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So I'm minding my own business and I get a code 88 error - TDC Offset Error..

T

TurboTahoe

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Hi guys!

My Tahoe has been really running well. Today I went to run some errands, and while accelerating, it threw an SES light. It drives normally - no unusual sounds, engine performance, etc. I went home, hooked up my GMTDScan program and read a code 88 = TDC Offset Error.

I haven't changed anything. Just running around town like I always do. No new PCM, no new ECM, no new items at all.

I'm tempted to check my grounds and my fuses. Other than that, I'm kinda stumped as to what could cause it.

What do you guys think it might be?

Thanks,

Rob :)
 
What is your current TDC offset? If your ECM learns a new TDCO that is out of range, it will throw this code. It can happen when your running your TDCO right at the limit.
 
There is the possibility that the TDC OFFSET that was set had taken the servo right near the limits of travel, and a slight bit of wear in the timing chain has occurred, and now the servo can't reach the point it wants too.

Advancing the injector pumps physical location about 1/16" as measured against a reference mark on the timing cover may be all that's needed to get you back into the sweet spot.

The timing is electronic, but the actual adjustment is done with a servo that moves internal parts of the IP

Missy
 
Wow. I am blessed today with answers from two of my favorite forum members!

It was late yesterday when this happened and I (duh) forgot to check what the TDC Offset was set to...

I am guessing that Robyn is right... timing chain has probably worn a little bit, and the servo can't reach the point it wants to.

I will hook up the GMTDScan system and report back ASAP.

Thanks,

Rob :)
 
Hi guys,

Are there any forum members in the Portland, Oregon area who have the tools and expertise to help me fix this TDC offset error? I admit that I think I understand the technical bits, but I don't have either the tools or the experience to adjust the TDC offset setting.

I'd love some help if possible.

Thanks,

Rob :)
 
The TDC offset is a finite number in the computer right now, and will not change unless it's told to.

The likely reason for the 88 is as I mentioned before, the servo can't reach the desired spot.

The vehicle no doubt has had a few pumps on it since it was new, and depending on who installed them, the physical position of the pump can be anywhere within the allowable area in the slots in the IP

Physically moving the IP will not change the timing, BUTTTTTTTTT, will allow the servo the ability to get more adjustment.

For example, if the pump was physically set too far to the passengers side at install the ECM commands the timing to be x and if it can reach it, all is well, if not then it sets the code 88

So your rig was fine and now its not.

A slight stretch in the timing chain and now the crank position sensor reading and whats achievable in the IP by the servo is not matching.

Normally timing chain wear will not effect the timing, but again we go back to the original location of the IP and how much travel the servo has available.

As I said in the PM
just mark the IP AND cover with a straight scribe line and then bump the IP to the drivers side 1/32 to 1/16 inch

Be sure the IP is tight before restarting.

With a nice scribe mark you can get back where you came from without issue.


This issue can work both ways (ADVANCED OR RETARDED) but since this happened out of the blue, the likely hood is that the timing has become slightly retarded.


The nuts on the IP are 15 mm

LOOSEN UP JUST ENOUGH TO GET THE IP TO MOVE.


Missy
 
Thanks Missy for the very thorough instructions.

Here's our status:

1) Put a scribe mark where the IP and Timing cover meet to track how much I have turned the IP.
2) I loosened the three bolts holding the IP to the timing cover. Used 15mm offset wrench and a ratcheting box-end wrench. I did need to move the oil line for the turbo and remove the coolant sensor to get enough room to swing the wrenches on the passenger-side lower bolt. That one's a bear!
3) Moved the IP towards the driver's side by 1/16 inch.
4) Tightened everything back up.
5) Disconnected the batteries for a couple of minutes.
6) Connected everything back up, checked that everything was back where it was before, and connected the GMTDScan software.
7) Even when the engine is OFF (but ignition is on... i.e. the ECM and PCM are active and talking to GMTDScan), I STILL get an error. In other words, even when I haven't started the engine yet! The OBD1 flashing light also shows an 88.
8) Tahoe starts and runs normally still.

I'm stumped. Any ideas? I wonder if the HyperTech chip is malfunctioning...

Rob :)
 
Another couple of bits... If I have the Tahoe OFF, but with the ignition switch in the ON position, and I connect up the GMTDScan software, I read the DTC 88. I then clear the codes, and the GMTDScan software says "OK, codes cleared". I then immediately read the codes again, and I get the 88 again... In other words, the ECM seems to be throwing the code 88 even when the engine is not running, and even after I reset it.

Does the engine need to be running in order for the ECM/PCM to determine if it has a code 88? Or can it figure it all out with everything OFF?

I'm stumped.

-Rob :)
 
NVW said:
Rob, you have to do a 'Time Set' then a 'TDCOffset' learn.
Click to expand...

