Timing issues

[arveetek]

My 6.5L in the Tahoe has been acting weird lately when cold. The timing seems to be all over the place. This morning, at 25 degrees, I could barely get the engine to stay running. It started right up, then blew a ton of smoke and died. It did this over and over. When it does run, it sounds like someone has the timing on a knob and is slowly turning it back and forth, from fully advanced and rattling like a Powerstroke to fully retarded to where it will barely run and has no audible diesel noise.

I've noticed it doing this for a while, but it never really affected the way it was running. I'd start it up after work, and it would rattle and then get quiet, rattle and then get quiet, over and over until it reached operating temperature. This morning it was way worse. When it was rattling with the normal diesel clatter, the smoke would clear up and it would run fine. But when the rattle went away, the smoke would billow out the pipe and then it would die. I had to keep feathering the throttle to keep it running.

It's not a fuel issue, it's been doing this on several tanks of fuel.

I haven't pulled any codes.

Any idea on what might be causing this? Does the PMD control timing?

Casey

[joed]

From what I recall, the biggest input to the PCM on timing is the coolant temp sensor (the one located in the crossover toward the pass. side, not the one in the driver's side head).

Have you tried unplugging it completely? If it starts and runs more consistently, either the sensor or the connections to it are likely bad. This should also throw a related code.

An easy thing to check first.

Joe.

[arveetek]

I have done the sensor mod....the sensor is disconnected by a relay until after the engine has been running for a moment...aids in cold starts by extending the glow time and advancing the timing a little...I don't think that's the problem because after the sensor comes on line, the engine rpms drop a little and it quiets down some (or at least used to...) The rpms still drop, but the timing seems to be all over the place.

Casey

[DickWells]

Have you checked your timing chain for wear? You can check it by taking out the oil filler neck and watching the gears for movement down in there while you rotate the crank back and forth with a bar. Could be there's so much slack in the chain that the pump is bouncing ahead and back, thus changing the timing. How much mileage on the engine?
Just a thought, and worth checking I should think.
Good luck.
Dick Wells:)

[arveetek]

Around 205K miles. All stock.

Casey

[DickWells]

Now that I think about it some more, it seems like I used to be able to check down in there and see/feel chain slack. Can't remember for sure, but 1/2 inch kind of sticks in my mind as being the limit. I E if the chain bellies down 1/2 below flat when tension is off and flat being when tension is on, then you have timing system wear. Perhaps those who are still involved with the 6.5 can articulate this a little better for you.
Regards.
Dick:)

[arveetek]

I uploaded a video this morning trying to show what I'm talking about.

http://www.youtube.com/watch?v=sK7A57JklAk

Listen towards the first of the video, and you'll be able to hear the diesel clatter coming and going. Of course, it didn't do it all that bad this morning, and started up pretty normally.

Casey

[arveetek]

I uploaded another video this morning. You can hear the issue better on this one.

http://www.youtube.com/watch?v=ooGMtEUYi3I

It still wasn't as bad as the other morning, and started pretty normally. But you can still hear the diesel clatter coming and going. I then put the vehicle in gear with my foot on the brake and revved the engine a little. I'm not moving, but at one point you can see the speedometer jump up and down in relation to the engine timing moving up and down. Perhaps I have an electrical issue? Alternator problems maybe?

Casey

[Subzilla]

Oh my, Casey! That does sound disturbing! You definitely can hear it in the videos. I'm sorry, I don't have any expertise here. Just offering my hope you find the pesty problem. :(

[DaveBr]

I'm just throwing this out there. Crankshaft positioning sensor. I watched the video and thought what would I check into and this comes to mind. Good luck with your issue.

[Hubert]

Does it do it when its warmed up? Or been plugged in?

Don't know for sure but will venture this.....

Sounds like its the after glow kicking in and getting better combustion during afterglow cycling. At that age all bets are off on crispness of timing, injection spray, and combustion. Might have a weak injector or leaky one that's not combusting well or on time but does with afterglow or something to that affect. Maybe missing and not combusting without afterglow which causes lots of white smoke (cold fuel not burning completely) then preigniting some with afterglow on successive rotations causing preignition and loud rattling.

