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

[THEFERMANATOR]

Looks to me like your going the wrong way. IIRC desired should be 6.5 during time set for a decent TDC offset, looks like your going the wrong way.

 

[ak diesel driver]

Going to the drivers side advances

 

[TurboTahoe]

Hi guys,

According to this post by GMCTD from way back: http://www.thetruckstop.us/forum/showthread.php?11754-FYI-TDCO-Timing-the-DS4-Injection-Pump&p=144944&viewfull=1#post144944
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If initial scanned TDCO value is elevated to some level greater than -0.5*, this may indicate BASE timing is not +3.5*BTDC

In this case Command TIMESET, exit; command TDCO LEARN, rescan TDCO - if same value, you will have to punt: either

- move IP to exacty vertical and do the standard setup

- or move IP 1mm to right, do TIMESET and TDCO LEARN, scan for new value
repeat at smaller increments until desired TDCO value is attained - PCM will DTC for TDCO over-range at some value greater than -2.02* for OBD1

*Again, aftermarket tunes seldom comply, but TDCO values at idle always represent Base timing, if you interpolate after the initial scan:

-0.5* = +3.5*

-1.5* = +8.5*

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So, if I understand this correctly, then I need to loosen the pump and move the IP to exactly vertical and then do another TIMESET ad TDCO LEARN.

Does that sound right?

-Rob

P.S. Thanks to all you guys for chiming in. I really appreciate your expertise.

 

[THEFERMANATOR]

I would start there and then adjust accordingly to get your TDC offset correct. Just keep in mind, SMALL adjustments make BIG changes.

 

[Missy Good Wench]

As I mentioned, if you keep getting the same -2.02 it may be the crank position sensor that's doing weird crap.

There is the possibility of an issue with the IP as well

 

[Missy Good Wench]

My one concern is why the TDCO all of a sudden changed to where the thing started complaining ????

The value stored does not just change by itself.

 

[Missy Good Wench]

Reading through the manual and the various posts.

Try adjusting the IP back towards the pass side a bit beyond your scribe mark.

Warm it up good, then do the time set.

You want to see numbers in the 3.5 range and here your TDCO should come into a more reasonable range

If you get the TDCO down in an area below the -1.9 some, call it good and button it up.

If you can hit a -1.5 that would be sweet.

 

[Missy Good Wench]

The way we have been going is doing what it's supposed to, THE TIMING IS ADVANCING
We need to get the timing back to a number closer to 3 to 3.5 and see wasssssup.

Missy

 

[TurboTahoe]

Thanks Missy, I appreciate all your research and good advice. Thanks also to TheFerminator and AK Diesel Driver. You guys are great!

OK, I will put the IP back to "Vertical" and do a "Standard Setup" of TIMESET and TDCO LEARN after all is warmed up.

I agree that "something happened", which might be a failure of the Crank Position Sensor (CPS) or something else.

CPS is about $40 from my local NAPA (Their house "Ecklin" brand)... although getting it out might be a pain.

I will start with moving the IP back to it's 'starting position' and report back.

Thanks again,

-Rob

P.S. I used to have a '99 Factory Service Manual, but I sold those along with the Suburban... lots of things changed from 95-99 so it only applied to my 95 Tahoe like 50% of the time anyways.

 

[THEFERMANATOR]

The TDC offset will relearn every 50 starts or so as the ECM is programmed to do this to compensate for wear in the engine and variances in the sensors. So it can go out of range if it was close to out of range to begin with. Or it could easily be a bad crank sensor, optic sensor, stepper, or an IP crapping out. First go in and do the time set to get down to the 3.5 range the ECM wants to see, then do the TDC offset and see if it comes into range then. You want to be around -1.0 to -1.5 for a good compromise of power and keep the engine as quiet as possible. Many flirt and set it at -1.94 to -2.0 and the code 88 can easily happen in this instance when it does a relearn after 50 starts.

 

[Missy Good Wench]

I agree 100%

If you get the timing back to the 3.5 and it still does not want to quit giving the TDCO at -2.02 or, then we need to suspect other items.

How many miles on the IP ????

Missy

 

[TurboTahoe]

OK, I think I got this fixed... for perhaps 50 starts...

Here's what I did:

1) I moved the IP to vertical, scribed a mark to indicate vertical, then bumped it 1/16" towards the PASSENGER side.
2) Did TIMESET and TDCO LEARN. Result: Desired/Actual/TDCO Offset = 9.0/9.0/+2.02
3) Figured I went too far... so I moved it the other way... 1/32" past vertical, towards the driver's side.
4) TIMESET and TDCO LEARN. Result: Desired/Actual/TDCO Offset = 9.0/9.0/-1.94

I was then able to clear the DTC 88 code, and it stayed OFF.

