I had a lengthy thread about a year ago concerning this problem, but I have never found the solution. The truck has 140,000 km.

Here is the problem: With the engine at full operating temperature, something is commanding the EGR solenoid(s) to open the EGR valve which causes loss of power and plumes of black smoke with any throttle. This problem does not occur until the engine is at full operating temperature. My understanding is the EGR valve should only be open with the engine cold and at idle.

Parts I have replaced to date: EGR valve, both EGR solenoids, vacuum pump, MAP sensor on firewall, coolant temp sensor and (unrelated) OPS and lift pump.

The vacuum is normal at all locations (the solenoids and the wastegate). The EGR solenoids have 12v supply and the ground is controlled by the PCM.

For the past year or so I have had the EGR valve blocked off with a plate and all hoses connected as normal. The truck runs 100% under this condition except the SES light comes on every few days with codes P0400, P0401 (low EGR flow) as to be expected.

A year ago I took it to the dealer who diagnosed it as either the EGR valve or the solenoids. Well as I stated, I replaced both and it didn't help.

Is there some other sensor that could be faulty? Perhaps my PCM is bad? Has anyone had a similar problem and found a solution? It appears to be a simple problem with an elusive solution. Running with the EGR blocked is okay but I would like to solve the problem once and for all.

Thanks for any assistance.

So it works fine for a little while then starts to act up when it warms up?

Yes, it only acts up when it is at full operating temperature (engine hot). It does not act up with the engine cold.

Did you check the vacuum to the baro sensor? it should have 20" at idle. all solenoids should allow vacuum to go through them when plugged in and stop all flow when unplugged.

block the egr valve with a plate as you did [& i did]... remove dash and remove the SES light bulb... problem fixed... did that on mine when i had her... if i still had it, it would be sporting a HD non egr manifold and HD ecm... and perhaps an intercooler... i do miss her... [97 6.5td tahoe...]

the egr system is a piece of dog poop... mickey mouse at its best [as every diesel egr system is]

98 LD can be tricky, with the MAF messing up everything. Thats why your getting codes now, the MAF is telling the computer that your EGR isn't working.
If you know anybody at a dealership the 'best' way would be to reflash to HD and then you won't have any more problems, and even a little more power.

Get a turbo-master and a reflash.

There is vacuum at the baro when the engine is hot, but not when cold. When the engine is cold there doesn't appear to be vacuum past the second (white dot) solenoid.

I would like to go to a HD PCM but I certainly don't know anyone at a dealership. There is a local diesel shop toying with the idea of getting in a newer advanced scan tool capable of reflashing the PCM, I may give them a call. Seems like there are some legal issues there though.

Many legal issues, where are you will determine how big a deal.

Another route is a junkyard L65 PCM will allow you to bypass the EGR stuff for offroad use only, and is reversable in 15 min. or so when you want to go street legal again. Read FAQS on how to build performance for the 6.5 also update your sig per welcome note in sticky thread just below main title heading.

There is vacuum at the baro when the engine is hot, but not when cold. When the engine is cold there doesn't appear to be vacuum past the second (white dot) solenoid. Someone who knows the S engine better should say what's what on the solenoids but I've seen the gm connector splices done wrong by gm and the connection being intermittent on the middle solenoid will keep it from passing vacuum. Plugged in the solenoid passes vacuum, unplugged it doesn't


I would like to go to a HD PCM I would think anyone doing reflashes could flash a HD instead of an S, or you can simply buy an F PCM.

Someone who knows the S engine better should say what's what on the solenoids I would think anyone doing reflashes could flash a HD instead of an S, or you can simply buy an F PCM.Rather than giving incorrect info on a guess of what equipment he is running, might be prudent until he replies back with an updated signature; at least that is why this S engine owner has failed to give a specific recommendation or hazzard a guess, all my expertise is with OBDII wich is markedly different than OBDI S engine.

Here is the problem: With the engine at full operating temperature, something is commanding the EGR solenoid(s) to open the EGR valve which causes loss of power and plumes of black smoke with any throttle.
I had a customer semi recently with almost the identical complaint as you, and he did all the same stuff + he changed his PCM....Still the same problem. I think, its been a while mind you, that it ended up being of all things a faulty PMD that was sending feedback to the ECM when it got hot.

Does my signature show up now? I have a Vin S engine. No mods other than the cat removed. Two IP replaced so far. One at 90,000km second at 120,000km.

Sorry for the lack of information.