Try plugging it in for 4-6 hours before a cold morning and see how it does.

I would think a fuel metering issue from the PMD or FSD or the fuel solenoid itself mechanically failing to time injection accurately would cause more idle surge than just rattle differences. It does sound like good fuel metering just differences in combustion timing or affect.

Might can see if you can hear the stepper motor searching or varying time erratically. Unplugging optic sensor will set default time and fuel rate and if rattle still varies then further points to afterglow/injector/glow plug issue.

[Hubert]

Sounds like its the after glow kicking in and getting better combustion during afterglow cycling. At that age all bets are off on crispness of timing, injection spray, and combustion. Might have a weak injector or leaky one that's not combusting well or on time but does with afterglow or something to that affect.

Maybe a little clearer you have some tired nozzles and injectors that are "squirting" and not spraying all that well. Such that atomization is an issue during cold starts. It sounds awful rythmic with the afterglow like with some added heat of the glow plugs the combustion is better probably preigniting left over fuel from previous colder revolutions too.

[arveetek]

Does it do it when its warmed up? Or been plugged in?

.

Thanks for the replies, all.

Once normal operating temperature has been reached, the problem goes completely away. Plugging it in helps some, but it is still there.

On Monday morning, it would run and then start chugging, blowing smoke, and then die, as if the timing was pulled all the way back to where it wouldn't run anymore. It's almost as if the ECM or other electronic control device can't decide where the timing should be, and is "searching" for the sweet spot. I wouldn't think injectors, since it only happens when cold, and I doubt it could be afterglow, since it's so rythmic, and the afterglow has already stopped. This problem will continue for miles and up to 10-15 minutes....long enough to be past a cold injector or glow plug issue.

Where is the optic sensor?

This truck has also had a couple of years of home-brewed biodiesel run through it. However, I haven't used any for a couple of months (lower pump price and low supply of veggie oil). This might be a factor in the optic sensor, or other IP issues.

BTW, the IP was replaced around 40K miles ago. New Dtech PMD late last summer.

Casey

[arveetek]

Some other points to ponder...

It's hard to tell in the video, but the diesel clatter is not coming and going as if a switch were being thrown on or off. It's more gradual, as if a knob were slowly being turned up and down. I don't see how this could be a mechanical problem (i.e. injectors or timing chain). It's gotta be an electronic or sensor issue.

Also, notice how the speedometer jumped up and down in time with the diesel clatter for a moment or two? I wasn't moving yet. That was with my foot on the brake and just revving the engine slightly. No wheel slippage occurred. That's kind of weird, huh? I think that also points to an electrical issue.

Thanks again for any help!!

Casey

[Hubert]

OK if it continues after a couple of minutes of starting afterglow should be complete and not affecting combustion.

The optic sensor plug is on top, front, center ish of injector pump near the fuel shut off solenoid iirc. Not sure how easy it is to get to the plug I haven't looked specifically at it lately. The actual optic sensor is inside in front of the cam ring. In kinda the main cavity of the IP body.

On the speedo jumping up mine does that a little depending and seems like it has done that for a long time (trying to hold just off idle) and I think a some what common / normal 6.5 ghost maybe.

[joed]

I wonder if you have a bad ground(s). This could be varying the voltage to the ECT sensor thereby affecting timing. I think it's grounded at the common ground located at the back of the pass. side head. I would check these as well as the main batt. grounds.

I'm guessing you still haven't set any codes? You may have to run a scanner while driving to really pinpoint it.

If electrical/sensor issues are ruled out, about the only other thing would be the IP - my 98 would do something similar when cold - surge and hesitate and then run fine warm. I checked all sensors and finally decided it was just the way my replacement IP was set up - the fuel solenoid closure times were long, especially when cold. A sticking fuel solenoid would certainly affect timing. I would get FSD types codes when this occurred.

Joe.

[Robyn]

I touch on several things here but the one that seems to me to be quite possible is the Coolant temp switch (read further)

Crank sensor issues will generally toss a code.

Timing chains can get loose but wont cause the hunting.