Took her for a test drive, and everything seems OK now!

Here's what I theorize happened:

A) Likely some kind of wear occurred, perhaps the timing chain. This caused the adjustment mechanism for TDCO Offset to fall out of range. Which direction I have no idea.
B) At the 50th key start after the wear went past the adjustment limit, the ECM performed it's usual TDCO Offset LEARN, and it coded a DTC 88 error when the TDCO LEARN gave a reading that was out of range.
C) Here's my mistake... I attempted to correct the IP without knowing what the TDCO Offset was at time of the error... mostly because I didn't have any scan software. By doing so, I didn't hurt anything, but I had no idea what the previous reading was. I SHOULD have purchased the GMTDScan Tech software in order to do a TDCO LEARN and read the offset BEFORE any adjustments. At any rate, I now have no idea what the reading was that caused the error - whether it was too high or too low. Now I'll never know. In addition, there is no way (that I know of) to force a TIMESET and TDCO LEARN without having scan software.
D) By adjusting the IP back and forth (AND having the GMTD Scan Tech software), I now know how a very little change in IP angle can generate a very large change in TDCO Offset, and I know what's happening as I move the IP back and forth.

It is running fine now... although I am thinking about bumping it back towards the passenger side just a tiny bit to see if I can get it to around -1.5

I'll report if anything else weird happens.

A BIG THANK YOU TO MissyGoodWrench, The Ferminator, and AK Diesel Driver for all the help. You are all the best!

-Rob

 

[TurboTahoe]

I agree 100%

If you get the timing back to the 3.5 and it still does not want to quit giving the TDCO at -2.02 or, then we need to suspect other items.

How many miles on the IP ????

Missy

I'm not really sure how many miles on the IP. I bought the rig with 153K miles, it now has 198K. I know that the service history showed that the IP was replaced sometime before I got it but I've lost my notes... A guess is that it likely has around 80K on it.

I have been running B99 biodiesel in it, hopefully that's kept the innards well-lubed on the IP. I know that I have zero blowby.

-Rob

 

[Missy Good Wench]

The Bio can create issues with the DS4 PUMPS

You are running 99% bio ???

 

[TurboTahoe]

The Bio can create issues with the DS4 PUMPS

You are running 99% bio ???

I have run B99 for the last 10 years, and it has never caused any issues that I know of. I purchase commercial ASTM-certified B99 from Sequential Biofuels here in Oregon. I also used it in my Suburban before I sold it. Total I have run B99 for around 100K miles with zero issues. The only thing I do is to mix it with regular diesel during the winter, and I dilute it to B50 or B20 depending on how cold it is.

In fact, the card lock I usually frequent has just stopped selling B99, and I'm sad, because the vehicles really run quite well on them, smooth, (relatively) quiet and good power.

I have never found any issue over the last decade that I can attribute to running B99. Both rigs have received regular maintenance, in excess of what the owner's manuals call for, e.g. Engine Oil and Filter changes every 3K miles, usually with Delo 15/40 and a Fram HP4 filter.

Component failures have been really normal: Lift pumps, Oil Pressure Switches.

In fact the only possible thing I can think of regarding the B99 is that I needed to swap the fuel filters out every couple of tankfuls when I was first ramping up on B99. I did it over like 4-5 tankfuls.. B20/B50/B80/B99, and I had to swap out the fuel filters twice as I recall. Now that I have been running B99, the fuel filters stay very clean, and the rig runs very smoothly.

What kind of issues does the B99 cause with DS4 pumps?

Sincerely,

Rob

 

[TurboTahoe]

OK, based on all the good advice here, I did one final adjustment. The TDCO value is now -1.5. No codes, running just fine. I'm stopping.

Thanks again for all the quick responses and gracious advice. You guys are really wonderful!

Sincerely,

Rob

 

[Missy Good Wench]

Great :thumbsup::hello:

Now, just for the records, what did you do??

This will allow anyone else who comes along to be able to duplicate your remedy.

What did your timing wind up at ???

A TDCO of -1.5 is a great spot.

The engine will rattle a bit harder when its really cold, but it's still a good compromise.

The 94 Burb I did the engine on was at -1.8 and on a really cold start (single digit to teens) would make a powerstroke blush, Gawd that thing would rattle.


Missy

 

[ak diesel driver]

Tdco can be set by doing the KOKO method. With out a scanner you have no idea where its set tho...

