers are now higher on the ramp, injection pressure is higher sooner after the valve is seated, injection occurs earlier and longer for same Fuel Solenoid on-time.
I assume this works positively with the Spill Accumulator.
PMD resistor is reduced to lowest value possible, with idle quality, to increase fuel rate.
Problem is, this occurs from idle to full power, and because PCM does not know the camring is advanced, out of position, idle quality can be severely effected.
PCM now has some trouble with cylinder balance.
Performance increase is notable, injector tick is crisper, with some rattle increase, based on responses of those who tried it.
This immediately seemed significant to me, where that mechanical retard\advance, and it's results, closely echoed the results and the -1deg increase the PCM set when Base Timing was advanced to +8.5deg.
Set Base Timing to +8.5deg, leave TDC Offset at -0.5deg, engine sounds 'different'.
Do TDC Offset Learn, injector tick gets crisper, Diesel rattle more pronounced when Offset reads -1.5deg.
PCM knows this, and compensates at idle for cylinder balance.
Then, again, maybe it's just the 2004 Tech-II trying to make sense of the data stream from the '95 OBD-I PCM.
Or, me trying to make sense of both of them......
Who knows? But I got my suspicions.
Base at +3.5, TDC Offset at -0.5, increase rpm, PCM advances camring timing to compensate, Optic sensor\camring relationship allows injection pressure to occur within the window set by rpm and advance.
Increase Base advance, rpm advance increases accordingly, injection pressure must be reached sooner so injection occurs earlier, to fit within narrower window.
We see the effects of the Base timing in crisper injection and rattle, and because the PCM is aware of this, idle quality is not effected.
And, assuming the camring conjecture is sound, PCM uses the increased Offset at higher rpm where it is needed, but not at idle.
Now, hopefully, the folks in engineering will offer some crucial data, informative either way.
Almost fergot - you mentioned variances of pump-fill-spill routines vs rpm and load.
Would you correlate those to the actual conditions and requirements?
[ 11-29-2004, 06:18 PM: Message edited by: gmctd ]
eracers999
11-29-2004, 17:07
Keep in mind that the more fuel and boost you put to a diesel engine the more retarded the timing should be. Case in point, if any one has ever done a 290 small cam cummins hop up to lets say a 420 you will install a lower compression piston kit, i think its 14.7 to 1 on the 290 to 13.3 0n the 420 and then you will have to re time the cam followers to almost all the way retarded. You will tear it up if you dont. It will sound all snarly and real responsive but will not last long, you will be real hard on the counter bores also. I have tried the hot -1.94 and felt uncomfortable, ive tried the -1.50 and it still felt to hard on it. I weighed what gains Ronnie jo got on JK's dyno at 2 to 3 rwhp and weighed that against the exsessive engine heat and cooling problems created. I have mine down to -1.23 and like it there because the engine sounds like its right when it settles in to a hard pull. I can hear the timing come out of it when it goes to work.
Kent
Advance timing for cruise does retard for loading, as up a hill, where torque is needed.
I tried setting Offset from -1.5deg back to -0.7deg because my truck is big and slow, needing more torque.
ronniejoe's dyno run, with broadened torque band, convinced me to reset to -1.94.
But, you're talking camshaft timing where smaller engines do not have that luxury.
Except, with timing chain wear.........
And, any one who has replaced a loose hi-mileage timing set will swear by the power increase (restoration).
We're talking injection event timing into the cylinders with stable valve timing.
[ 11-29-2004, 06:24 PM: Message edited by: gmctd ]
GARY PAGE
11-29-2004, 17:58
So, pretty detailed analysis; but when the thing pulls 10K LB RV up and down all over why worry about it, it't a Chevy,not a Cummings just keep up the service and get the service manual to fix it up!!!
Can't do that, Gary - I gots to know......... ;)
eracers999
11-29-2004, 21:33
Yes i am talking cam timing and also injector timing, 2 valves 1 injector per cyl. Just for curiosity sake i wonder where the line is you stop making a hp increase being that RJ went from somthing like -.070 to -1.94 to get to the 2 to 3 hp increase. I know RJ had a helluva time keeping the temps under control in the mountains . A loose chain driven motor will run quieter and lazier than a gear driven motor. Can anyone tell me if the gear set that is available is timed from DSG straight up or do they build some advance into it over factory specs. 1 more question does anyone have the specs for witch to degree a cam in with. Thanks.
Kent
Turbine Doc
11-29-2004, 21:43
Okay JD I just printed all 26 pages of this; dialog you started too hard to digest on line, I'm going to sea next 4 days (Turbine job not Diesel) will converse some more when I get back in. We have talked on the phone at length about this, maybe some anomalies with my MT2500 vs T2.
Hope to get some time to compare the 2 tools in Houston with you in a couple of weeks. Will give you some time on later OBDII with your T2.
Andy L you can do a TDC offset using a reader that displays offset value. You must be 170F or above coolant temp or learn won't activate.
APP to floor key on for minimum 45 sec (I go 60) then release APP and key off for 30 sec, then do a restart truck will stumble and do the learn for value of IP current position. I loosen the 3 IP bolts and snug top only while making the adjustment after each shutdown and move to new position and learn initiate. Final snug all 3 when finished.
JD I got to agree with JK on the why you feel disconnect the batts will loose a TDC offset, I don't know why but every time I've swapped PCMs there is a stored TDC offset value in them from the previous learn even after achieving 170F which is when manual says PCM is supposed to auto learn offset, this includes when the offset learns have been completed only on my truck, same as with a new reflash or a junkyard donor PCM. (Might be unique to my truck or later model OBDII stores offset a little differently in some semi-permanent flash prom memory)
I had 1 PCM with an offset I set/learned from -1.2 to -1.6 by doing a learn and IP movement, swapped to another PCM did APP to floor learn only & no pump move and offset was -1.3, ran that way for months as I broke my IP "S" wrench when I got overzealous in my attempt to better the bends in it and em-brittled it in cool-down process.
The -1.6 PCM after 6 mos of being in back of the truck still was at -1.6 when I sent the -1.3 PCM to Bill Heath for my reflash core. That reflash came to me with a -1.2 offset in it, I ran for a week with that offset in it, I had to do a APP to floor learn and adjust to get the -1.6 to take in that PCM.
You and I have talked but can anyone else add comment or explain why offset would change PCM to PCM even though the IP has not been moved, & with just the learn command initiated.
Also suggest a reason the delta between the 2 PCMs; it seems to me from reading the manual moving the IP one way or the other is what changes the IP/cam/chain/stepper motor relationships and the learn is used to teach an individual PCM the position of the IP & stepper as installed on a given vehicle.
This post is informative & fun one of the best in a while, collectively; I think we will have a 100% correct answer, right now we have a lot of correct pieces of how it works but not all. inquiring minds got to know keep it coming folks.
rjschoolcraft
11-29-2004, 22:28
Kent,
Yes, I have had temp problems in the western mountains; however, most of my problems occurred before intercooler, fan clutch and timing change. When I went to Montana for the Rendezvous last summer, I had the least problems that I have ever had, temperature wise. At no point did I need to turn off the A/C or pull over to bring temperatures back in line as I have in the past. In fact, I think with the 180* t-stats my system will work well. Many will disagree with that statement, but MP wrote an article a while back that discussed the logic behind this and my own experience agrees with what he said.
Maybe backing the TDC offset off a little will help? I don't know. I just know that I like the way this thing runs now. At start up, it is a little louder than before, but not much. While driving (either solo or towing) it is no louder than before.
I expected a change in the sound when I went to the high pop injectors, but couldn't discern any difference. After the timing change, it sounds a little crisper at idle, louder with cold advance, but no real difference under load.
I think the timing improved throttle response noticeably, though.
For the record, the TDC offset was at -.7 initially.
PCM with flash memory and eerom will not necessarily lose data written to certain registers.
The registers can be overwritten by software procedure, which may be initiated by hardware manipulation, as in sequence of key-on-key-off steps, or Tech-II command.
OBD-II is of flash memory\eerom type.
OBD-I is Eprom with semi-volatile memory - all data is lost after several weeks\months without power.
OBD-I PCM has one ignition source connected directly to battery, to retain vehicle driveability information - very short-term - and engine parameter data, such as Time Set, TDC Offset, etc.
Remove power - driveability data is lost within a few minutes, parameters are lost within a few weeks.
Keep it coming, folks - this is all to clarify and expand on Service Manual data.
OBD-I PCM can Learn Time Set and TDC Offset on power-up under certain circumstances.
Does OBD-II PCM from any vehicle Learn when installed in vehicle with different Inj Pump timing?
What happens when OBD-II PCM with enhanced timing parameters is installed in vehicle with standard Inj Pump timing?
[ 11-30-2004, 03:30 AM: Message edited by: gmctd ]
FWIW-
From "General Motors' Diesel Electronic Fuel Injection" article series, Part 5, by Steve Garrett, 2000:
"Timing Adjustment- If the timing is okay, the scan tool will display an average of 3.5-4.5 degrees. If the timing is off, the pump will have to be rotated." Article then describes process of manually rotating IP to achieve 3.5-4.5, and that 0.040" rotation = 1deg.
"Tdc Offset Learn Proceedure- TDC learn is a non-volatile learned memory used by the computer to adjust for any variation between the position of the pistons and the crankshaft as indicated by the crankshaft position sensor, verses the actual position of the pistons and crankshaft. This procedure must be performed if the: -front cover has been removed. -timing chain or gears have been removed. -crankshaft or the crankshaft position sensor has been removed. -computer has been replaced.
Contrary to GM dealer warranty guidelines, it's a good idea to perform the TDC Offset Learn procedure if the pump has been removed. If you perform the TDC Offset Learn, you can skip the timing set procedure." Goes on to say "The TDC Learn value should range between 0.75 and 1.50deg."
Not sure how you determine "actual position of the pistons and crankshaft." I think you need a sensor, so the Optical Sensor seems like the logical reading against which to "offset."
FWI(probably not)W, I ASSumed TDC Offset was a multi variate catch-all splice between timing, which is spec-able for any particular build of this engine, and the miscellaneous potential factors involved in the various builds. I.e., I drive a 190hp, TD, blow-by version, many others here have 160hp & crankcase ventilation circulated to intake, & others still have NA versions ~140hp. Each takes a timing spec, but comes w/possible variations in other equip. If'n I'm the design engineer in year 1, & looking @ predicting all permutations of the drivetrain, I'm better off installing a buffer variable (a back door) into which I can accumulate timing related degrees of freedom, rather than trying to exactly fit each potential variable into its own memory & calculation space. If more polution control junk is required in year 3, e.g., & it affects timing, I have a shot @ putting its effect in this variable. Accumulated tolerance is one forseeable issue, tho it would make better sense to relearn this every 1 or 200 starts automatically, rather than set & forget; likewise, if tolerance stack was all that was intended, it would make just as much sense to forget TDC Offset & let the stepper motor function "self-heal" timing directly on differences of CPS vs. OS (as long as pump installation is within the requisite stepper "window", this calculation & adjustment would be obtainable in real time with no more sensors & reporting circuits than we have now).