Thanks so much. I just finished reading this article... http://www.thetruckstop.us/forum/showthread.php?11754-FYI-TDCO-Timing-the-DS4-Injection-Pump

I will probably have to read it a couple more times, but am I correct in understanding that

1) I will need to pick up something like GMTDScan Tech
2) Use GMTDScan Tech to clear the 88 DTC
3) Bring the engine to between 180-195 degrees (Fully warmed up)
4) Use GMTDScan Tech in order Command TIMESET, rpm will increase, engine will hesitate and stumble as PCM determines new IP position, wait ~5 seconds, exit TIMESET
5) Use GMTDSCan Tech to Command TDCO LEARN, engine rpm will again increase, and hesitate\stumble, will self-exit when new value is learned
6) Scan again for +8.5*BTDC ACT\DES IP timing, TDCO at -1.5*

The ECM will then calibrate the base timing according to the changes to the IP that I did earlier and hopefully get the old girl to keep clunking along?

Thanks,

Rob :)
 
Yep, the code 88 will return until you learn a new TDC offset that is within range. You really need to know what it is before you turn the pump so you know which way it says it is out.
 
Knowing what the error is is a good thing, but since you don't have the advanced GMTDCSCAN doing what I described can get you back to a point that the ECM can srt the timing to what it wants to.

Ideally you should do all the diagnostics and see where it is and then go forward accordingly, buuuuuuutttttttttttt, there are times that we just have to fake it.

With the mark on the case/IP you really cant screw it up.

There could be an issue with the IP as well that caused the code to set.

To adjust the IP tad and try it will not hurt anything.

You can't advance or retard the actual timing, but you can get the IP back into a spot where the ECM can adjust it to the value that's currently set in the chip
 
OK, although I really can't afford it, I bit the bullet, and purchased a copy of GMTDScan Tech.

Here's the status and steps taken.

* Put a scribe mark on the Timing Cover/IP base plate.
* Loosened the IP and using a really big channel lock, moved it 1/16" towards the drivers side (left).
* Snugged everything back up.
* Purchased GMTDScan Tech and installed on my laptop.
* Followed the timing instructions, i.e.
Start GMTDScan Tech.
Connect to your truck.
Go into the dashboard view and verify that the engine coolant temp is at, or above, 180 °F. If not, wait before proceeding.
Go into the DTC view and verify that no trouble codes are present.
Go into the TDC view.
Take note of the current DES/ACT/TDCO values. OEM is +3.5°/+3.5°/-0.5°.
Click the TDC Time Set ON button. DES should now read 0° and ACT should read +3.5° on average.
Click the TDC Time Set OFF button to go back to normal operating mode.
Click the TDC Learn ON button. The TDCO value will now fluctuate for about 20-30 seconds before setting itself. You can end the sequense prematurely by clicking the TDC Learn OFF button. The current TDCO value will then be set in the PCM.

When I originally went to TDC view, it read as follows:

Desired Timing / Actual Timing / Top-Dead-Center Offset
8.1 / 8.1 / 0
Remember, this is after I moved the IP, but before I did the TIMESET and the TDCO LEARN.

I then did the TIMESET and TDCO LEARN and got this:

Desired Timing / Actual Timing / Top-Dead-Center Offset
8.1 / 8.1 / -2.02

The car seems to be running well (plenty of power), but rather hot (although it is 98 degrees F outside). My coolant temp briefly touched 212 degrees F going up my hill.

The DTC 88 TDC Offset Error is still coming up, even after I clear it.

What should I do now?

Thanks guys,

Rob :)
 
Go more, your -2.02 is right on the edge. You don't want to be above -1.94 for OBD1 to keep it from coding. Make sure you do the tdc offset learn after you do the timeset so it will take the new value.
 
THEFERMANATOR said:
Go more, your -2.02 is right on the edge. You don't want to be above -1.94 for OBD1 to keep it from coding. Make sure you do the tdc offset learn after you do the timeset so it will take the new value.
Click to expand...

So, just so that I'm totally clear... I should loosen the IP and move the IP a little bit more (e.g. 1-2mm) towards the driver's side?

Thanks,

Rob :)
 
That would be it.

Try to get the TDC OFFSET down to about -1.25 to -1.5
or somewhere close.

Even if you hit it at -1.00 your good.

These can be a PITA to get spot on.
 
If more fooling with things still yields a high minus number (-2.02 example) I would be suspect of the crank sensor doing weird stuff.

The fact that the issue just popped up is always a wonder wtf

See what shakes.

Missy
 
Hi Missy. Yep. I just moved the IP over by another 1/16" and I'm getting exactly the same readings...

First time I moved it 1/16": Desired Timing / Actual Timing / Top-Dead-Center Offset = 8.1 / 8.1 / -2.02

2nd time I moved it 1/16" (Total now 1/8"): Desired Timing / Actual Timing / Top-Dead-Center Offset = 8.4 / 8.4 / -2.02

This says to me that although I have moved the IP a substantial amount, the readings are identical, and yields a high minus number.

Any suggestions on what to try next?

(I guess I've been wanting to buy the GMTDScan for a couple of years now, so that's not all a loss...) :)

-Rob :)
 
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