No overdrive after injection pump swap

[Tatlocktim]

Hey everybody I got a garage to switch the injection pump in my 93 Sierra because it wasn’t starting after the engine was warmed up… they were able to swap the injection pump, but it will not shift into overdrive now. The Tcs has been adjusted and swapped out. I’m new to the code reading on these trucks… but I think it’s telling me 12, 21 and 85. The garage that returned it to me figures there must be a faulty wire somewhere. I’m gonna check all the grounds for now . My next step will be to take it to gmc dealership:/ anyone ran into this issue?

[Robyn]

Hello
Welcome to The Diesel Page

The Codes
12 means that the computer is able to do a self test.....
21 is throttle position voltage is reading too high (Greater than 4.9 volts)
85 is an "Unexpected gear ratio"

If the rig was driving fine before the shop worked on it......MY FIRST SUSPICION .would be either the THROTTLE POSITION SENSOR is incorrectly adjusted or faulty.....

Here is the procedure to set the TPS

Turn the key on, don't start the engine.
With a voltmeter, check the voltage across the dark blue and black
wires of the TPS.
It should be .5 to .75 volt at idle and 4.2 to 4.5 volts at full throttle.
If the readings are off loosen the screws and adjust the TPS until you get
it in range.
If it will not set in those ranges you may need a new one.

Adjusting is easy....Loosen both screws on the TPS just so you can rotate the TPS in the screw slots....Get a reading with the throttle closed..(Make sure the fast idle solenoid is disconnected before adjusting......If the solenoid is opening the throttle it can mess up the reading)
Check the full throttle reading....With the pedal on the floor....4.3 VOLTS is a good reading.
Then recheck the idle reading.... .5 volts is perfect.....If you can't get both ends of the adjustment to come in....BAD TPS

If the shop installed a new TPS.....These can be junk right out of the box from the average parts house

An AC DELCO part is what you want.......Aftermarket stuff can be hinky.

Or the shop did not adjust it correctly .....

A VOM and a few minutes under the hood will tell the story.

Set the TPS

Disconnect the batteries for a few minutes to clear all the codes.

Restart and see what happens.

The code 12 should be there.....Just says..."I am doing my job"
If 12 is all that's there and no SES light.....Test drive and see if all is well...


MY GUESS AS BEFORE....Shop did not do it right....Or a bad TPS.
I am not sure (Been many years since I have worked on a 93) but the TPS may be installed wrong......The TPS is connected to the throttle shaft and rotates as the throttle is moved.
The computer will start complaining if the reading exceeds 4.9 volts at full throttle...or at any time.....

So get a helper and a good VOM and check the readings.

The procedure above will get you the info you need.

The TPS is held onto the RH side of the injection pump with two screws and it connects to the throttle shaft ...."Slips on"

The TPS is what tells the computer what the throttle is doing.....and where it needs to set things like transmission line pressure....When to shift gears.....
The DTC 85 In my opinion sort of confirms that the this may well be an adjustment issue or a bad TPS
Get it fixed....The TPS settings control the transmission ..... and issues can lead to tranny failure

Good luck....Let us know what happens

Robyn

[DmaxMaverick]

How many miles on the tranny? Overall and since the last service? Check the ATF condition on the dipstick. Fluid should look/feel/smell fresh. If not, or if it's been a while, a service is in order. If the fluid is dark, stinky, and/or feels grainy, it may mean overhaul.

DTC 85 can mean 3rd gear slippage, which will prevent shifting into OD. If Robyn is correct, and the TPS is faulting, low clutch apply pressure can allow the slippage. You only get to continue this condition for a short period before the clutches start going away. Address DTC 21 first, and cross your fingers. 85 may clear once 21 is in line.

[Robyn]

I agree with Maverick 100% TPS issues that result in low clutch apply pressure will ruin the gearbox really quick.....Now the DTC21 shows a high voltage signal (Above 4.9 Volts) The full throttle reading should be 4.5 V

I am not sure what the excess voltage causes....Likely it will cause max line pressure....Too low of a signal voltage is on the opposite end of things and can result in very low pressure.