So to sum, FWI(probably not)W, I'm w/GMTD & question the logic of the Offset variable as only a one-time cure for tolerance stack-up; if that's all it is, it is a crude stab at best & a failure of logic over the lifetime of an engine. But of course, if Offset is a back-door, why isn't it more successfully used in later 6.5 production years' PCMs?
If only engineers were logical.
GMTD- if you don't have the Garrett articles, I have a spare copy I could send you. Mike at Fleming dot cc. Good reading for a budding IP vivisectionist.
Excellent, as usual, input, UC - restates the case, well. IS worth what it's worth.
(Any sign of them cows, yet, JK?)
I have been searching for a logical explanation of the extra negative 1 degree "Learned", for merely rotating the IP in a positive direction.
OBD-II Service manual states - TDC Offset Learn is not required in case of Inj Pump replacement.
(Could mean - don't do it before Time Set)
(Or, and I do suspect this, the Inj Pump is of extreme precision matchup, unit assembly to unit assembly - don' need no steenkin' TDC Offset re-Learn!)
Do the Learn if any of the other timing stuff is replaced.
Rotate Inj Pump to driver's-side if engine stalls in TDC Learn.
That last would indicate some concern with increasing wear-related negative stackup.
Or, that replacing anything but the IP increases negative stackup.
Worn timing chain set retards camshaft, Inj Pump drive shaft, rollers and rotor.
Replacing worn timing chain set results in advancing cam timing, IP shaft.....
"Who knows?" quoth the maven.
I'll take you up on your article offer, and thanks - I do appreciate it.
[ 12-01-2004, 12:00 PM: Message edited by: gmctd ]
I ASSume the lack of TDC Offset Learn (TDCOL) @ IP change is the combined ASSumption by GM that a) a newly installed IP is factory certified to correct timing vs the 3 flange bolts, and b) the IP tolerances so vastly exceed the rest of the drivetrain's, that accounting for it will be superfluous (basically what gmtcd said above). Its stupid because, a) the TDCOL is an easy task, & b) OEM certification is good for the 99.9% of the time it works, but the 0.1% of the time it is goofed up, you install a bad IP & don't do TDCOL, will drive the diagnotician absolutely mad. Which, of course, I have long hypothASSized was a corporate goal @ GM anyway.
Or - could be just a big misunderstanding, as the tech-writers were not from a technical English-speaking culture. :confused:
Who.......knows.......? :(
[ 12-02-2004, 02:58 AM: Message edited by: gmctd ]
About the gearset, Kent - I'm fairly certain the ~2deg advance is makeup over new chainset slack.
Iirc Napa sells a replacement 6.2\6.5 camshaft - try their specs.
Or - do a search for EWC - iirc he posted some specs.
Or, maybe grape.
Originally posted by gmctd:
About the gearset, Kent - I'm fairly certain the ~2deg advance is makeup over new chainset slack. The crank reluctor wheel that comes with the DSG gear set has a built-in advance, 4*, IIRC...
Where did you see that info, JohnC?
I'd read that, too, somewhere, but cannot find it.
My gearset came directly from DSG - all I got was installation inst, and that installation would stop timing fluctuations caused by chainset.
Back in the '60s - yeah, replacement gearsets have been around that long, folks - it was proven that a gearset could provide up to 2deg advantage over even a new chainset.
[ 12-03-2004, 04:00 PM: Message edited by: gmctd ]
eracers999
12-02-2004, 10:59
I appreciate the info guys. I have a problem with them advancing a cam 4deg on a turbo charged engine that has 21 or somthing to 1 static compression. I can see where starting and drivability would be improved. I can see where a 18 to 1 pistoned motor would greatly benifit from the increased cyl press from advancing the cam. Would there be a way to change that 4 deg on the reluctor wheel or would you have to run a bushing in the cam pin. Thanks!!
Kent
Maybe oem retarded cam by 4deg for EFI emissions.
Who knows.......
MKLEIN - I keep wondering about the timing procedure with the microwave fixture.
Would you mind explaining that, including mounting and target, engine rpm, and ECM type?
[ 12-03-2004, 02:45 AM: Message edited by: gmctd ]
Originally posted by gmctd:
Where did you see that info, JohnC? I don't remember...
Thought I'd read that somewhere, also, JohnC, but have not found it....
Did read the Garrett piece (tnx, ucdavis)- it's right out of the manuals, but in a more personable delivery.
Musta been a DS4 EFI instructor.
He does rec TDCOL over Time Set for IP replacement, contrary to factory directive.
Me - I'm stickin' to my guns for the next nine years, when the last of the 2002 eleven-year 125kmi IP warranties expire.
Betcha then we'll have ex-GM and -Stanadyne gnomes comin' outta the woodwork, talkin' about the TDC Offset backdoor, and performance gains that coulda\woulda\shoulda been had by messin' with it and Time Set. ;)
I'll be 73, then - wonder if I'll still remember what it is they're talkin' about?
Or, care? :rolleyes:
Surley Jamie from Diesel Depot has degreed enough of these CAMS to know if they were all 4 degrees off from the factory?
Bobbie Martin
12-08-2004, 17:25
Originally posted by Kent:
I have a problem with them advancing a cam 4deg on a turbo charged engine that has 21 or somthing to 1 static compression. I can see where starting and drivability would be improved. I can see where a 18 to 1 pistoned motor would greatly benifit from the increased cyl press from advancing the cam. Would there be a way to change that 4 deg on the reluctor wheel or would you have to run a bushing in the cam pin. Thanks!!
Kent I've often wondered if the reported HP gains from the gear drive didn't come from the cam advance, not the gear drive. I agree advancing the cam on a 21:1 engine might hurt (probably work great on a 18:1) but I really haven't heard of any reported problems from this. It always surprised me GM kept the same cam timing on the NA 6.2 as the turbo 6.5. I'm sure there is some HP there, but its just not financially feasible for a cam grinder to spend the dyno time for such a small market. An offset cam key would advance the cam without changing the IP timing (essentially this is what the gear drive does). Finding one might be a trick, maybe a gas Chevy V8 uses the same key and if so shouldn't be a problem. This is the only place I have ever seen the cam specs for a 6.5 Cam Timing Page (http://www.goautocenter.com/6_2__6_5l_diesel.htm )
eracers999
12-08-2004, 18:29
[QUOT The crank reluctor wheel that comes with the DSG gear set has a built-in advance, 4*, IIRC...
--------------------
JC - Member #1346
'95 K2500 6.5TD - Kennedy Exhaust & tow chip
'93 C2500HD 6.5TD was 4 Sale, now wrecked, parting out, call!
'03 Zetor 4321
'99 K1500HD 5.3
'87 F350 7.3 , '78 D150 318 (Sold)
--------------------------------------------------------------------------------
E] [/QUOTE] John C.
I've never used the quote thing before, it looks funny to me, anyway. Wouldent 4 deg advance on the reluctor wheel (being that it is on the crank ?) just effect pump timing only ?? It might be in order to call the tech guys at DSG and see what they say.
Bobby;
I think we are on the same page. Before i spend on a gear set i want to know exactly what im changing besides just adding gears. I think all the tech data should be obtainable for those who have to know.
Kent
Originally posted by Kent:
[QUOT The crank reluctor wheel that comes with the DSG gear set has a built-in advance, 4*, IIRC...
--------------------
JC - Member #1346
'95 K2500 6.5TD - Kennedy Exhaust & tow chip
'93 C2500HD 6.5TD was 4 Sale, now wrecked, parting out, call!
'03 Zetor 4321
'99 K1500HD 5.3
'87 F350 7.3 , '78 D150 318 (Sold)
--------------------------------------------------------------------------------
E] [/QU0TE] John C.
I've never used the quote thing before,Looks like a cut-n-paste error to me. the quoted stuff has to fall between and . You'll note that the first part is broken up and the quoted stuff falls between the "T" end "E" of the initial [QU0TE]
eracers999
12-09-2004, 21:22
Ill get it right one day.
Kent
Have done OBD-I Time Set, then TDC Offset Learn several times in past three months for verification - each time, Desired and Measured indicate +8.5deg, TDC Offset indicates -1.94deg, which would indicate PCM is satisfied with that pump position.
I wanted to reduce TDC Offset to -1.50, as -1.94 causes the indirect-injection combustion chambers to rattle in mortal agony on these cool 40-50deg mornings.
Thought I'd try JK's tip of varying idle rpm to get different numbers.
I was able to select from numbers between -1.04 at ~1500rpm to -2.04 at idle - made it easy to set up my desired -1.50deg.
Seems to blow a hole in the accepted theory of compensation for mechanical timing train slack, particularly since mine is the DSG gearset.
It would appear that the PCM is adjusting some dimensional positioning numbers, based on increasing rpm.
RPM increase does NOT increase or decrease measured mechanical offset due to slack........
Anyway - tnx, JK - 'nother piece in the puzzle.
[ 12-13-2004, 03:30 AM: Message edited by: gmctd ]
captaincrunch
03-15-2005, 17:12
I just read this whole thing, and man . . . am I dumb! You guys must be rocket surgeons or something!
So . . . what exactly should I be looking for in my truck?
1996 Light duty (L56), IP replaced 60k miles ago, just put in new injectors/HO water pump/Phazer Gears/glow plugs (thanks JK). . . /power steering pump/vacuum pump.
Mechanic aligned the marks on the IP back to where they were. I notice a lot more noise now at idle (like a Ford). Sounds good while driving (except for a whine . . . I guess it's the gears?).
I've opened up the air way with K&N filter, replaced the intake manifold with a L65 and cut out all the junk in the old plenum and removed the EGR. 3.5" mandrel bent exhaust with 4" Magnaflow muffler (stock down and crossover).
I'm looking for economy. I don't pull much anymore.
I don't have access to a Tech II (Dealer wants $180 to set timing).
What's the best suggested TDC offset. Should I pay the dealer or try it another way?
Any suggestions?
-1.94; -1.50; . . . what?
Any adjustment requires a reference scan, to know actual current Inj Pump position - should be +3.5deg and -0.5deg TDCO.
+8.5deg and -1.5deg TDCO works well with the reflashed hi-output programs.
Some run the -1.94deg TDCO, but the first 40deg morn generates audio experience reminiscent of a half-empty cement mixer, short on water, heavy on the rocks.
Whereupon,I timidly opted for the saner setting, at -1.5deg.
Yeh - I'm a wuss....... ;)
patrick m.
03-15-2005, 18:36
so would this explain why i could tell no difference in -1.94, -1.00 off set after installing my mew "chain set".
I did mine back when there was much discussion about cranks breaking and all had gear drives.
(All also had bad balancers)
or maybe my pump is getting weak ;)
rj's dyno run indicated only +3hp gain, but raised and flattened the torque curve just below 2000 to above 2500rpm, right where we need it for hd work, by increasing TDCO from -0.7deg to -1.94deg.
Still unclear as to whether that was done by manipulating rpm and TechII, or by rotating the Inj pump +5deg, for +8.5deg Des\Act timing at idle.
Turbine Doc
12-30-2005, 22:34
Hey bumping this back up to top some very good info in here.
Slim shady
12-31-2005, 09:42
I just read the whole post and man my head hurts. A lot makes sense and some of it will take time to push in there. I know why I joined this group now.