The speedo bouncing is due to the output sensor being right on a cog in the reluctor.
This is a fairly normal thing and most all trucks can and will see this at times so dont chase a ghost here.

My first suspect is always the PMD but with this issue I am suspect of the IP and in particular the optical sensor and very possibly the fuel solenoid.

A fuel solenoid (Internal one that controls the fuel rate) that is getting sticky or has other issues could possibly do this.

The advance is also a suspect and this brings me to the ***Coolant temp switch****.

Try unplugging the CTS (in the coolant Xover)
If the switch is bad it can cause the advance to come on and off which will make the thing alternately sound like a can of rocks and then not.

With the temp switch unplugged the ECM will think it's real cold outside and set full cold advance and it will stay there.

If the hunting stops replace the CTS

Robyn

[Warren96]

The cumputer knows whats wrong,you have to read the codes.

[arveetek]

The cumputer knows whats wrong,you have to read the codes.

Good advice! :D

Casey

[rameye]

Wow I watched your video...that is bizarre!

I love to see what the timing is doing via a scanner!

Please let us know how you made out......good luck

[DmaxMaverick]

Make sure your IP is tight. Stranger things have happened, and a pump that won't sit still will have timing to match.

[arveetek]

Just a quick update. Haven't had much time to check things out, but I did rule out the temp sensor in the crossover, and the alternator as well (thought it might be messing the voltage up). Unplugging both had no affect on the situation. However, it hasn't been nearly as bad lately since it's warmed up some. Unplugging the temp sensor does advance the timing and speed up the rpm, but the timing "hunting" is still there.

I'll pop the engine cover off and check the IP bolts and other items soon.

Casey

[arveetek]

I've also ruled out the PMD. Swapped it with another one and the same weird timing issues are still there. Also checked pump mounting bolts, and they're fine. Haven't gotten to the optical sensor yet, nor have I had a chance to pull codes.

Problem isn't nearly as noticeable now that the weather has warmed up.

Casey

[arveetek]

I think I may have found my problem. Or at least I found a problem, anyway!

I was changing my fuel filter last night and discovered that my lift pump is not working. I have Kennedy's OPS harness, so I'm able to push the button on the firewall to activate my pump, which is very handy for filter changes. Well, I opened the drain valve on the front of the engine and pushed the pump switch, but nothing came out. I could hear the pump running, but no fuel or water came out of the drain. So then I removed the old filter, and tried pumping some more fuel into the housing. Again, the pump would run, but very little fuel would appear. With the pump running, I could watch the fuel level slowly climb up the inlet tube, but as soon as I released the switch, the fuel would drain right back down.

I've noticed the engine stumbling once in a while, and the power seemed a bit sluggish. I could hear the pump running, so I never thought much about it.

I know the mechanical IP's timing is affected by the fuel pressure in the housing...what about the DS4? Could a failed lift pump cause timing issues like I've been having?

I guess I'll know for sure when I replace the pump in the next day or two.

FWIW, the lift pump was a new AC Delco unit a little over 3 years and nearly 40,000 miles ago.

Casey

[arveetek]

I replaced the lift pump tonight. Now that I think about it, I bet this pump was starting to fail about 11,000 miles ago. That's when I changed the fuel filter last, and that time I had a hard time purging the air out of the system, and the engine stalled a few times before I got all the air out. It acted as if the lift pump didn't have enough "oomph" to pump fuel into the new filter and out of the drain.

This time, with the new pump, I had the fuel filter bled in no time flat, and the engine never even blipped.

Hopefully this will solve my weird timing issues as well.

Casey

[arveetek]

Well, it wasn't my lift pump causing my issues:

http://www.youtube.com/watch?v=gEh3EZfg6Ag

She's been running just fine, and then the other morning acted up again.

I haven't been able to pull any codes yet. All of the generic parts houses code readers won't connect with the diesel computer, and the local GM dealer wants $70 just to hook up their scanner.

However, I did unplug the optical sensor on top of the injection pump, and the engine died. After a hard restart, it idled just fine, and the timing stayed in one place. I then shut if off, plugged the optical sensor back in, and then the problem reappeared.