 

[Will L.]

On the bio fuel: It all depends on the mfr/supplier/fuel makeup. A bunch of the plants will use additives or cut the fuel to hit the flash point requirements that will effect the cleaning properties of the fuel. Think using old low grade unleaded vs fresh 103 and using them to clean parts.

This is a somewhat common problem of washing your fuel tank and lines clean with the fuel- it cleans everything and deposits that material into the filter. A bunch of people see the dirty filter and blame the fuel right off. When I worked at 1 large fuel supplier here in Vegas and they started using it we saw some of the company owned gas stations experience it. After the first few filters are gone then everything stays clean because the build up in the tank and lines are now gone.

When we did initial test runs with peanut oil there were some unhappy results that were simple chemical fuel problems that did not end well for many a engine. Had nothing to do with cleaning all to do with the composition of the source. So it is not always a case of it will get better. A modified version of tried and true is my theory on it- Tried on someone else's dime then my rig can stay true.

There is a lot of argument about lubricity gains/losses on bio. Truth is there all over the place. Any company can mix their batch to do one thing on Monday and something completely different on Tuesday.

When it comes to fuel testing there are tons of companies all over the place to test for multiple things, but there are only 2 labs that are fully accredited that are accepted by all the refineries and our last batch of tests that went through one of those two were $20,000 per run. Yuppers $10,000 per gallon. We get a discount. Disregard any testing you can afford to do yourself for "full testing"- they are stretching the truth a tad. You have better test results than most people can hope for in time and miles. Keep doing what your doing. Commercial bio fuel is regulated WAY tighter than conventional fuels and believe me-A LOT MORE can go wrong with fuel coming out of crude less than sweet. Most people don't realize there are more bugs in convention fuel than there is in bio fuel. Yes folks Hydrocarbons support life. Most of the hydroscopic fighting agents in crude pump is not because it is hard to separate water from oil- it is to kill critter.

Everyone just keep recycling your plastic please, it will be helping your fuel tanks more soon, if not now for some of you with out even knowing it. That's another story in the works.

 

[TurboTahoe]

Great :thumbsup::hello:

Now, just for the records, what did you do??

This will allow anyone else who comes along to be able to duplicate your remedy.

What did your timing wind up at ???

A TDCO of -1.5 is a great spot.

The engine will rattle a bit harder when its really cold, but it's still a good compromise.

The 94 Burb I did the engine on was at -1.8 and on a really cold start (single digit to teens) would make a powerstroke blush, Gawd that thing would rattle.


Missy

OK, that's a good question. Let me recap. Please correct me if I make any factual errors in my description.

What to do if your 6.5 diesel has a "Service Engine Soon" light with an 88 TDC Offset Error.

1) The rig threw a DTC code of 88 TDC Offset Error.

2) Why did the engine throw this code?

Context: The simplistic way that I think about this is that the injection pump needs to know "where" Top Dead Center (TDC) is in order to properly inject fuel into the engine at the correct times. TDC refers to the exact point when, during the compression stroke on a 4-cycle engine, the piston is at the very apex of the compression cycle, the so-called "Top Dead Center", or the maximum compression point. The 6.5 Diesel engine does this by relying on a mechanical system that is tied into the timing chain of the engine, which is directly coupled to the rotational position of the rotary DS4 injection pump.

So why the "88" error code?

This means that the engine auto-set the "Top Dead Center" (TDC) Offset and the offset was beyond what is considered "Normal", i.e. between -2.02 degrees and +2.02 degrees off TDC. I hypothesize that this happened because of wear within the engine (possibly timing chain wear). The 6.5 diesel will perform what is called the "TDC offset LEARN" every 50 start cycles in order to accommodate for changing conditions and engine wear. In this particular case, the engine performed the "TDC Offset LEARN" and the offset was beyond normal range, so it threw the error. This is the engine's way of saying "I ran the TDC Offset LEARN algorithm based on current conditions of wear, etc., but the offset required is beyond my ability to automatically correct it. You need to correct this condition manually." Thus it sets the "Service Engine Soon" light, which, as the name of the light implies, means you should do something about this soon, but the engine will keep running fairly normally in the meantime.

In this case, the wear of the timing chain and associated mechanical bits had progressed to the point where the injection pump (IP) needs to be manually moved in relationship to the rest of the system in order to correct the error associated with wear. I suppose a really crude analogy might be that you need to manually adjust an auto belt tensioner in order to compensate for a stretched or wearing drive belt, where the spring tension on the auto belt tensioner isn't enough to take up the slack on a worn drive belt.