Thanks
PS. always was told in GM school it was voodo to mess with factory settings,never did listen :D
patrick m.
12-31-2005, 10:16
i really hope JD drops in sometimes.
Turbine Doc
01-02-2006, 00:00
Next time you get to missing him give me a shout, I have his frequency and can holler him in, he says that even though he has gone to the "other side" he's still willing to lend a hand along with his brand of humor.
GMCTD, I forgot all about this thread - and never answered your question about microwave timing. The device generates a microwave signal, which is reflected in the chamber, and based on the rate at which the signal is relected, the exact location of the piston in the chamber can be calculated. Basically, a microwave sender / pickup is threaded into the number one (or whichever cylinder you desire) glow plug hole. Taps are made off of the OSTI to pick up the high res and cam signals. All three of these cables are then connected to the timer. Once the vehicle is warmed up, the pump is put into full retard by either a Tech 2 or some of the PC programs that we use for development. Anyhow, from that point we can measure the injection command as it relates to TDC. The timer is fairly generic in its construction, its the software that is written to go with it that sets it up for a particular application. By the way, all of the complete electronic engines that are built by GEP are microwave timed during the hot test. We do see the timing value fluctuate during pump timing, as the timer is far more accurate than the mechanical systems that they are measuring.
Thanks, I appreciate the update -
Would appear to be much more accurate than the optical combustion sensor, with the piezo element in cyl#1 injector pipe on the old DB-series inj pumps.
Marty Lau
01-04-2006, 15:20
Originally posted by 16ga SxS:
</font><blockquote>quote:</font><hr />Originally posted by G. Gearloose:
thanks gmctd,!
(anyone else need a smoke?) I think I need a week to read it again and again, and again, and again, then think about it and then rread it again, then one more time again just to be sure. :confused: </font>[/QUOTE]Okay, I have read this a couple more times and I think I understand...............about 15% now. Where is that Makers Mark bottle! ;)
I better read it about 4 more times.
OK, I to have read this thread many times.
Still Quite confused,
Please: Can you answer 2 questions ( In dumb speak)
1. Is a TDCO of -1.8 more advanced than -.5
IE Combustion is sooner with relation to
crank rotation....
2. Truck was timed at approx -.5, 50k miles
later I Did a TDC learn and it went to -2.5
WHY, if wear should make TDC later in crank
rotation....
( rotated pump Clockwise as looking from
drivers seat, , now set at -1.8 )
Sure - give me a bit to collect my thoughts on the subject - I've been Cummins and goin' a lot, recently.
Briefly - it is advance
TDCO offsets the PCM's timing counter, giving the effect of physically advancing the Camring TDC position in relationship to the Optic Sensor.
This has the effect, in a constant beginning-variable ending injection system, of altering injection characteristics for a crisper injection pulse spray pattern - better burn, but more potential nox emissions.
What you observed, RJWest - -0.5 initial TDCO, apparently incrementing more negative with increased mileage due to timing chain wear - would have been correct, IF (really big IF, here) TDCO function was as described in all the official GM training and service literature.
However, as you had to rotate - retard - the Inj Pump towards the passenger side of the vehicle to reduce the -2.5deg TDCO value, your IP would seem to have picked up some physical advance, or was too advanced when the -0.5 TDCO was first 'learned'.
(NOTE: the Snap-On MT2500 reads approx 5deg TDCO at +8.5deg timing, which would seem to be the amount of actual timing increment in degrees.
Snap-On admits the value is not actually representative of TDCO.)
What actually happens is, for each physical IP advance position, several TDCO numbers can be obtained, Positive + or Negative -, but only one value is usually accepted as correct.
As in -0.5deg for initial +3.5deg factory IP position.
Rotating the IP towards the driver-side by 2.5mm from that factory +3.5deg position will advance initial timing by 5deg to +8.5deg, where TDCO will learn to -1.5deg, or can be set to any of several values with a Tech-II or other scanner, most desired being -1.94deg.
(NOTE: TIMESET function is OBD-I specific, and is intentionally obscured in OBD-II.
TIMESET function is retained in TECH-II instrument to facilitate Inj Pump replacement\adjustment in OBD-I vehicles.
Which is why you will see the TIMESET value fluctuating across +3.5deg in OBD-II PCM after Inj Pump has been physically rotated to +8.5deg position.
Factory Tech training suggests ignore TIMESET function in OBD-II, instead using only TDCO function to set up or adjust Inj Pump timing)
Check ronniejoe's dyno runs to see the net improvement in performance obtained with a chip when timing was advanced from -0.7 TDCO to -1.94 TDCO.
My interest was particularly in the torque curve across 2000 - 2700rpm.
Thanks, OK, Most lickly the pump was mechanicaly
advanced and TDCO was set to the -.5 with a tec2 ?
By doing a Key/throttle ON/OFF reset the TDCO relearned to -2.5 ? ?)
By rotating the Pump ( top off pump to passeneger
side ) The re-learn to -1.8 was correct.?
To achieve less than -1.0 I need to rotate pump
more to the passenger side ?
My oil sample went bad, I do most of my driving
at 1800-2000 rpm, I am concerned that the
advance is not good for engine longivity,'Also
some coolant in oil ( head gasket ).
Thanks for your patient and through explainations,,,,
Question: can a tech2 force a TDC learn differently than the PCM TDC learn ?
Yes.
Yes.
Yes.
And, yes.
Tech-II can set any number displayed - key on-key off routine (in OBD-II) will 'learn' only the positional number
rjschoolcraft
01-10-2006, 07:06
Originally posted by gmctd:
OBD-I is Eprom with semi-volatile memory - all data is lost after several weeks\months without power.
OBD-I PCM has one ignition source connected directly to battery, to retain vehicle driveability information - very short-term - and engine parameter data, such as Time Set, TDC Offset, etc.
Remove power - driveability data is lost within a few minutes, parameters are lost within a few weeks. The driveability part of this statement I agree with. However, during my engine project, my Suburban sat for six months with the batteries disconnected (OBDI). When I installed the new engine and go everything back up and running, the TDC Offset value of -1.94 was still there in the PCM. I drove it a couple of days this way without timing. Then when I did a TDC Offset Learn, the value pegged at -2.02. I had to move the pump a couple of milimeters to the passenger side to get the values back to where I wanted them...-1.94 TDC offset and about +8.5 degrees.
Barry Nave
01-11-2006, 12:45
...-1.94 TDC offset and about +8.5 degrees.
RJ
I tried awhile back to get this setting but the +8.5 would set a code. I got the -1.95 at +3.5
The committee is still out on that one, rj - I have one OBD-I PCM that held memory, one that lost it, and one from an automatic truck that went berserk shortly after I inserted a chip for a manual trans truck, did TIME SET and TDCO, was running fine, then blew all the 4L80E codes, went into LIMP mode.
Stayed in that state over several weeks of testing, but was all healed during testing a year later.
So, factory blurb withstanding, best bet is to scan PCM with a Tech-X when re-commissioned
Oh - and don't cross-pollinate it.
If the installed Cal-pak is for an automatic, sooner or later PCM is gonna want to see an automatic hanging off the back of the engine, no matter which eprom chip is installed.
Still scratching my head:
What I think I understand.
Pump is installed, than the timing is read by
a TECh 2 , it measures the difference between
Crank position sensor and the cam ring sensor in
the IP pump, ( this ref. number is not stored in the PCM ) pump is adjusted mechanicaly to get a
time ref number of + 3.5. ? YES/NO
The PCM know assumes the mechanical timing is
correct and counts the steps of the advanc(TDCO
LEARN ) from 0 to 3.5 and applies the variable to TDCO, this number is know used by the PCM
to calculate the advance numbers.
YES/NO
If above all wrong, I will delete all of above,
don't need no miss info in this thread..
Still can not get less than -1.8 tdco,
when I retard the timing, truck stalls on TDCO set.
I HATE COMPUTERS
To start with (pun intended) -1.8deg TDCO is not a bad number to live with.
But, try this and let's verify what you actually have.
Connect the TS-II, set it to display engine parameters, then start and bring the engine up to operating temperature, 180-190deg F.
Make note - write it down - of Idle RPM, Engine Coolant Temp ECT, Injection timing, and TDCO.
Note Injection Timing as the engine comes up to op temp - should start at +10-12deg at cold, dropping toward +8.5deg around 180deg F, based on your posted -1.8deg TDCO.
This will prove the Timing Stepper Motor is functioning.
Leaving Tech-II connected and powered up, kill the engine.
Do the OBD-II fingersy-footsy waltz on the accel pedal and ignition switch to clear TDCO timing - we're gonna let the PCM "learn" TDCO naturally, using the TECH-II only to monitor the result of the procedure.
Start the engine, which should still be at operating temperature, whereupon the engine will stumble a bit as PCM finds TDCO and stores it.
Again. note Idle RPM, ECT, Inj Timing, and TDCO after the "learn", when the engine smooths out.
This will give you a base to work from, and if you will post the before and after numbers here, we can proceed to the next step.
OK: Fist, I do not have a tech 2, using a 'Carcode scanner on my laptop ' it does the
time set and tdco cmd's, I believe there are correct , but not 100% sure, My attempt at comparing to a tech 1 were a failure as I believe the Mech was not
well versed in the 6.5 L.( did not want me around when working on truck )
My readings were , at 180 degrees ( thermostat)
as you described, The TDCO Learn sets at -1.8 most of the time, ( some variation ) the idle is +8.5
after warm up...and goes up with rpm, IPT and IPTD
tracking.
The mech time is about 3.5, ( fluctuates )
will redo the numbers If I get brave, getting concerned that I may really screw things up.
Question: If pump is mech. advanced +4.0
will the TDCO Learn compensate and set a
more negative number ( -1.8)?
Sorry to be so scewed up, If I could find a
good mech I would have them do it, but my experience has been that the more they do the worse it gets.. Think i'll just leave it were it is for a while...as you suggested.
Your +8.5deg timing and -1.8deg TDCO numbers are correct.
You would rotate - retard - the IP ~2.5mm to the passenger-side to get back to factory -0.5deg TDCO.
Be best to decrement the rotation a little at a time, doing the "learn", then read the result.
As timing is retarded, TDCO decreases to a smaller number - less negative, as in -1.8 to -0.5
Again, TIMESET is not a function of OBD-II, so do not use it.
TDCO is the function of choice used to adjust OBD-II vehicles.
(Yeah, I edited it - but I ain't makin' any excuses - deal with it!) tongue.gif
[ 01-13-2006, 06:36 PM: Message edited by: gmctd ]
OK, , Here are my numbers
after driving 30 miles.
Idle TDCD - 8.6 TDCA 8.6-8.7
Idle at Stop Sign , in gear, brake on
TDCD- 8.5 TDCA 8.5-8.2
Driving at 55 mph TDCD 11.0 TDCA 10.8-11.00
96 service manual states to check timing after pump install/or recheck timing"
"Use scan tool to activate time set."
" should be 3.5 if not adjust to 3.5 "
" number will flucutate , use average.
TDC Offset: Manual says to perform TDC offset
only IF: Engine replace,
Front eng cover replace
The PCM and the Inj pump have been
replaced ( ????? )
Summary of procedure: Clear TDC offset with the key on/throttle/ key off procedure.