This truck isn't red is it?

why do red trucks smoke more:laugh_exp:joke:

I am looking for someone who has had a similar problem and found the solution. If you find humor in my post, I'm glad.

i have a similar problem with a friend's truck that is why i was reading your thread just thought it was funny tdg asked what colour the truck was im guessing he had one at the shop??

Does my signature show up now?
Sorry for the lack of information.
Yup sig info is there now some of this was in your question's title so no big whup on lack of info, but for sake of your next post info will be there and you won't have to repeat and we won't have to try and guess.

Unfortunately you have caught me away from my manuals & my truck for next couple of weeks, I'm working in Mass. & Maine, so I'm pulling this from memory which isn't what it should be sometimes.

98 is OBDII needs a reflash chipping is not an option, until you can afford that, a $75-150 junkyard 96+ F PCM will plug directly into your truck and will allow you to bypass and not throw codes all your EGR stuff. You will have to do a theft deterrent learn though 1st, once learned it won't have to be retaught. When you can afford it, that junkyard PCM becomes the core for your reflash, so you have your stock PCM for street legal driving, & you can offroad drive with the reflash & reconfigure back to stock in short order.

Shim under EGR valve prevents, EGR valve flow meaning anything it can't flow EGR gas as port is blocked off and diphragm can cycle all it wants, so solenoid can act up and not cause performance loss. This can be done with OBDII S or F PCM, EGR position is monitored on S truck via output of firewall baro/EGR sensor, so in a OBDII S shimmed EGR cant throw a code or flow PCM is happy as it is still moving the diaphragm & tracking change to vented vacuum flow for given engine speed but flowing no EGR gas.

But if using F PCM you can plumb vac pump direct to WG solenoid only, from memory solenoids are left to right looking into the engine from drivers side; WG-EGR-EGR vent which is teed to firewall baro/EGR feedback sensor.

With F PCM you can also eliminate the MAF, bad input from MAF real or intermittent wire to it can be a cause your problem as well, as it tells PCM how much air you are flowing, I belched a lot of smoke once when I forgot to reconnect mine following an experiment. 3" PVC in place of MAF sensor will elminate it's honecomb grid restriction.

F PCM will also give a little more fuel than S on will, it will still cut back/regulate via GM's stock programed curves, but for junkyard price that is a good mod for S trucks to bump to F program.

When you disable EGR solenoids & EGR valve for trouble shooting with F PCM or offroad driving only with a F PCM :D mechanically bypass the sensor but leave wires connected to the sensor, it's a stretch but to preclude any possibility of stray trons, or tron crosstalk to your puterized system best IMO to youte wires as planned by GM to maintain any ground loops to prevent EMI/RF problems.

2 IPs replaced seems to be high fail rate lift pump and filter working & clean, what prompted those swaps, lastly get a Heath replacement FSD/remote cooler as soon as you can afford it, and be done with the bad actor PMD on the side of the IP.

Before going beyond the PCM swap to a reflash, or adding/tweaking boost , gages and pipes are your next mods, stock F PCM is a safe mod to do now for a S truck as you haven't done anything except added fuel/boost to stock F engine GM profile.

I think I've located an 'F' PCM from a local wrecker. What is the procedure to swap PCM's?

Do I simply unplug one and plug in the other? Is there some "learning" it needs to do?

Does everything else stay connected as normal? (the solenoids, the MAF, Baro, etc.)

Thanks for the detailed response Turbine Doc.

Make sure the trannies are the same before you buy, then you can initiate TDCO learn manually once you plug it in.

See if they will take it back if it doesn't work or will at least swap for another one I have had 2 instances where theft learn did not work. Check what vehicle it came from the closer to your year and model vehicle the better it will work, also confirm it is OBD II.

I'm fairly confident 4L80 is only auto trans offering for 96+ but check for sure. There is a procedure for setting theft learn I don't have it with me but I think it's in FAQs.

Only thing to installing new PCM is unplug/plug old & new from behind the glove box door, make sure you discharge static by touching bare metal spot on your truck with your hand (dash support bar behonid the glove box lid is a good spot to dissipate static) before making the swap, lifting pos term of both batts is a good idea also.

I've run 96, 97, and 99 F PCMs from burbs & trucks in my 98 without problem, currently running a reflash 96 K2500 VIN PCM, the VINs being different from my truck have not caused me any problem in the 4.5 years I have running F PCMs for offroad. ;) Since you are a K1500 you will need to make sure replacement PCM is also a K series, a C truck PCM may not talk to your 4x4 controls/trans. You may want to access a MT2500 or T2 or another VIN capable reading tool to read the VIN of the PCM you are installing, and get a VIN check on it to see if you can find what kind of a life it led previously

There is a procedure for setting theft learn I don't have it with me but I think it's in FAQs.
Yup it was in FAQs http://dieselplace.com/forum/showthread.php?p=341141#post341141

Lot of good stuff in the FAQs it is why I put it there. Welcome notes are pretty handy also for you newcomers to the site how to search the site.