Best plan is to get the TPS values where they need to be......

I too think that once the value are spot on the DTC 85 will go away....

[Yukon6.2]

With it being a "93" is there a chance the wrong pump might be causing grief?
It should be a manual pump on a 93,but sounds electronic,so could it be a late model 93,which would put it in the 94 year with electronic pump.

[Robyn]

1993 had the 4L80E tranny....Hence the TPS.

It is a simple (Relative term) The ECM runs the Tranny and the emissions system..

1992/1993 were the first 6.5 engines and used a DB2 IP....
Computer needs to know what the throttle is set at to be able to control the tranny.

Back in the good old days....The 6.2 trucks with the TH400 tranny had a Vaccum switch that controlled the vacuum modulator....Sort of a Vacuum TPS.....

The 92/93 were transition years...Sort of....Part mechanical, Part electronic......
The fuel injection is all mechanical...Just a DB2 with a larger plunger volume.
They ran the slightly lower pressure of the 6.2 rather than the high pressure of 6.5 with the DS4 PUMPS...

The 92/93 6.5 had the 4911 Pumps.....Who knows what is on it.....That will not cause the issue.

Setting of the TPS will.... The 6.2 IP will not deliver the fuel a 6.5 can burn....But it should work OK..

[Tatlocktim]

Thanks for the reply Robyn as the guys at the shop we’re trying to figure it out… they said they even took the tps from the injection pump that they took out… and tried it. As the truck was shifting perfectly before. I will definitely check the volts on it and get it dialed in!

[Tatlocktim]

I believe there is 300000 on the tranny … but I’ve only owned it from 290000 …whoever owned it before me took very good care of it.

[Robyn]

Keep us in the loop.

Since it worked before the shop messed with the Pump....Gotta be something they fooled with.

Look over the electrical plug on the TPS....Make sure the wires and connectors are in good order.

NOW

The shop had to remove the intake manifold to get the IP off..

At the Passenger side rear of the intake manifold near the firewall where the main wire harnesses are locate....THERE ARE SOME GROUND WIRES THAT FASTEN TO THE INTAKE
Search that area out well and make sure those wires are connected and none are broken off the connector....

A missing ground can cause all manner of misery .....

And it will screw things up......

These grounds usually connect to a stud topped bolt at the rear of the last intake runner......
These are large ring type connectors ....some of these had built in star washers....

Check this....

[56pan]

No ECM on the '93's. Sure of that. Only a TCM. And an out of adjustment, or faulty, TPS will keep the TCC from engaging. Agreed on that one. Had it happen on my '93.

[Robyn]

YESSSSSSSSSS....TCM..... My bad.....its a computer

I do believe there is a modest ECM as well that handles emissions equipment.

Not sure if this truck is a 1500 /2500 /3500...Not stated

Either way if the grounds were not reconnected or are broken.... issues can happen.

Whatever happened....it happened during the process of swapping the IP

Owner stated NO OVERDRIVE

This final shift which is the TCC as you stated is confused by many as the OD......

I did consider this.....but the big picture is to figure out why the DTC 21 and 85

The 85 (Unexpected ratio) could certainly be caused by the TCC not locking when it should .....At least not without intervention such as the brake switch being opened ......

Be interesting to see what shakes out on this..... I still think it is a simple issue....Adjustment....or a ground not connected or a broken wire...

The issue is not likely to be anything outside of the under hood area that was worked on.

So many shops are in a sweat to get stuff out the door......AND THEY GET SLOPPY.....

[56pan]

"AND THEY GET SLOPPY" Yeah. Just my .02, but I believe it's something to do with the TPS being bad or put on and not adjusted correctly.

[Robyn]

YES THEY DO GET SLOPPY

I agree on The TPS....