Verify tdco is 0 with scan tool.
Start eng, PCM will relearn TDCO..should be
between -.25 to -.75
?? If my actual Timing below ( 3.5 value )
manual says to adj timing ( turn to driver side )
?? Will this make the TDCO learn go
to a less neg number, IE TDCO towards
the spec. -.25-.75 ????
The CARCODE scanner program seems to work,
but still not 100% positive on the TDC leard...
Thanks all for your patience, especially GMCTD
Desired Injection Timing is advance that the PCM has determed to be best for current operating conditions.
Actual Injection Timing is the advance measured by comparing the Optic Sensor position in the injection pump to Top Dead Center at the Crank Position Sensor.
The two numbers should be within a degree of each other.
Your Des-Act Injection Timing numbers appear to be correct, given your -1.8deg TDCO number.
If you rotate the Inj Pump towards driver-side, which advances injection timing, TDCO will increase to a more negative number, as from -0.5deg TDCO @ +3.5deg to -1.8deg TDCO @ +8.5deg
OK, with you to the last line,
I did not think the +3.5 was a 'desired'
value, but the actual timing before
the advance was calculated by the PCM.
The result being TDCD...
I did try retarding the Pump, the widh of
a ' pump mark', engine would not run during
tdco learn, thats why I reset it....
Anyway, I give up for now, leave it like it is,
Considering a new truck.... " GAS "
Thanks for your help...
moondoggie
01-19-2006, 07:06
Good Day!
I was driving along yesterday, pondering the TDC offset issue. I thought that perhaps I had put it all in one pile, & actually maybe understand TDC offset. The following is my explanation of what I surmise happens in our trucks. I
Think I'm with you up to #2:
I think the 8.5 you see is the tdc offset applied to a timing curve in the PCM ( this timing curve is not setable except by Kennedy or some other PCM programer )
IE: + 3.5 mechinical timing, is stored in the
PCM, TDCO learn adjusts this number
( TDCO value ) than this result is added to
the timing curve.
??? +3.5 + -.5(tdco) + PCM timing value calculated by rpm/boost/etc Results in TDCD
( Timing desired by PCM ) ??????
TELL ME IF I'M WRONG, DON'T WANT TO BAD INFO ON THIS SUBJECT...
moondoggie
01-19-2006, 10:30
Good Day!
Please forgive the thickness of my skull, but your post went way over head
moondoggie: REF" that went over my head "" comment
Just proves I " Don't have a clue how it works "
I thought I was a mechanic, I am now in doubt...
I have not been able to find a 'simple explaination of the IP timing and how it works.
What's even more astounding, the mechanics who work on these engines that I have meet know less than I do.....
Looked at a GM 6 litter gasser, sure looked
a lot easier to work on....
I'm sure I'm overlooking something, but I don't think it's all that complicated, for the most part. The crank shaft position sensor tells the PCM where the crank is in its cycle. The optical sensor tells the PCM where the injection pump is in its cycle. The PCM uses the stepper motor to get the pump to inject at the desired point in the crank cycle. The PCM needs to know the relation between the pump's internal "TDC" and the crank's TDC to do this. This is TCD offset.
The one thing I'm not clear on, at least I think it's the only thing, is how the PCM reacts to more negative offsets beyond simply adjusting them out via the stepper motor. I'm sure it's bee covered somewhere in this thread, but I guess it went over my head, too.
moondoggie
01-19-2006, 17:12
Good Day!
I was hoping to confirm that my description of this thing was basically correct, not get anyone else's description. I'm simply not getting it from reading everyone elses posts. :( You know, "Yes, that's basically how it works, except..." or "No, you've got it all wrong, go back & re-read so-&-so's post of (date)..." or such.
Again, please forgive the density of my skull. I'm sorta like a 58 Buick, & you know what they said about them: they might be slow, but they sure are ugly. ;)
Blessings!
(profile in previous post)
[ 01-20-2006, 03:38 PM: Message edited by: moondoggie ]
You are correct, moondoggie - TDCO is a result of calculations by the PCM, and is derived from the mechanically timed position of the Inj Pump.
TDCO is used to alter injection characteristics as rpm increases.
moondoggie
01-20-2006, 08:21
Good Day!
Thanks, gmctd, you just made my day. :D I self-depreciate my ability to understand this system, but I'm sure I'm not the only one that's struggled with what's going on here. Soooo, my hope when I asked the questions was that maybe a couple other folks might also get a basic understanding.
Is my premise about what actually goes on when we adjust for -1.94 basically correct too?
What is TDCO? If you don't have time to answer, no problem - I achieved what I wanted, with your help. On edit: I didn't catch that TDCO = TDC offset. :(
Always glad to hear from you, gmctd, even though you've gone with fewer cylinders. ;) I/we could not have afforded to pay for the help you've given us over the years.
Blessings!
(profile in previous post)
[ 01-20-2006, 03:42 PM: Message edited by: moondoggie ]
Originally posted by moondoggie:
I was hoping to confirm that my description of this thing was basically correct, not get anyone else's description. I'm simply not getting it from reading everyone elses posts. Well, I wasn't sure I got it from your post, so I posted my description and left it up to you to decide if we were saying the same thing. I think we (all) agree on point (1). It's point 2 that is the area of concern. Grandpa says "TDCO is used to alter injection characteristics as rpm increases." How about a little more detail? Does he mean the PCM somehow manipulates TDC offset to get the desired injection timing or does it use the TDC offset value to determine how much stepper action is necessary to achieve the desired timing? Got me... My question is "how does storing a different TDC offset value cause the PCM to end up with a different injection timing?" Or, why didn't the programmers simply manipulate the stepper motor to achieve some factory determined optimal timing for a given set of conditions. (Or, another way, why would the engineers make a provision for any timing other than factory spec?)
TDCO is used to alter injection characteristics required as rpm increases, and is a result based on initial, or Base timing, i.e. +3.5deg = -0.5deg TDCO.
The Timing Stepper Motor merely rotates the Camring over a max 22deg range to retard or advance the injection event.
Manually increase Base Timing - advance the Inj Pump - and TDCO must also increase to result in characteristics which meet the new criteria.
TDCO alters the period - or width in time - of the injection event.
Here
Originally posted by gmctd:
TDCO is used to alter injection characteristics required as rpm increases with increased advance.Still don't know what you mean by this.
Increasing the (effective) pump rate of climb to injection pressure improves the spray pattern, and decreases the injection period ( start, pressure build, inject, end) required by the narrower hi-rpm injection window.
The improved spray pattern is beneficial across the entire .rpm range
So - what say you, venerable scoffmeister?
;) I say, "so you mean that setting the pump at a point where the TDC offset is more negative alters the relationship between the cam ring position and the PCM's desired injection timing, which alters the spray pattern?" This I can understand. Why didn't you just say so? ;)
((I recall something about this was mentioned back in one of the first 100 or so posts, but I didn't fully (nor do I necessarily still) comprehend it))
[ 01-20-2006, 01:28 PM: Message edited by: JohnC ]
You got it, John C.....
{I edited the line(s) in question for possible clarity enhancement}
Similar results can be had by moving the Optic Sensor physical position on the Camring, but, as the PCM does not know this has been done, idle and very low rpm response can be erratic, overly sensitive.
Middle-to-upper rpm improvement is comparable, less the +5deg initial advance, to -1.94deg TDCO, however.
Interestingly, several OBD-I vehicles with the Optic Sensor adjustment, but less the +5deg Base advance, 're-learned' to -1.5deg TDCO over a period of time.
OBD-I PCM can do that 're-learn' thing of it's own volition.
Thanks, I do appreciate the kudos, moondoggie - I seldom know how to respond, so as not to generate any 'chick-flick' moments amongst us manly-type men. :rolleyes:
If y'all still have questions, ask away, long as it's not the one about "Where do babies come from"......... :confused:
And remember to check previous post(s) for recent editing, as I tend to do that if they don't appear to convey intended info (and that do happen a lot, particularly since this subject has been outta sight outta mind for maybe a year, now....)
Warren96
01-22-2006, 19:35
So let me see if I have this right, an OBD1 can relearn TDCO if I mechanicaly advance the pump,without a Tech 2?
Originally posted by Warren96:
So let me see if I have this right, an OBD1 can relearn TDCO if I mechanicaly advance the pump,without a Tech 2? If it does and you have moved the pump too far, you will set a code.
There is some potential validity to the theory as I have heard from more than one OBD2 vehicle owner getting a pump calibration error DTC just out of the blue quite some time after their dealer did a PMD only (no resistor) change. TDC Learn also apparently activates Calibration Learn...
As I stated in an earlier post, an initial scan is required to indicate the current TimeSet, so you will know which timing degree you are adjusting from.
You should not assume timing is at +3.5deg, whether OBD-I or OBD-II.
If adjusting the Inj Pump does not set a DTC for excessive timimg change, OBD-I will eventually re-learn, usually within a period of 50 starts, and OBD-II can do a forced re-learn when coolant is at operating temperature.
Originally posted by Warren96:
So let me see if I have this right, an OBD1 can relearn TDCO if I mechanicaly advance the pump,without a Tech 2? This has not been my experience.
So, here's a stupid question. If it works better, why didn't they design it that way?
Warren96
01-23-2006, 13:27
I cant force a relearn on an OBD1,without a scan tool? Somehow?
OBD-I is primitive - story is, GM coerced Stanadyne to release the DS-4 before PCM and pump was ready
I think the term 'better' is more suited to
OBD-II, but a scanner is required, in either case, to determine a reference prior to adjustment.
I am sure the 'spec' was designed to prevent tampering.
[ 01-23-2006, 02:59 PM: Message edited by: gmctd ]
How about just do a TDC learn to your favorite setting and drive it/leave it 'cause all that you are affecting is the computer's notion of where TDC is located causing it to add or subtract a degree or two from it's actual timing...
Simple terms as I understand it:
If TDC Offset is -1.0
That's the general idea, I think, JK - it is just not 'safe' to do that without an initial scan.
Which scan is what some folks are wanting to avoid.
moondoggie
01-24-2006, 09:59
Good Day!
From what I've read here, & I thought I had achieved clarification of this in the replies to my 19 Jan 06 9:06 AM post, a change of TDCO from ~ -0.5 to -1.94 is caused by changing the position of the IP from ~ 3.5 degrees BTDC to ~ 8.5 degrees BTDC.
I think I'm gonna give up trying to understand this thing if this isn't so.
Blessings!
(profile in previous post)
Was correct and still correct, md (Brian, isn't it?) - location, location, location.
Or, is it "position"?
TDCO is a calculated number resulting from Inj Pump position.
Advance the IP more positive, TDCO increases more negatively.
As per your examples.
[ 01-24-2006, 06:16 PM: Message edited by: gmctd ]
Warren96
04-05-2006, 07:58
The insructions packed with a gear drive I purchased recently from Kennedy and printed by ''DSG Canada'' give a different way to set the timing than many members who have responded to this thread are using.On page 2 under ''Special timing instructions'' a] For 1994 +1995 trucks: Set tdc to -1.94. Set timeset to 3.5 to 5.0 degrees b] For 1996 and newer trucks: Set TDC offset to -1.70 to -1.90 Set time balance to 3.5 to 5.0 degrees. I hope this supplies just one more piece to this puzzle, to a topic a lot of smarter people than I are thinking about!