3) What do I need to fix this normal wear problem?

Assuming that the problem is indeed a normal wear problem where adjusting the IP will fix the problem, here's what you need to do.

You need a 15mm offset box wrench, a 15mm combo wrench, and ideally a ratcheting 15mm box-end wrench.

In addition, you MUST have a copy of a decent computer diagnostics/scanning program. My engine has GM On-Board-Diagnostics version 1 (OBD1), so I chose to purchase the excellent GMTDScan Tech program, http://www.gmtdscan.com/. You may need something else. You CANNOT get away with simply using a code scanner from the local auto parts store. You need a diagnostics package in order to force the engine to issue TDC TIMESET and TDCO LEARN commands, in addition to reading the timing values that are stored within the Powertrain Control Module (PCM). You will also need a USB-to-ALDL Interface Cable, which is different between OBD1 and OBD2. You can buy these from different online vendors.

In order to fix the problem, you basically have to A) read the "Desired Timing / Actual Timing / TDC Offset" (DES/ACT/TDCO) values with your scanning program in order to decide which direction to rotate the IP, B) Loosen and Rotate your IP in the proper direction and the proper amount and C) confirm that you performed B properly with the scanner software by issuing TDC TIMESET and TDCO LEARN commands and reading the resulting values.

I made the mistake of NOT buying the scanner software before I started adjusting the IP. This is a mistake because without some way to read DES/ACT/TDCO and issuing TDC TIMESET and TDCO LEARN commands I was not only flying blind, but had no way to force the engine to recognize what I had done to the IP.

4) What exactly did YOU do to fix the problem?

I basically followed the guide from the GMTDScan FAQ, which is repeated here with a bit more detail:

•*Start GMTDScan Tech on your PC Laptop. Connect the interface cable to your OBD connector and an open USB port on your laptop.
•*Use the GMTDScan software to create a communication connection 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. This is a little tricky, because when you have a DTC 88 error, you really can't get this to clear out. I think that the issue is that you don't want any OTHER DTCs to be set which might mess up the calibration (i.e. the TDC TIMESET and TDCO LEARN). For example, if the engine is in "limp mode", this would just make things worse.
•*Go into the TDC view of GMTDScan
•*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 sequence manually by clicking the TDC Learn OFF button. Whatever the currently displayed TDCO value will then be set in the PCM.
•*Once you know the value, you know which direction to turn the pump. Towards the drivers side is "+" and towards the passenger side is "-". A 2mm move equals 5° so take it very easy and do not attempt to turn the injection pump while the engine is running!
•*Scribe a line on the IP and the timing cover in order to know how much you are turning the pump. Some people scribe marks every 1mm on the timing cover so that they know exactly how much they are turning the IP. I only put in one mark and eyeballed it.
•*You need the various 15mm wrenches in order to loosen the three 15mm bolts holding the IP to the timing cover. The top bolt is easy (Use the offset box wrench, as is the one on the driver's side. On the passenger side I needed to disconnect the oil line to the turbo and move it out of the way, and also take out the coolant temp sensor (That takes a deep 19mm socket). Once those were out of the way, I used the three wrenches... which ever one would fit and allow me to move the bolt a little bit. Once all three are loose (Don't take them out! Just loosen them!) you can turn the IP. I used a really big channel lock plier to grab the body of the IP and turn it. After moving the IP, be sure to tighten the IP before you start the engine. Yes, you need to warm it up to 180 degrees and then do TDC TIMESET and TDCO LEARN. If it is not at the right value, you need to let the engine cool, loosen the IP, and start over. It took me several hours and a couple of DAYS to do this!
•*I turned my IP towards the driver's side and then did TDC TIMESET and TDCO LEARN. I got an offset value of -2.02. I turned it even further, but still got a -2.02. When this happens, it means you have MOVED TOO FAR and you need to 'start over'. I ended up moving the IP so that that fuel cut-off solenoid was "vertical" with respect to the two valleys of the engine. I then did TDC TIMESET and TDCO LEARN again.
•*This gave me a value of +2.02, so I knew I was too far towards the passenger side. I slowly moved the IP towards the driver's side until I got a -1.94 reading. This took me a few hours, because I had to wait for the engine to cool off between each attempt. When I got to -1.94, I was able to clear the error code 88! Now, although some people like to stick with -1.94, I knew that this is really close to where the diagnostics throw errors, so I moved it just a tad towards the passenger side until I got a -1.5.

After you get where you want to, make sure to clean up the coolant mess if you took out the sensor, and button everything back up!

I hope this is helpful to anyone who runs into the same thing.

-Rob