The ground wires on the rear of the intake are very important...If they are not connected ....Electricity will find a way....And the micro electronics does not like that game at all...

This is why I mentioned the ground wires...

Will be interesting to see what shakes out....

[Tatlocktim]

Update…. Got the TPs set to the required voltages. .52 at idle to 4.3 at full throttle… then unhooked the batteries. Checked the codes and found that code 21 and 85 were not showing anymore I got excited!!! Took it for a spin and found that it wouldn’t shift out of first now…. Upon return I checked for codes and it tells me code 81 now???

[Tatlocktim]

Truck is a 2500…

[JohnC]

Are you absolutely sure it's in first? Second is the default failure gear of choice. DTC 81 is a solenoid fault. Often that's caused by low voltage to the solenoid(s). One of the fuses should be labeled "transmission". It may also be the instrument fuse. Check the voltage on that fuse. If it's low when you first turn the key on the TCM will lock the trans in second gear.

[Robyn]

I think that for a while we need to be careful and NOT CHASE THE WIND.

A bit ago the only thing wrong was no overdrive (I actually think we are seeing a lack of Converter clutch lockup as mentioned by 56pan)

So.....The TPS is adjusted and then we see a DTC 21 pop up.......

The only change was the TPS adjustment......So why would we start chasing other possibles.....??????

The DTC 21 should have been there.....Changing the IP does not cause all manner of other things to just up and fail....UNLESS the folks working on it got rough with wires and connections and broke something ....OR FORGOT to reconnect something....

ARE THE GROUND WIRES AT THE REAR OF THE INTAKE MANIFOLD IN GOOD ORDER ?????

We need to trace back what was done under the hood....and the possible parts that were handled.....

Sloppy techs can create far more issues than they fix...

From ONE issue to another after messing with the TPS
A HINKY TPS comes to mind

If the TCM (Computer) sees bad input it will go into limp mode and give Reverse and 2nd gear.

This is designed to save the tranny from destruction ......

NEW AC DELCO TPS....Adjust to specs
Be sure the grounds at the rear of the intake are good.
Inspect all the wire connections that may have been fooled with...

Clear the codes....Retry

[DmaxMaverick]

Another thing to consider is battery voltage. Low or inconsistent system voltage can create all kinds of havoc. A failed or failing battery or poor connections are commonly overlooked. One failing battery or one poor connection can hide until it takes down the entire system, or kill a battery or batteries. Batteries should be tested independently, disconnected from each other and the system. Cable terminals should be checked/cleaned, or simply replaced if they are old. The cables can fail internally (corrosion) while looking perfectly fine on the outside. The factory cables (and entire electrical system, for that matter) are marginal when they start life, and they don't improve over time, and as we've seen time and again, clean, proper grounds are essential to a healthy system. I've seen many times over the years, intermittent or persistent problems that (mostly dealers) cure, at least temporarily, by throwing parts at a them. Often, for example, when a problem is rooted in a cable connection issue, simply removing and reinstalling them will refresh a connection, until the next time. Most powertrain repairs start and end, with messing with with battery and ground connections. One poor connection can have you chasing wild geese, for years.

[Robyn]

What Maverick said.......That is the real deal for sure.....A problem surfaces and a bit of random fiddling and the problem goes away....For a while.

As I mentioned....System grounds that many times get forgotten when reassembling after repairs..

[Tatlocktim]

Hey there after I dialed in the TPs and it for a spin it was making it to 2nd not just first(sorry). Then upon returning I got the 81 code… I had to leave for dinner and left it at my father in laws…..2 hrs later …. He phoned me and says he’s got it driving/shifting just fine. All he did was unplug the linkage from the injector pump to the black module on the fire wall and made sure all linkages connected to transmission were attached properly….drove it today and it was driving great! I’m assuming this will reoccur ! Are any of the linkages connected to the transmission prone to corrosion?? Or could it have been the unplugging of the cable to the injection pump?