That +8.5deg is the Base (Desired) timing that results in -1.5 to -1.94deg TDC Offset, considered optimal for performance upgrade.
if I take my truck to have the tdc offset learned....I believe now it was set to -.70, the diesel shop who set it said the book says -35to -70. so he wouldn't set it any more...do I tell them I want it set to -1.50 or -1.94...
I want to be sure what to tell them..thanks.
Just a quicky
I am in the process of rebuilding my 6.5. I scribed the IP so it can go back on where it was.
Now if I am correct in my reading of all this techno jargon here, even after I give my Old girl a new timing chain and sprockets all will be well as the PCM will corelate things and all will be fine.
Now my engine was running fine it just blew a head gasket. Plenty of power and good clean no smoke starts so there is no gremlins in this mix.
I do intend on having a local pump shop run up the DS4 to make sure it is within specs rather than find out later when I am already tired of wrenching on this beast.
Thanks guys
Robyn
Patrick m.
06-11-2006, 17:13
since several engines are in progress.....BUMP
moondoggie
07-13-2006, 10:54
bump to top
kenisret
07-14-2006, 19:32
Back in mar.I had the int man off and the heads off to inst. new cam and timing set and to polish all the ports.When I rem the pump I left it bolted to the water pump front plate so not to disturb the timing.After reassmbly it fired rigth off no problem.I have a Genisys scan tool which doesn't read the TDC offset like the Tech II.With my scan tool at idle it says desired timing 10 deg. and it was 10 deg actual.
I have just read the entire post and am completely at a loss. I thought I had it at one point but then it got technical again and I lost it. From what I have read here, I can't see that there would be any diesel mechanic downunder that has had sufficient experience with these engines to know any of this because we have so few of this engine.
Therefore if I am going to get anywhere I have to learn. I have absolutely no idea what state of Initial timing my IP is in.(not being the first owner) I feel that I need to be able to find out where the Base 3.5 timing is before attempting anything. If I ask a question I expect to get more than one answer or opinion. But here goes...
1998 6.5TD - Is there a foolproof way to get back to factory base 3.5? For example say IP pump has been touched or replaced without scribing marks on the cover or taking an initial scan, then put back in aproximately the right position (but - how do you tell?) It may be retarded or advanced - possibly by a couple of degrees or more. Lets say the car starts first time and you do a TDCOL without and initial scan. This seems to me to be the worst case scenario without a base scan - so... How do we now get the timing back to as base point that we can work from now that we have erased the only measuring point from the PCM? OR is there some other measuring point? I guess that is what I am asking. It may have already been answered but I don't have a degree in rocket science to understand it if I see it.
I have figures at the moment of TDCD 8.5, TDCA 8.5-8.7, TDCO -1.1. I believe these figures were obtained at operating temp in D(drive) at 601 RPM.
Futher info:- I noticed when I first got the vehicle that cruising on the highway it would be noisy/rattlely/diesel knock under no load eg down hill but would quiet right down under load up hill. This has improved over 10,000 miles, I believe, because I have been using an additive to help clean the fuel system and lubricate the pump as result of low sulphur fuels. Engine still very rattlely/diesel knock when cold.
Hope I can get some answers to make some sense of this.
Cheers
Noel
ronniejoe
08-01-2006, 18:15
The computer controls timing based on what the TDC offset value is. If the pump is too far one way or the other, the computer will not be able to get the timing numbers it wants because the stepper motor will bottom. If you want factory, base timing, set the TDC Offset between 0 and -.5 with a scan tool. This will yield the factory 3.5 degrees BTDC (or really close). When you do the learn, the computer will cycle several different offset values through in sequence. When you see the one you want, stop the process and the computer will "learn" the value. If you don't see the one you want, move the pump and try again.
To get a more negative number, rotate the pump toward the drivers' side. To get a less negative number, rotate the pump toward the passenger side. It's really not as complicated as it sounds.
So...
Is this correct?
The physical TDC position of the IP case really makes no difference because the stepper motor will compensate for what ever physical TDC position the IP case is in.
If not how do I get the IP case into the correct position in relation to the Crankshaft with no "known correct" data?
I may not be quite there yet... but if the above is not true I fail to see how dialing in a number with the scanner will move the IP if it is in the incorrect position. Also it would make no sense physically advancing the IP 5 degrees to 8.5... yet this has "proven" beneficial.
Have patience with me I'm sure to get it soon.
Regards,
Noel
moondoggie
08-02-2006, 09:32
Good Day!
Please see my 24 Jan 06 post, & gmctd's follow-up. He's expert on such things.
Blessings!
(signature in previous post)
Noel:
You're really close as your TDC offset is coming in at -1.1 You can fine tune it by turning the pump just a hair toward the driver's side if you want. My feeling is anywhere between -1.5 and -1.94 is great. Everything else will take care of itself.
Burried somewhere in the discussion is ths fact that this setting puts the pump on a more agressive part of the cam ring for the injection event, which results in a quicker pressure rise and shorter injection event.
Re: your knocking, I'd guess that one or more of your injectors is dribbling a little. The fuel system cleaner is helping over time but you may want to consider replacing the injectors.
Note that the more negative timing will result in more Diesel "rattle" when the engine is cold. This is OK.
John, is that the drivers side of a LHD or RHD vehicle?! From what I have read I assume in an anticlockwise direction when viewing the IP from the cabin of vehicle.
So... Is it the position of the stepper motor that causes the injection pump to think the engine RPM is higher and therefore increases pressure to give a shorter duration injection time with the same amount of fuel? OR does the position of the stepper just allow the PCM to select a more Negative value for TDCO, and as a result of this value, the PCM tells the pump to increase the pressure for a shorter duration injection time?
RJ, I see what you mean about it cycling through different values.
I did see -0.7, -0.9, -0.1, -1.1 and -1.3. Does produce one value per TDCOL procedure and therefore you activate TDCOL until it that particular procedure gives you the value you want? OR do you have to see it cycling during the procedure and stop it when you see the reading you want? I have left it at -1.3 for now.
I'm not so sure I understand the "why" it would cycle through different values. I though that it would learn the best value based on IP position and set that one. When we select the value we want is that short circuiting that and fooling the pcm into using that figure?
ronniejoe
08-03-2006, 10:43
Basically, there is a range of values the computer can work with for a particular pump setting. You select the one you want from those that cycle through. If you don't see what you want, move the pump a little a try again. The values will change. When I refer to driver's side, I'm refering to left hand drive...didn't think about you being from Austrailia!
John, is that the drivers side of a LHD or RHD vehicle?! From what I have read I assume in an anticlockwise direction when viewing the IP from the cabin of vehicle.
Correct..Driver's side here in the states...
So... Is it the position of the stepper motor that causes the injection pump to think the engine RPM is higher and therefore increases pressure to give a shorter duration injection time with the same amount of fuel? OR does the position of the stepper just allow the PCM to select a more Negative value for TDCO, and as a result of this value, the PCM tells the pump to increase the pressure for a shorter duration injection time?
Ya may have lost me. The pump has an optical sensor that knows with some precision where in it's rotational cycle the pump is at a given instant. It has a cam that is mechanically connected to the timing gear that drives the plungers that create the pressure that pops the injector. Moving the pump negative puts the plunger on a steeper part of the cam when injecton is happening, moving the plungers faster and building the pressure faster and delivering the prescribed amount of fuel in a shorter timeframe.
The stepper motor adjusts the injection timing for various conditions including RPM.
The PCM doesn't control pressure in the pump, only timing and duration. The start of the injection cyle is fixed whereas the end is variable based on fuel rate. More fuel = longer duration. The fuel solenoid opens to cause the end of the event by bleeding the fuel out of the pumping chamber insteaad of through the injector. (How am I doin', JD?)
RJ, I see what you mean about it cycling through different values.
I did see -0.7, -0.9, -0.1, -1.1 and -1.3. Does produce one value per TDCOL procedure and therefore you activate TDCOL until it that particular procedure gives you the value you want? OR do you have to see it cycling during the procedure and stop it when you see the reading you want? I have left it at -1.3 for now.
I'm not so sure I understand the "why" it would cycle through different values. I though that it would learn the best value based on IP position and set that one. When we select the value we want is that short circuiting that and fooling the pcm into using that figure?
I think it cycles because of mechanical tolerances in the timing system, especially the timing chain. I do not know what the effect of choosing a particular value over another, but, I speculate that the most negative physical setting that results in a value that is not out of bounds would be best, or at least result in the most negative operating conditions. (In otherwords, if you have a setting that cycles from -1.94 through something like -2.37 and you lock in -1.94 this is preferable to a setting that cycles from -1.35 to -1.94 and locking in the same -1.94.) Also, I think later PCM's will accept a more negative value, maybe -2.35 or something.
it sounds like the lift pump is an important part of the system, huh. but how does core temp. play into the differing values? resistivity in current flow. ya know your wores are just laying on the manifold. could that be part of the problem?
would changing sulfer content to the leaner side as new fuel is super clean(ya right) lead to a differnt timing event. so the disign leans fuel delivery in the sense that detonation is known and adjusted accordingly? accordingly is used in the lighter meaning as best guess because the computer parameters keep it in a set. so how do you set it for an older worn motor which becomes less efficient the combustion process but still viable.
NoelB - if the scanner is indicating Des\Act timing of +8.5deg, that number is the correct Base timing for improved power.
If the timing drive is fresh - mine's DSG - TDCO will LEARN to -1.5deg at +8.5deg Base.
With the scanner in TDCO LEARN - if you increase rpm to something below 1800rpm, TDCO will become unstable as the PCM tries to correct for advance.
Note : a TDCO DTC will set above 1800rpm.
Exit TDCO LEARN when you see the number you want.
-1.94 was scary-rattley at only 50deg F, so I 're-learned' TDCO to -1.50, for peace of mind (yeah - I'm a wuss!)
My PCM is OBD-I, so I always command TIMESET B4 doing TDCO - so far, has not produced any later "surprises"
FYI - TIMESET is not an OBD-II function, so do not use it in the '96 and later trucks.
The key-on\key-off TDCO LEARN routine superceded the TIMESET before TDCO LEARN requirement
Oh, yeah - sorry about the driver's-side thing - rotate the IP to your right, as you're facing the front of the engine, for advance.
Doin' good, JohnC - just wish someone from Stanadyne would get over the 'loose lips sink ships' syndrome, and give us the straight skinny.
From the horse's mouth, as it were...............
DmaxMaverick
09-02-2006, 09:59
Doin' good JohnC - just wish someone from Stanadyne would get over the 'loose lips sink ships' syndrome, and give us the straight skinny.
From the horse's mouth, as it were...............
You'd think that now the system is absolutely "obsolete", they'd give it up. Maybe they're counting on continued sales of their faulty design. What has Stanadyne done lately, other than peddle their outdated replacement parts?
Were some problems early on with crimped connections, vaceros, resolved by soldering the crimped connections - all later Inj Pump harnesses have been compliant with that scheme.