I guess that means I need to replace the optical sensor?

Casey

[Robyn]

have you tried replacing the filter harness that goes to the Optical sensor??

(has the little black box in it)

If this does not solve the issue then the OS is likely causing the problem.

In watching the video it is obvious that the timing is all over the map from about normal to very retarded (white smoke)

Hate to say it but the IP may be on the way south.

The OS is not something that is normally a owner serviced item.

I would recommend the pump be removed and tested on a test stand and repaired as needed.

I have never seen this condition on a 6.5 before.


Keep us posted

Robyn

[JohnC]

If it's a '95 the only code reader you need is a paper clip...

Optical sensor will show up on the scanner as missed counts.

[Robyn]

A fault with the OS should trip a DTC 17 if its way out of limits.

I spoke with the local Stanadyne boys as I was sitting here.

Likely that the Fuel solenoid is going south.

If the condition tends to get hinky as the glow system cycles it almost confirms it.

The voltage drops radically across the system when the glow system does the afterglow thing.
This condition changes the pulse width enough that it can adversely effect a pump that is on its last legs.

Unplugging the OS simply puts the system in limp mode and the only thing that is used is the crank trigger. All other sensors are off line in this mode.

Now along with the IP the timing chain can be worn and so on.

A whole raft of slight anomalies that have ganged up to cause the
issue.
With a fuel solenoid going south the system just can't deal with it any longer.

Time for a pump Overhaul me thinks.

Just mark the pump with the case and you will be able to get the sucker back on and going with minimal bother.

A bad PMD could cause issue but usually not a cold issue like this.

The stumbles and the power loss is also a ggod indicator.

Pump and squirt time

Keep us posted

Robyn

[arveetek]

If it's a '95 the only code reader you need is a paper clip...

Optical sensor will show up on the scanner as missed counts.


I know, but my CEL light does not function. I suppose I could repair that first and then try to read the codes.

I'm sure a dealer somewhere killed the CEL at the same time they rolled back the odometer! (that's another story)

This IP only has around 40 to 50K miles on it, according to GM service records. Shouldn't they last longer than that?

Casey

[arveetek]

I just spoke with my local Stanadyne shop, and they told me that they had this very same issue on a pump yesterday! They said it did turn out to be the optical sensor. They also said that while I can physically swap out the sensor myself, they don't recommend it, as the pump needs to be calibrated for the new sensor. If I brought the pump in myself, it would be at least $500 for the sensor and calibration on the test stand.

Hmmm...I'm starting to think that MFI is in my future! I'm tired of these touchy, sensitive DS4 pumps.

That darn 4L80E is the only real hurdle....

Casey

[john8662]

This IP only has around 40 to 50K miles on it, according to GM service records. Shouldn't they last longer than that?

Casey

Probably not with a bad lift pump... :rolleyes:

I'd find a good used DS4, like a 5288 or a 5521 and swap it out. You don't have much to lose. You could also just swap out the OS from any pump you find, remember, ebay, they're usually on there.

The DS4 is pretty easy to swap out, as long as you align it close to where the other one was (in relation to the bolts in the slots of the pumps front cover), it usually runs like nothing happened.

I wouldn't pay for a reman pump at this point, there are cheaper options around, and I'm sure you're not afraid to tinker, just troublesome when it's your main vehicle and you don't have a spare (do you?)

Yeah.. Fix the Check light, probably just the bulb, the dash is REALLY easy to take apart to get to the cluster, then just a few bolts and the thing pulls out, bulbs on back...

[arveetek]

Probably not with a bad lift pump... :rolleyes:

Smart aleck!! :D So it's had two lift pumps fail under my watch...am I really to blame? ;)


I wouldn't pay for a reman pump at this point, there are cheaper options around, and I'm sure you're not afraid to tinker, just troublesome when it's your main vehicle and you don't have a spare (do you?)

Well, I just picked up a '97 Jeep Wrangler TJ for a play toy....it may become my DD for a while until I get this sorted out.

