98 Suburban K2500 problems

[jrsavoie]

I took the Suburban to a friends shop to get tires changed.

I asked him if he would check the timing with his computer while we were at it.

He checked and the timing was good.

He bumped something on his computer and the Suburban started running on 4 cylinders.

He tried relearn. Still the same.

We tried unhooking the batteries for 15 minutes. No change.

I unhooked the PMD and hooked up the spare and the Suburban ran fine. I switched back to the original and it still ran good.

We had the Genesys scanner only code that was in there when it acted up was for cam sensor.

Prior to our adventure there were no lights on.

We cleared the code and the SES light came on sometime later with a code for boost sensor. We cleared it again and after a day or so the SES light came on again with the same code.

I have a boost sensor ordered.

The Suburban is now fish biting some. Mostly at higher speeds.

Is this caused by the boost sensor?

could something else be causing a boost sensor code?

What kind of damage could we have done running the engine on what seemed like one bank of pistons?

Could we have done damage to the PMD?

Any advice would be appreciated.

Thanks
Jeff

 

[NVW]

Check the OS connections, maybe they got partially unplugged. I was also going to mention the CPS but I think you really have to try to reach it, not something that is in your way.

While the hood is up I would check every plug just to be sure.

 

[jrsavoie]

Any answers on my questions though?

 

[buddy]

In what area was something bumped, on the scanner, in the cab, in the engine bay? Were you guessing it was running on 4 cylinders or the scanner showed it?

What is the actual DTC number? Maybe misinterpretting the value as a boost code when its really an OS code.

The 5V reference power to the boost sensor could be shorting, and it might be the same power to other sensors.

 

[jrsavoie]

He was in the cab with the computer.

Going strictly by watching & listening. I thought I was going to lose the motor mounts.

Could you answer all the questions so I can kind of keep track of what I'm trying to figure out?

I don't know the actual number.
Thanks
Jeff

 

[buddy]

If it was an oddball scanner I wouldnt trust it, thats why I think its best to start with known facts than to speculate on what may have happened.

On scanners, there is the ability to turn off injection to single cylinders. This would create an imbalance. If something else is unhealthy could be quite violent until it was stopped commanding on the scanner, or it could have implemented this feature incorrectly. When you intiate the TDCO relearn your OBD2 could do some wierd things too. Do you trust this scanner is accurate in its TDCO procedure, not all of them are made the same or even read the value correctly.

A bad boost sensor can cause you to go into backup fuel mode, aka limp mode. A bad cam sensor (OS) could cause you to go into limp mode and more likely the cause of a fishbite. Air in the fuel lines could most definately cause cam sensor codes and make an engine run like crap, and cause fishbiting.

Better to post the numbers, rather than go by what scanner told you the codes were, because they are often wrong because these diesels have unique ALDL information that isnt used correctly on most readers.

 

[jrsavoie]

Beings ass the scanner is 30 some miles away and I never saw the numbers it'll be pretty hard to post the numbers.

I know nothing about scanners or computers. I am asking for somebody that knows something to educate me.

It was a Genesys scanner. That is all I know about it, Is that good? Bad? Is that what you call an oddball scanner?

If it was an oddball scanner I wouldnt trust it, thats why I think its best to start with known facts than to speculate on what may have happened.

On scanners, there is the ability to turn off injection to single cylinders. This would create an imbalance. If something else is unhealthy could be quite violent until it was stopped commanding on the scanner, or it could have implemented this feature incorrectly. When you intiate the TDCO relearn your OBD2 could do some wierd things too. Do you trust this scanner is accurate in its TDCO procedure, not all of them are made the same or even read the value correctly.

A bad boost sensor can cause you to go into backup fuel mode, aka limp mode. A bad cam sensor (OS) could cause you to go into limp mode and more likely the cause of a fishbite. Air in the fuel lines could most definately cause cam sensor codes and make an engine run like crap, and cause fishbiting.

Better to post the numbers, rather than go by what scanner told you the codes were, because they are often wrong because these diesels have unique ALDL information that isnt used correctly on most readers.

 

[NVW]

If it ran rough by something he did with the scanner I would say he initiated a TDCO learn. Mine sounded like it was going to fall apart.