Removing the sulphur makes for cleaner fuel (don't worry about detonation - Diesels like detonation), but the process also reduces the lubricity - you should add some 2-stroke motor oil to your fuel to protect the DB\DS IP, where the fuel is also the lubricant.
Modern common-rail EFI Diesels scoff at lubricity content, but your IP will soon crater without 'enhancing' that content.
You haven't forgotten that it's illegal - by congressional act - to adjust or modify engine parameters\output, have you?
Or, that congress stands ready to slap heavy fines on any oem associated with the fuel system of any engine, for variance?
That's the scary side of these forums - oh, so helpful with 'enhancement' - but, who's watching.....reading.....taking names......making lists?
It's the Seargent Schultz syndrome, from TV - "I know nothing......."
I was making some notes yesterday as I was using my Laptop, Carcode Cable and software on how to Command TDCOL using it. As I was doing so I commanded TDCOL unintentionally. I was also having unusual problems with maintaining connection with the PCM, and some weird things happening as I tried to get back to the figure I wanted. The figure was jumping all over the place form -0.5 to -1.5. It seemed that after I settled on a figure it would change on me when I was messing with the idle speed command. Then it seemed like nothing seemed to want to work properly. Kinda Strange. I think the PCM might have got confuselled as TIGGR would say. It was kinda hot in the car in the sun so I gave it away. I'll Get back to it later in the week. I would like to get a phaser Gear Drive - but I don't want to fit it, and good mechanics are hard to find.
I didn't think that it would relearn unless rpm was under 1500.
IN TDCOL, the idle speed command is supposed to be your left foot, not the scanner input.
Command TDCO LEARN, observe the number(s), press the accelerator pedal till the numbers include your desired figure, exit TDCOL.
In your OBD-II case, if scanned DES\ACT timing is +8.5deg, just do the ko-ko fingersy footsie thing, then check TDCO number in scan mode, then do TDCOL for the desired number.
BTW - if resuming posting a few days\weeks after a last post, it's always a good idea to read thru, beginning with that previous post.
Each thread is a living archive, updated momentarily.
Try it - you'll like it..............:cool:
Tried the ko ko ballet dance on the accelerator with no result. Did not clear the TDCO. Perhaps I am just no good at ballet.
Interesting what happens on commanding TDCOL. The timing goes from 8.5 back to about 2.9 the diesel knock quietens down and then timing comes back up again. I found that with my vehicle that the higher the engine was held above Idle the figure got closer to say -0.7 but when it was idling I could consistently get -1.0 -1.1 or -1.2 but struggled to get any higher. I did have -1.3 before but after trying for some time I had to settle for -1.2.
GMCTD you mentioned about the timing set being an OBD I thingy. The Enhanced Tests on my Car-Code has Timing Set as an option yet Car-Code is only for OBDII vehicles. I haven't been tempted to use it because I don't have any idea what it might do on OBDII system.
The ko-ko routine doesn't "clear" TDCO except as a step before the PCM re-LEARNS TDCO - result is the new value.
Except for some error, the new value will be same as the old value unless you manually increase rpm or rotate the Inj Pump.
Remember - TDCO is a calculated value based on the relational position of the Inj Pump Top Dead Center to crankshaft TDC, in degrees.
Increasing crankshaft rpm via the APP causes TDCO to be calculated to a more negative value - the looser the timing chainset, the more the numbers vary around.
If you want to get back to +3.5deg Base timing and -0.5deg TDCO, you must retard IP timing - if you scanned timing at +8.5deg, rotate the IP about 2.5mm to your left, then do a scan to check Des\Act timing for +3.5deg
1mm = ~2-2.5deg
Then do the ko-ko routine and scan for TDCO - should be -0.5deg, -0.7 is ok, but not less than -0.5, or you'll have very little 'driveability'
The official TechII scanner also includes TIMESET command so as to be functionally compatible with all the OBD-I 6.5 systems - I would imagine the aftermarket programmers included it because it is part of the programming set in the TechII.
Imo, TIMESET is obscured in OBD-II because a sharp service tech could easily gain some unauthorized insight into DS-4\PCM operational interaction - which insight is easily seen using TIMESET command in the OBD-I system.
I've taken (unofficially) all the GM training courses, minutely scrutinized the training manuals, poured over the service manuals, vacuumed every bit of DS-4 info I've run across, and the only official insight is this, from the manuals - altering Inj Pump timing will not result in any increase in power. Period.
Does that not smack of exorbitant fines for violation of congressional mandate?
But, hey, don't get me started on that - now, where'd I put that valium.................
96 truck, OBD2, Carcode Scanner. ( Feb Version ???)
Key off/key on routine will reset tdco to '0' degrees.
(Key on, carcode scan of data)
It will remain at 0 degress untill coolant temp reaches 170deg F, ( again carcode data )
At 170Deg , TDCO learn is initiated by the PMD ( you can hear the stepper motor/) and carcode TDCO scan data changes from '0' degrees to set value.
( at least on my vehicle.)
I tried forcing a TDCO while varing RPM, could not get much change, so I let the PCM set the TDCO
FYI - initiating TDCO LEARN below 170deg ECT is an invalid condition - results are non-functional, with possible exception of r&d or experimentation
But that does verify my first statement ^ - clears the previous value before learning the new,
Iirc, TechII ignores the command below 170deg - that, and TIMESET.
Reckon I should add the delimiter - yrmv for ex-GM software.
GMCTD, the TECH II might ignore the timeset feature because it was predominantly manufactured for GM. Car-Code on the other hand wasn't and didn't need to have any restrictions. I suspect that timeset might in that case work from Car-Code. I take your point about it being there because it was a TECH II item for OBDI, but I don't believe Alex would have put it there, just to disable it. That would be kinda silly since Car-Code is only for OBDII vehicles. I'll let you know whether it works or not.
The TechII doesn't ignore TIMESET - the OBD-II PCM does.
Command TIMESET, and the displayed numbers jump around, meaninglessly, as if the PCM doesn't know what to do with the command - good indication that the service\training manuals are correct.
Don't mess with the mix.
Command TIMESET in OBD-I, and a specific number is displayed, based on the rotational position of the Inj Pump - the actual timing in degrees is displayed.
Positive indication that, contrary to the manual directive, rotating the IP does vary the timing - if the timing can be altered, the power output can be improved.
Further proof is the TDCO numbers - advancing the timing increases negative TDCO.
That is, if the service tech gets past the crazy jumble of numbers TIMESET displays in OBD-II.
And if he can figger out that a more negative TDCO number is good.
While yrmv, remember that aftermarket OBD-X scan software has not been generally available until only recently, and may be improving with experience.
BTW - I intended the statement in the previous post to mean the Tech-II ignores TDCO LEARN and TIMESET anytime ECT is below 170deg - do command enable and nothing happens, as that is an invalid condition.
GMCTD, Timeset appears to work with Car-Code.
1998 6.5 engine above 170f. Commanded time set and I got a TDCD of 0.0 degrees and the TDCA moved between 2.7 and 3.5 to give an average of about 3.1 degrees. Car-Code seems to do exactly what I expected after reading this article for the members archives:-
http://www.thedieselpage.com/members/features/ds4timing.htm
My TDCD and TDCA are 8.5 at idle with the above timeset figures. Seem to me according to the timeset figures that I could advance timing according to the timeset figures.
Is it helpful to me or others that Car-Code can command timeset and get the above info?
ronniejoe
09-05-2006, 03:52
You'd think that now the system is absolutely "obsolete", they'd give it up. Maybe they're counting on continued sales of their faulty design. What has Stanadyne done lately, other than peddle their outdated replacement parts?
Legalities in the broken relationship between GM and Stanadyne. There are still vehicles under warranty out there...
Yes, NoelB, I do think those carcode features would have some value, particularly with learning the function\response\result interaction of PCM and DS4 as a system.
What TIMESET does is retard the Optic Sensor to the limit set by the rotational position of the IP housing - PCM then compares crankshaft TDC to IP rotorshaft TDC to determine it's rotational position, including retardation due to any timing chainset slack, which is then stored in memory.
PCM then compares Op Snsr full retarded position to crankshaft TDC to determine the position of the IP housing\Distributor relative to TDC
DESIRED timing is the position the PCM commands the OS to move to, ACTUAL timing is where the OS was stopped by the IP rotational position.
ACTUAL timing degrees is then stored in memory as what I term as Base Timing.
TDCO LEARN then calculates and stores the required negative offset for that degree of advance.
Again, Optic Sensor has 11deg of rotation, eqivalent to 22deg crankshaft rotation.
With Base Timing set to +8.5deg, I never observed timing to advance beyond +19.5deg, and never observed timing to go below +8.5deg
So, since max called-for advance is only 11deg crank, which is 5.5deg IP, I really don't think TDCO is a method of positioning the Optical Sensor by -1.5deg so as to achieve optimal position for advance, eh?
More likely, it is a fudge factor to allow even idle and smooth APP input, and to allow the relatively slow injection event to occur within the tight schedule dictated at hi rpm by the advanced fuel distributor position.
'Course, I've been Dodging for most a year now, and some of the DS4 magic has become a little misty, but I'm planning on crawling back under the big GMC soon for some tighten-up, and some refresher courses with an oscilloscope, and such.
See, that Dodge is mainly boring - you just trip that little eccentric in the pump, close it up, and the big 6 will effortlessly light up all four of those big michelins, no worries, no apprehension, no scary thoughts.
Just have to keep in mind how much each of those michelin's cost to replace - that can be scary, too.
But, yeah, please post anything you learn, Noel, or even suspect, 'cause it's all still interesting.
I've read up on this from time to time, and one thing that seems to pop out is that with TDCO set more advanced, base timing should be around 8.5 degrees?
I've never seen numbers this low (my TDCO is set at -1.94), even at warm idle the timing seems to show around 13 (this is with Carcode).
Does altitude have an effect on this base timing? I'm at about 5,300 ft.
I'm asking because lately I'm getting a code P0216, and in reading about troubleshooting, it indicates wrong timing can set it. Could my base timing be set too advanced? Or is the stepper itself bad?
Thanks in advance. Joe.
All I can say is thanks for the great write up. Hats off especially to GMCTD. I had code P1214 pop up yesterday and got great support from GMCTD on another site. To make sure I understood his write up thoroughly, I subscribed to this site for further investigation (no offense, GMCTD).
All in all, a very good overview of what is happening in regards to IP timing and TDCO learn. Some real good points made.
Thanks for the flowers, qwo.
Base Timing is determined by the relationship of the fuel distributor head - attached to the IP body - to crankshaft TDC, and is only alterable by rotating the Inj Pump.
Max Base Timing for the stock 6.5 has been determined to be +8.5deg advanced.
TDCO is calculated from Base Timing and will vary depending on a.) timing chainset slack, and b.) crankshaft rpm, where PCM attempts to advance timing to suit increased rpm.
Altitude cannot alter Base Timing - it is mechanical, and the IP is locked down.
However, advance may be alterable with altitude, by ambient temperature, and possibly the initial barometric reading at Wait to Start, but 13deg is fairly advanced from +8.5deg.
Could also be your scanner - be nice to get a comparison test for features and functional results across the several software versions available.