I really, really debated about selling my '81....I kept thinking that her super duper 6.2L turbo would make a good replacement engine if my 6.5L ever gave up....but you know how it goes....(or do you ever sell anything? ;) )

So do ya'll think it would hurt to try replacing the optical sensor anyway? I know people have done it. http://www.mamut.net/royh/newsdet9.htm

Casey

[Robyn]

I would scrounge up a good used pump and swap out the fuel solenoid as well as the OS and give it a go.

Or as was mentioned swap the IP out.

Be sure that you use the correct Chip for the IP your using though.

Just swapping the pump can cause issues if the ECM does not like what you installed.

Now this may only apply to the old 5068 pumps, not totally sure.

keep us posted

Missy

[john8662]

You can't user service the fuel solenoid, as Robyn indicated above.

Casey,

Haha, on the selling stuff, yeah, I know, hard to get anything out of them after you've owned them for awhile it seems. Plus I'd actually have to fix all the stuff that's wrong with em before selling to anyone else. I put up with a lot sometimes...

Yep, DD the Jeep, isn't this Jeep #2?

late

J

[arveetek]

Yep, DD the Jeep, isn't this Jeep #2?

J

Actually, it's Jeep #3. I started with a '94 Wrangler YJ, went to a '93 Grand Cherokee ZJ, and now have the '97 TJ. This is just a play toy. I like to go off-roading, and wanted something I could drive on the street as well as on the trails. The ZJ was just a trailer rig...had to haul it to wherever I was going and then hit the trails...that was getting old.

Casey

[arveetek]

Well, it's bad enough now that I can't even keep it running. Haven't driven it all week since it's been nice weather (driving the Jeep with the top off). I tried to start it this morning, and it wouldn't stay running.

Hopefully I'll have time this weekend to tear into it and see what's going on.

What are the chances that the optical sensor is just dirty and that a good cleaning would get it functioning again? I know that there was a lot of gunk in the filter housing the last time I changed the filter....

Casey

[arveetek]

Sheesh, I've been busy lately!

Once the Jeep heard that it was going to be my DD, it decided to act up too....the CEL came on and started running pretty rough. Took a while to track down a bad TPS and some corroded wires at the PCM. Finally got it running right today.

Also today, I was able to get a lot of work done on the Tahoe. I replaced the optic sensor (a.k.a encoder) in the injection pump, and it was a really easy job. I also removed the vacuum pump and put on a shorter belt, as well as install a Turbo Master. She runs much, much better now. Naturally, she's been running fine for at least a week without a single hiccup, so only time will tell if the problem has been solved.

I will say this..the inside of the IP was pretty nasty...really gunky from the Biodiesel I presume. I'm going to have to install a better filtering system. I can see why the optic sensor would fail under such circumstances.

The old Tahoe runs a lot better now...seems to have more power.

I bought the optic sensor/encoder off ebay for $210 shipped.

Casey

[arveetek]

After a month of driving, I'm extremely pleased with the optical sensor change! The old Tahoe is like a new truck, has more power than it's ever had. Runs awesome, and no more timing issues. Seems like I have more "fishbite" than before, but that's probably another issue.

I can actually tow a trailer now! I hauled my Jeep on a 16' flatbed when I went 4-wheeling on Memorial Day. I had no trouble moving down the interstate at 65 mph with the cruise set while in Overdrive. Not too shabby for a 1/2 ton vehicle with stock programming and 3.42 gears. Before when I tried to tow with this rig, it was pretty much a joke. Now with the new optical sensor and Turbomaster wastegate, life's a dream!

Casey

[arveetek]

I've put nearly 10,000 miles on the Tahoe since I swapped out the optic sensor. It's still running great, better than ever before the swap, actually. I'm really pleased.

We went to Branson this past weekend. On highway 65 south between Springfield and Branson, there are several long, steep grades. Always before, the Tahoe downshifted into 3rd in order to maintain speed. This time, after the optic swap and Turbo Master, I was able to maintain 70 mph in OD up every grade...it never downshifted once. I was passing lots of gas rigs who probably didn't want to push too hard and suck the gas down. I flew by them around 2000 rpm in overdrive, with about 9 lbs of boost and very little smoke. I was really pleased!

Casey