 

[Acesneights1]

I didn't think that scanner was bi directional with a 6.5TD Unless it's a Tech2 knockoff. This sounds eirly familiar. when Tim(TD) stopped by for a meet and greet along with Matt and Bill(CTChevy427) He threw his Snap On Brick 2500 on my Dually. It did exactly as you describe(except the codes) But the violent shaking like the motor was going to rip loose from the mounts. If the scan tool you are using killed one cyl with a cyl kill it would not run that bad or shake that much. Now we all stoo da round scratching our heads of what the F' just happended. We tried everything and the truck would not run right no matter where Tim put the IP. The happended right after he intiated the 1st relearn IIRC. As a last ditch effort we tried a spare PMD that Tim had with him. Truck started up and ran fine like nothing happended....Well months later I finally had to remove the head off the drivers side due to broken ex bolts and at the same time I removed that PMD(the one causing the shaking) from the IP(where it was mounted) just because it was easy to do so with the head off. I later tried that PMD in My 98 Burb and it works fine...I have no idea why that happended but it sounds like what happended to you and now suspect the Snap ON scanner made something go whacko in the ecm. Don't know, I'm an old school diesel mechanic and hate all this electronic crap. So my poin here is the scan tool may have caused the issue. If you can find out EXACTLY what make and model it is. I'd be curious to know if it's a tech 2 knock off. AFAIK There are two versions of the Tech 2. The Vetronix and the OTC but I am not positive about that.

 

[Big T]

Sounds like your friend should stick to mounting tires.

Yes the boost sensor code could be caused by the boost sensor.

Unlikely your fish biting is being caused by the boost sensor problem, more likely by the PMD.

Extremely unlikely that running on 4 cylinders not under load would damage the engine.

Very probable your tire scan man f'd up the ECM.

Probable that your PMD was already on it's way out.

There, that answers all your questions. So report back what the problem was and stay away from the tire monkey.

 

[jrsavoie]

He has the Genesys scanner if that means anything to anybody
Probable that your PMD was already on it's way out. The PMD was very new but near as I can tell with PMD's that means nothing. As I stated it runs fine on that PMD now and has since I restarted the engine with the spare. - Save for the fish biting

I will try a new PMD if I continue to have the fish bite after the boost sensor is replaced.

Yes the boost sensor code could be caused by the boost sensor.

What I meant was - Could the fishbite be caused by the boost sensor?
There was no SES light or fish bite prior to this whole fiasco

Thanks

 

[Big T]

Extremely unlikely that the fishbite would be caused by the boost sensor. Faulty boost sensor could send it into limp mode to protect engine from over boost. Fishbiting is a momntary fuel delvery issue, not turbo boost. Think electrical portion of fuel delivery when you've got fish bite.

 

[nobby]

I seem to recall reading in the past on various forums, long threads on fishbite troubleshooting that usually wound up being the PMD.

Cheers
Nobby

 

[jrsavoie]

its the OTC Genisys scanner . been out for years. has bi directional controls for many vehicles including 6.5L diesel

I will try the spare new PMD I have in the shop.

Just curious. Do you suppose the violent shaking when it was acting like it was running on 4 cylinders could have messed up the PMD?

I didn't think that scanner was bi directional with a 6.5TD Unless it's a Tech2 knockoff. This sounds eirly familiar. when Tim(TD) stopped by for a meet and greet along with Matt and Bill(CTChevy427) He threw his Snap On Brick 2500 on my Dually. It did exactly as you describe(except the codes) But the violent shaking like the motor was going to rip loose from the mounts. If the scan tool you are using killed one cyl with a cyl kill it would not run that bad or shake that much. Now we all stoo da round scratching our heads of what the F' just happended. We tried everything and the truck would not run right no matter where Tim put the IP. The happended right after he intiated the 1st relearn IIRC. As a last ditch effort we tried a spare PMD that Tim had with him. Truck started up and ran fine like nothing happended....Well months later I finally had to remove the head off the drivers side due to broken ex bolts and at the same time I removed that PMD(the one causing the shaking) from the IP(where it was mounted) just because it was easy to do so with the head off. I later tried that PMD in My 98 Burb and it works fine...I have no idea why that happended but it sounds like what happended to you and now suspect the Snap ON scanner made something go whacko in the ecm. Don't know, I'm an old school diesel mechanic and hate all this electronic crap. So my poin here is the scan tool may have caused the issue. If you can find out EXACTLY what make and model it is. I'd be curious to know if it's a tech 2 knock off. AFAIK There are two versions of the Tech 2. The Vetronix and the OTC but I am not positive about that.

 

[buddy]

I dont think it would have messed up the PMD. Fish biting could be a number of things, air in the fuel line, an IP issue, an OS or CPS problem, a electric short or poor ground.

Purchasing a scanner software can be the most useful tool on these trucks, and usually saves you the cost of the scanner in one repair action being able to diagnose yourself, or timing the vehicle yourself. Just checking the TDCO value doesnt really tell you much, if you ran a relearn and the number was the same as before you did the relearn then you know it was previously timed. Did you get the TDCO value before and after the learn, or did it not actually initiate the learn because of the stumbling? Its difficult to say what might have happened.

 

[Acesneights1]

its the OTC Genisys scanner . been out for years. has bi directional controls for many vehicles including 6.5L diesel

I will try the spare new PMD I have in the shop.

Just curious. Do you suppose the violent shaking when it was acting like it was running on 4 cylinders could have messed up the PMD?

I don't think it messed up the PMD as that PMD later tested good. I think it did something to the ECM that either by changing to a different PMD or the time it took to change to a different PMD seemed to Fix it. It has never done it again. TD, MAtt and Bill all saw it first hand.