My opinion, -1.94 is to far advanced, Ran that for a few months, at below 32 degree, way to much rattle with cold engine, It also may be the cause of the code being set,
stepper motor can not get desired timing with the -1.94 tdco.
I set mine at -1.0, Lost a little power on initial throttle
but did not notice any loss of power with my TC loaded.
Fear of the increased rattle is relative, rj - just ask me - but if the -1.94\stepper thing is a problem, seems like everyone with a cranked IP would be posting about it, eh?
May be your scanner software, dunno
joed, if you look down in between the t-stat crossover and the timing cover and the passenger-side head at night with a flashlite, you should be able to see the Timing Stepper Motor on the side of the IP - engine idling at 180deg F, the stepper rod should be slightly oscillating up and down a bit.
Have someone kick the loud pedal to watch PCM call for a bit of advance
At 180deg ECT and 80deg F ambient, PCM should not be calling for any advance at idle - Desired and Actual timing should be +8.5deg
As an experiment, if you command TIMESET, TSM should oscillate full stop several times, then fully retract, iirc - this is where PCM has commanded max retard, and Desired timing = 0
When you exit TIMESET, you will see the TSM hunt for the optimum position that allows full operational advance, about halfway between full-travel limits, favoring the retarded end.
Desired should be +8.5deg , Actual should be +8.5deg at that point.
You can also observe TSM action during TDCOL command.
Also during the ko-ko routine.
Should help to illuminate :cool: the similarities\dissimilarities between the three routines.
Remember, my input is based on TechII use, with absolutely no experience with the various software scan setups.
gmctd, in my ' screwing ' with the tdco, I had a
diesel shop set the tdco, they some how got a - 1.9 tdco set
with a tech1 ( not knowing enough at the time )
I did a tdco with the Carcode, the TDCO went to a
-2.x, don't quite rember, but it would set the out of limits
code. i'm guessing, but I think you can get the pump
messed up to where the 'cold' advance runs the stepper to the max limits...... Finially, I took a day and mechanicialy
retimed the pump, Runs good, time to leave it alone,
As for rattle, Last hunting season, it sounded like a cummins.. to much rattle for me...
While the TDCO number is important, you should ignore it unless you have noted the displayed DESIRED and ACTUAL timing numbers prior to commanding TDCOL.
Why? Good question, rj -
DESIRED timing is a variable number, even after you have rotated the Inj Pump and locked it down.
DESIRED timing is the degree of advance the PCM commands via the Timing Stepper Motor - it is referenced from the Base Timing number set by the locked-down IP.
DESIRED timing is dependent on ECT, IAT, MAP, APP, rpm, and engine loading.
ACTUAL timing is the real position of the Optical Sensor - referenced from Base timing to the Optical Encoder Disk on the IP driveshaft - as the camring is rotated by the TSM.
PCM sez I desire thus and such - IP sez what you see is what you get, actually.
Sorta like ......marriage.......ain't it?
TDCO must be calculated when ACT = DES at idle and 180deg ECT - meaning no cold advance is being commanded, such that DES\ACT = Base timing of the locked-down IP.
Iirc, one 50deg Fall afternoon, with the vehicle hood up, ECT at 190deg and IAT at ~50deg, OBDII PCM called for full 12deg DES\ACT advance at startup, slowly reducing advance to 0deg as IAT rose to above 80deg.
Also, as rpm is increased above idle, PCM will attempt to call for advance, even in TDCOL, which is why the TDCO numbers begin to jump around, and is how you can cause the PCM to LEARN almost any number you desire, within the specs for max\min DES and max\min TDCO limits
As you indicated, rj, PCM can DTC even when TDCO is -1.94deg. Causitive is a.) camring cannot move to the DES position commanded by the PCM, and b.) timing was not set at normal operating temps, such that DES\ACT is cold advanced
That is why the PCM should not respond to TIMING and TDCOL commands when ECT is below 170deg F - PCM must learn TDCO at Base Timing condition.
That is also why you should ignore TDCO prior to noting that DES and ACT timing are displaying Base Timing values.
Folks with the a\m scanner software may have to make up some hard and fast rules as you go along, and then abide by them.
OK: went back to my notes:
Here is the Story,
I had the IP replaced in Montana for a 'Stall' condition
on warm up from below 40 degrees, would happen after
about 20 minutes ( the majic 170 Degrees ).
It was a IP problem, as I was smart enough to have 2
spare PMD's , ( which all ran good after pump replaced )
SO: Diesel shop installed pump, commented the advance was
'agressive', and test drove it for 1/2 hour ( with me ).
Truck ran " Excellent" for over a year.
SO: I had a carcode, and when the new software version came out ( with TDCO set ) I thought I would try it,
Bad move, TDCO went to -2.5 ( max readable ) and set code.
OK, I did not have IP wrench so I went to Standyne shop.
They used a tech-1 tool with an adapter and got TDCO
back to a -1.90, ( without adjusting mechinical timing )
Ran this way untill trip to Maine , WAY to much rattle.
Went back to Diesel shop, asked them to Mechinicaly
reset timing to spec, They screwed with it for 3 hours,
( Did not want me anywhere near the shop when doing it )
They finially gave up, Stating that I had a computer that
was screwing up there Tech-1,
At this point I realized the tech did not know squat( not uncommon I find in florida, There all experts,Yea..)
So I went home, got some "S" "C" wrenches and made a
IP wrench for the pump.
3 Trys to get -0.9. Runs good now,
So , again, Moral of the story, If you want it done right, do it yourself...
Good story - typical Mr Goofwrench - helps swell the various Diesel forum memberships, eh?
FYI - those recently-new box\open ratcheting gear-wrenches now on the market come in several different flavors, one with a swivel-head capable of several positions to up 90deg perpendicular to either side of the plane of the wrench, for a total of 180deg.
The 15mm size in that version works wonders for adj the Inj Pump - the handle is serrated on the edge indicating the direction of force.
You just flip the handle for on or off action, flip the head to get into tight places - the ratchet action is fine-increment, allowing for close quarter work.
With a little experience, you can loosen, rotate, and lock down the IP within 5 minutes of opening the hood.
Sears has a half-off sale several times a year
Try it - you'll like it................
moondoggie
09-10-2006, 10:31
Good Day!
gmctd: Would you be kind enough to take a peek at a topic I started in the "6.2/6/5 Tech" forum? The topic is "IP Wrench" - your last post here caught my interest, & your help would certainly profit lots of folks.
TIA & Blessings!
My, my - flattery doeth ever worketh wonders....eth.....;)
I had a chance to tinker with my truck and my friends truck (also 98). I tried the flashlight on the stepper - couldn't really see anything, perhaps because it wasn't dark yet. The stepper does seem to be working though - the actual/desired timing does track down/up, and putting it in 'Timing Set' mode shows the actual timing fluctuating and you can hear the engine changing pitch.
As it relates to TDCO - my friend's truck was originally set at +0.7 - his timing still read about 13 (warm idle) on the carcode, just as my truck does. We did successfully reset his TDCO to -1.4 (after many iterations of pump moving). The only time the actual timing went below 12ish was during the TDCO set mode - it would flucuate from around 3.5 to 14. The warm idle still yields timing around 13 actual/desired. I think we ended up advancing the pump about 2mm to achieve this - any more the TDCO would go to -2.5 and set the 1214 code.
Based on this, I'm not sure I would gain much by retarding the pump on my truck?
Still trying to figure out why I get the 0216 code - it only sets when I'm towing/working the truck hard. It seems to come on after a longer uphill climb (where timing is advanced) and then going to downhill (where timing should go lower). Maybe something is sticking internally in the pump?
Thanks for all the insight, and for the tip on the wrench - that would have helped pump adjustment considerably!
Joe.
Sounds like the TSM rod might be sticking, or jammed up against a rubber fuel line, or something - that's fairly crowded down there.
Look straight down into that area between the IP and the passenger-side head to locate the TSM on the side of the IP - then try to find that angle from the front of the truck, where you can observe the rod in the bottom side of the TSM.
Also, hook up the scanner and observe IP timing and advance while driving and the code is happening - ACT should match Des within less than degree.
Still sounds like the odd readings the MT2500 displays - doesn't even compare to the TechII on a number of points.
Was preparing for some further r&d this afternoon, installing an FSD harness set up with non-loading test points, and a remote-mount extension harness - length is not too important because it is a current-driver device, not a voltage-driver.
Pre-tested several FSD modules in heat-sink mounted and bare configurations to make sure all were functional.
Guess what?
Even tho the driver transistors are fairly well damped, it is possible to get quite a tingle while holding the bare module in one's hand with engine running - insulative black plastic covers having been discarded, earlier.
That was quite a shocker - involuntarily stimulating, to say the least.
And, yeah - the bare module proceeded to warm up rather quickly, sans heatsink.
More, later.............
DennisG01
10-03-2006, 05:35
I'm shocked to hear that! ;)
glivingstone
10-16-2006, 03:30
No high tech answers here but this has been my experience with TDCO.
While checking the trailer wiring I believe my son and I managed to accidently perform the KOKO procedure which reset the TDCO, truck would hardly run when hot and blew heaps of smoke. Purchased a Carcode after recieving some good advise from this site and checked the timing settings. Found the TDCO was set at +2.5. Tried to adjust the TDCO by moving the IP to the right hoping that the TDCO learn function on the Carcode would then reset the TDCO back into the negetive, no such luck even after moving the IP 5mm, the TDCO remained set at +2.5. Also tried the KOKO but no luck either. Aftre recieving this advice from Carcode:
"Timing Set" is supported for the 98. and is OK to use the 2002 L65
vehicle selection.
TDCO Learn was not used in the 1998 engine based on scan tool information
from GM
If a item is not supported, engine will reply back with no support message,
and will not harm the PCM.
Will update the L56 and L65 for years 96+ in future.
I then tried repeatedly to reset using the timeset option, this is where it gets interesting. I found it just like playing the pokies, just keep pressing the enable button and watch what roles in. TDCO readings ranged from the original +2.5 to -1.9, I finnally settled on -1.8 after about an hour of playing aroiund and the truck runs great with plenty of power. Oh and one other thing the IPT never changed it remained on 5.4. From my experience it would seem that the TDCO has everything to do with the PCM and not so much to do with actual IP position. This also supports the theory that moving the IP position will not have any effect on power. Hope this helps to solve some of the mystery with the electronic IP.
Keep up the good work everyone.
I did not have great suscess setting the TDCO with the card code,
I do not see how key on/off could reset the TDCO as stated.
It requires the accel pedal to be depressed...
+2.5 is retarded, turning to right is wrong way
( GMCTD, check me on this )
+/- 2.5 is max readable any further movement in wrong direction will not show up...
I reset the timing mechanically, than cleared the tdco with the KO/O procedure and let the PCM set tdco when 170 degrees was reached....
Your final TDCD seems out of wack comapred with what others have seen ( around 7.5 when warm )
Just my comments,,,, not being critical..
glivingstone
10-17-2006, 03:26
rjwest your correct in saying the KOKO procedure requires the accelerator pedal to be depressed and that's exactly what happened when I asked my son to press on the brake pedal. He is only 9yo and confused the brake pedal with the accelerator, how easy it is for something to go wrong.
As for moving the IP to the right (looking from the front of the engine), this is what I believed was the right way to advance the timing.
Any comments welcome.
Seems you are correct on both accounts,
Amazing how little things cna get you: Ref KoKO.
And yes you are correct on pump rotation,
My referance has always been as sitting in drivers seat,
Old airplane thing,
I believe the forums uses passengers side rotation for retard,
now i'm confused,
How do you like the car-code, I,ve had mine for about
4 years, but not using much anymore, Bought a cummins, no programs from carcode for it....
Still have the K3500, having a hard time selling it,
Much better looking truck than any of the new stuff,MHO
Last Item: You may want to ask what TDCD and TDCA
is on most user trucks, If I get a chance I will recheck my numbers for ref:
Doesn't matter whether you're looking at the truck from the rear, and the passenger-side is to your right, or from the front, and the passenger side is to your left, the passenger-side is always the passenger-side - referenced to American soil, of course.
Aussies must interpolate, accordingly.
And, since you cannot easily rotate the Inj Pump from the driver's seat, it is easier to reference the passenger-side as retard, and the driver's side as advance, from your new perspective at the front of the truck, wrenches in hand.
Right, rj?
GMCTD RIGHT !!!! cept I ain't lernd it yet.
23 years AF and a few hours flying, I revert to the
Look out the window, Right thing,,,
How's the other make project????
Bought a 2002 cummins/dodge, still have k3500
can't seem to part with it, no reasonable offers..
Plus it's a better looking truck.....
Second that, rj - might put some flowers in it, make a really nice lookin' planter for the missus.:rolleyes:
Ennyhoo - back to the FSD\PMD thing........
Got the 'scope hooked up, DVM, Tech2 - all in place.
I had previously pulled my 5288 Inj Pump out to donate to a fellow Diesel head, whereupon I then installed a late 5521.
5288 parameters all met factory specs - well, all, exceptin' Base Timing and TDCO, which I had set to +8.5deg and -1.58deg, resp, feeling quite unfettered by EPA mandates.
Mainly, 8-9mm fuel rate, 1.88ms Fuel Solenoid injector pulse width, and etc - right down the middle, all the way.
The engine would cold-crank or hot-crank and run within 1/2 turn of the flywheel - most bystanders wouldn't believe it was an EFI 6.5L TurboDiesel under the old GMC hood.
Life was good.
Then, to help an associate, I swapped out the fully functional IP that GM installed on the engine for the newest, latest production model, the 5521 - the Acme pinnacle of Stanadyne Roosamaster IP wunnerfulness.
I had previously pulled the PMD off it to replace the failed one on the 5288, so I installed it back on the later IP, as per GM and S recommendations
Installed the DSG gearset, dialed it in, hit the start button, and engine fired right up - except, took a couple full revs of the flywheel.
Checked the parameters, +8.5deg Des\Act, -1.50deg TDCO - all looked good except FS injector pulse width was steady at 1.94ms.
Spec sez 1.88ms max, s'posed to fail at 1.94ms, kick out DTC36 @ 2.5ms - but no IP DTC's, no Cyl imbalance DTC's in the log.
Just the long start sequence - 2-3 complete revs of the flywheel.
Pulled the hot-chip outta the PCM, installed the oem tune - same thing, hard-start - and this is summer-time, and the starting is easy.
Or, was it 'and the living is easy' - no, wait, that's another tune, from the late '50s - never mind that.
Anyway, this long-start has continued, in force and unabated, up till today - hot, cold, warm, cool, humid, arid extra dry, don't matter - long start each time.
I thought it may have been that the OBDII PCM's handled the Lift Pump chores a little differently, energizing the circuit at key-on to prime the system during Wait-to-Start sequence - OBDI powers the LP only at START, then with the OPS.
So, I dutifully modified the LP ckt to energize at key-on, during WTS as well as START - still ~2 revs crank B4 run.
Better, but not good.
How embarrasing, to say the least - even my neighbors have often asked if I have remote-starters on my vehicles, as they never hear the starter-motor after I get in and close the door.
So, 'scope in hand, and assorted associated nice-to-have paraphenalia, I decided to run the mystery hard-start down today - 60deg cool clear weather, just right for some cool clear-headed thinkin'.
Connected the test harness, set up the 'scope, plugged in the Tech2, and ready for all comers.
Tech indicating 625rpm, 8-9mm fuel rate, +8.5deg Des\Act timing, -1.58deg TDCO, 178deg ECT, 82deg IAT, 1.94ms Fuel Injector pw
Observed Fuel Inject Control sig on pin A - ok
Observed Closure Ground on pin C - ok, no ringing
Observed Fuel Inject sig on pin E - ok
Scrutinized FS Drive sig on pin F - ok, ringing, -80v spike as expected
Observed FS Ground on pin B - ok, no ringing
Just fer grins, observed +12 source on pin D - holy voltage-drops, Batman!!!!
That's supposed to be a stable power source for the FSD\PMD, but I'm seeing a +3~4v drop to +10v at each FS drive event, with system voltage at +14v.
Hmmm - flip Tech2 to Inject pulse width screen for the usual 1.94ms.
Jumper pin D directly to the battery, watch pin D on the scope, no more trapezoidal-wave signal.
Tech2 now indicating 1.84ms fuel injector pulse width - everything else stable, no changes.
Hmmmmm.........power-down, wait a bit, hit START - VOILA ! ! - half a crank revolution and the engine fires right up, jes' like B4!
And again.......and again........and.......but seemingly, methinks I do tend to belabor the point.
FYI, folks - with Fall\Winter climes quickly upon us, it would behoove those with an EFI 6.5L TurboDiesel to go thru the connections and grounds in the engine bay, do a little winterize tighten-up routine-ing to ensure your vehicle will start and run, and get you there and back.
Voltage sources are only as good as the connections and grounds.
I tried to build the harnesses in my conversion to closely emulate the donor OBD1 trucks, but there must be some harness differences between OBD1 and -II, as most with OBD1 who have upgraded to the 5521 Inj Pump also indicate longer-crank or hard-starting symptoms after the upgrade.
I posted my LP ckt mods, and results were as indicated with mine - about 1 revolution cranking improvement.
So, that's my story, and I'm stickin' to it - and hope to improve it, even further.
Ever since my IP was replaced ~2yrs ago my fuel sol. closure times have been around 2 ms - I've read on here elsewhere that the newer pumps seem to run a little longer. What I do notice is that the closure times seem to be lower with a colder eng. - could this be related to voltage somehow? I've tried both the PMD and a remote mount, with the same effects. I get a 1216 code though, response time short.
gmtcd, sounds like your using a oscilloscope - forgive my ignorance, but how would you check the FSD pin voltages with the engine running without one? I have a multimeter.
Thanks. Joe.
moondoggie
10-23-2006, 10:12
Good Day!
As always, gmctd, rock-solid info, right to the REAL source of the problem. Two questions:
Where did you ground the scope? In other words, what's the reference point for your scope work?
Any chance of rigging it up like before you fixed it & getting some DVM DC voltage readings between, say, the driver-side battery positive terminal & the B+ where it enters the FSD? This would allow us with DVMs, but no scope access, to monitor this voltage drop - it likely would predict whether this is a problem with an individual truck or not. (Seems like a great place for an old-fashioned ANALOG meter. The combination of this solenoid firing @ ~ 10 Hz @ idle, & the DVM taking 30 or whatever readings a second, might simply make the DVM jump all over the place. An old-fashioned analog meter would do a nice job of averaging this all out, eh?)
Blessings!
My 72" extender cable plugs into the Inj Pump harness at the FSD\PMD connector.
The 24" test cable is tee'd off a 3" male\female adapter which is inserted between the IP harness and the extension harness, allowing readings at the oem PMD connector.
Each test point, excepting the system ground, is resistor-isolated from the signal, as I found that merely moving the 10m scope probe between the pins caused hesitation\missing, even killing the engine - restart was immediate with the probe in place, so the test board was reworked for isolated test points.
The ground point for testing is from the black FS ground wire on the IP - I also brought out the Closure Ground wire which separately returns to the PCM, also resistor-isolated to the TP
A DVM on the +12v pin will indicate system voltage, but is erratic, indicating it is not stable - if the DVM has manually-selectable ranges, the symptom is easier to observe in the 20v range.
The voltage can be up to +14v, depending on alternator output, but it is the switching component you will be interested in.
The auto-switching DVM's may not function well, as internal sample-time can add further averaging to the signal.
Switching the DVM range from DCV to ACV will indicate the average p-p voltage of the switching-induced signal on the power bus - the 2v range may work well here if your system is not as noisy as mine.
Joe, it would be helpful to be monitoring the FI pw figure at the time the response time short DTC occurs
moondoggie
10-23-2006, 11:50
Good Day!
"A DVM on the +12v pin will indicate system voltage, but is erratic, indicating it is not stable - if the DVM has manually-selectable ranges, the symptom is easier to observe in the 20v range." Please forgive my lack of clarity. What I think might be useful to folks like me would be to measure from B+ (battery voltage, presumably at the driver-side battery positive terminal) to the B+ at the FSD. In a perfect world, this would of course be 0V. I thought there might be a chance of picking up an average DC voltage that would be useful in determining the degree of quality of the B+ connection between a solid B+ source (again, perhaps the driver-side battery + post) & the FSD. There will of course ALWAYS be some voltage drop between these points; I had hoped that perhaps knowing the difference between your previous situation & now would be helpful to the rest of us.
It occurs to me that maybe this wouldn't work anyway. The 4V sag you saw in B+ @ the FSD is likely of such a short duration that even though it causes the problems you saw (long crank time, 1.94mS inj pulse width), it's duty cycle is probably so small a DVM or analog meter will barely (or not at all) provide a measurement.
Blessings!
(signature in previous post)
Your suggested procedure would be more workable if our vehicles were assembly-line production duplicates - I think indications from my truck would probably not give you much to work from.
Possibly I will have opportunity in a few months to take readings from production '95, '96, '98, and '00 trucks to determine any differences\similarities.
The ac component would be in the frequency range of 40hz at idle - 625rpm/60 x 4 comb events\rev - most DVM's will indicate p-p voltage of frequencies to 10k.
You should have no trouble reading any switching-drop on your DVM.
moondoggie
10-24-2006, 09:59
Good Day!
"Possibly I will have opportunity in a few months to take readings from production '95, '96, '98, and '00 trucks to determine any differences\similarities." That would be most useful.
I wonder how many folks are aware we're getting all this help from a guy (gmctd) that doesn't even have one of these trucks anymore? Mondo gratitude, dude.
Blessings!
signature in previous post
Not entirely true, my friend - the GMC in my sig, which is the '74 body-style, was the recipient of a '95 GMC EFI 6.5L TD in the fall of '99, meant to be a test-bed for some ideas I had at the time.
At least one didn't pan out, but the truck did, and that is the reference for my posting(s), altho I did do some comparo on TBO's '98 OBDII truck.
I recently decided to pop the hood and get up close and personal with the TDCO timing conundrum, and this incident of increased fuel injector pulse width.
It will stop when I know, or when they pry the 'scope probe(s) from my cold, dead, fingers...................
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions Inc. All rights reserved.