 

[jrsavoie]

Please read all the posts thoroughly before posting.

The Suburban was running fine when I took it in for tires.

NO FISH BITE

It was in time when we checked it. It was immediately after checking the timing that something on the scanner was bumped, the Burb Started running like it was on 4 cylinders and the SES light came on.

Getting a scanner don't do shit if you don't know what to do with it. We already done what we set out to do before all the trouble started.

I think he was actually reaching to unplug the damn thing when he did whatever it was he did.

I seriouly doubt it's air in fuel because there waS no PROBLEM BEFORE WE PUT THE SCANNER ON. oF COURSE AFTER THE ENGINE JUMPING ALL OVER THE ENGINE COMPARTMENT it could have pulled a fuel line or ground loose.

The reason we were checking timing is the timing was never checked on any of the engines after the timing chain aND GEARS WERE INSTALLED. We were just checking to see if it was in time or just close. The IP was set by eye.

Does anybody know somebody in Illinois or Indiana that I could trust to take these to. I ain't going through all this again.

If we hadn't checked the timing it would still be fine and the timing was good.

I dont think it would have messed up the PMD. Fish biting could be a number of things, air in the fuel line, an IP issue, an OS or CPS problem, a electric short or poor ground.

Purchasing a scanner software can be the most useful tool on these trucks, and usually saves you the cost of the scanner in one repair action being able to diagnose yourself, or timing the vehicle yourself. Just checking the TDCO value doesnt really tell you much, if you ran a relearn and the number was the same as before you did the relearn then you know it was previously timed. Did you get the TDCO value before and after the learn, or did it not actually initiate the learn because of the stumbling? Its difficult to say what might have happened.

 

[jrsavoie]

On mine I have the fishbite and the recurring SES light since the incident. All was well before hand.

The Suburban was in time when we checked it. We had set the timing by eye when the timing chain and gears were done and we just wanted to see where it was really at. I didn't even have my IP wrenches with me to change it if it was off. We actually expected it to be off a little.

The fishbite and SES light have to be a result of whatever happened. Now I have to get the Suburban fixed. Any advice would be appreciated.

I don't think it messed up the PMD as that PMD later tested good. I think it did something to the ECM that either by changing to a different PMD or the time it took to change to a different PMD seemed to Fix it. It has never done it again. TD, MAtt and Bill all saw it first hand.

 

[buddy]

Only trying to help, and to learn you what youre looking at. You may not be identifying the relevance that others see. Checking the timing is not a simple look at what the scanner says. It may say that the desired timing is this and measured timing is really close, but thats not how these are timed. That value is sort of relative.

The PCM stores the last TOP DEAD CENTER OFFSET (TDCO) value that was set in it. This TDCO value, the tire guy may not even understand. Heres the picture, your TDCO was set before you bought the truck and PCM stored the value. You changed not only the IP position, but also the gears, which all but guarantees the TDCO is NOT going to be the same. However, the PCM is still happy, because it has a stored value that is within its tolerance. Its not the correct value, but it works alright using calculations based on an incorrect assumption that the IP gears are where they were before.

It never intiates its own learn of TDCO. You can initiate the learn with a scanner or the KOKO method. So if you never initiated a TDCO learn and tire guy hit TDCO learn on the scanner, like you needed to do, it could have been so far off of timing that it bucked and kicked because of how far off it was. Base timing could have been too retarded, which is what happens when you initiate TDCO learn, it disables the stepping motor, or steps it as far down as possible to the base timing. The computer may have taken quite a bit of time to learn the differences it was then seeing between the CPS and the OS. And if it was out of tolerance it should have set a DTC, which most scanners wouldnt recognize as a TDCO fault because its unique to this engine.

Now, all that aside anything can be COINCIDENCE and your fish bite may have started that day regardless if you ever visited the tire shop. Most times we start with the last thing touched, and thats it about 80% of the time probably. The violent shaking as you mention can break things loose, ect... Running an IP without proper timing for months and then timing it may have put a groove where it doesnt like to be or who knows.

Just answering your questions doesnt necessarily help diagnose your problem, which is why we must fall back to data we can trust. Unfortunately, we dont know if we can trust the data the scanner provided, although actual DTC values would be reported correctly, not necessarily accurately interpretted by the scanner. The TDCO value may not be translated correctly either. I always advise to check the TDCO value prior to performing a learn, then performing a learn to see the difference.

 

[jrsavoie]

Now that was informative.

Thanks

Looks like I still need to find someplace to take it where somebody know what's what. Does anybody have a clue?

From what I gather the dealerships can't be trusted. I'm about ready to blow the damn things up.

I have 3 here with new timing chain and gears that have never been checked properly. It'd be my guess that the 94 SRW also needs a gears set with 230,000+ miles.

At least the 96 didn't go all crazy when we checked it.