I just put a lenghty possible cause of this problem in the Black Smoke thread. A faulty or missing EGR doughnut gasket between upper and lower intake manifolds could cause these problems. Couldn't hurt to check it out.

Okay, so now I'm searching for a PCM from a 96+ 6.5L 2500 series with automatic transmission and 4x4.

There is nothing around here (Saskatchewan, Canada).

If anyone knows about one of these in existence at a wrecker, in your garage, etc. I would be willing to buy it from you or get ahold of the wrecker.

My understanding after talking to the dealer is that the PCM's are all the same from 1996-2000 for 1500, 2500 and 3500 6.5L diesels. The difference comes when the PCM is programmed for the particular application.

Thanks for your help.

96-97 and 98-up are different ECMs, LD and HD are different calibrations.

Well I've had no luck finding a PCM from a 2500 series so far.

So, I diconnected the wiring harnesses from the PCM just for fun.

Well, the huge loss of power and black smoke issue is gone!

There is still a very slight hesitation on acceleration and a very minor amount of black smoke which may be a PCM calibration???? that was removed by unplugging the PCM????

Anyway, the EGR system is hooked back up as normal for the past 4 days and everything seems relatively normal.

I am wondering if the PCM didn't like something the techs did at the dealership last time I was there a year ago?

I am still looking for that elusive 2500 HD PCM.

Thanks for everyone's input so far.

www.car-parts.com lets you search local wreckers online. I bought one I found on here.

Thanks to quantum mechanic I've located a few PCM's that may work for the swap on my truck. I am narrowing my search to 1998 - 2000, 6.5L 2500 and 3500 Vin 'F' trucks.

I have a few more questions about compatibility of PCM's.

I am pretty certain the donor PCM will have to have come from a truck with an automatic and with 4x4 like mine.

What I am uncertain about are things like:

1) does it matter if its a 2500 or 3500 series?
2) do gear ratios have to be identical between my '98 K1500 and the donor truck?
3) any other options that would have to be the same to help ensure compatibilty?

I hope someone who has succesfully swapped PCM's can shed some light on this for me, I would greatly appreciate it.

It has to be a 2500 hd with 8 lug wheels no egr. Some LD 2500's are out there with 6 lugs.

and some 1500's are out there with 8 lugs

1500's with 8 lugs are mis badged, they are 2500/3500. GM didn't offer the 8 lug heavy duty half ton w/8 lugs until about 2002.

Okay, so now I'm searching for a PCM from a 96+ 6.5L 2500 series with automatic transmission and 4x4.

There is nothing around here (Saskatchewan, Canada).

If anyone knows about one of these in existence at a wrecker, in your garage, etc. I would be willing to buy it from you or get ahold of the wrecker.

My understanding after talking to the dealer is that the PCM's are all the same from 1996-2000 for 1500, 2500 and 3500 6.5L diesels. The difference comes when the PCM is programmed for the particular application.

Thanks for your help.

BD diesel performance out in bc might have some exchange ecm's.. and they are reprogramed for some more hp too...

I'm not the only one MDThttp://www.dieselplace.com/forum/images/smilies/smile.gif

If its a mis badge the RPO's in the glove box should reveal all, no?

BD diesel performance out in bc might have some exchange ecm's.. and they are reprogramed for some more hp too...

Before buying a BD find out who flashes theirs now, if they are still flashing with a Z industries flash, don't waste your money, I had that one 1st and it isn't worth the money I sent mine back.

Ya I know CR. It's not a misbadge, I have owned it since new (ordered it myself and waited 4 months to get it). If you bought a diesel in a 1500, you essentially get a 2500 despite what the tag sayshttp://www.dieselplace.com/forum/images/smilies/hihi.gif

Ya I know CR. It's not a misbadge, I have owned it since new (ordered it myself and waited 4 months to get it). If you bought a diesel in a 1500, you essentially get a 2500 despite what the tag sayshttp://www.dieselplace.com/forum/images/smilies/hihi.gifMore like a 5/8 ton and the 3/4 hd is the same as a srw 3500.

I ordered a used 2500 PCM from a salvage in Ontario. It matches as close as I can get to my 1500. Hopefully it works. They do have a 90 day warranty.

Make sure you read this thread...
http://dieselplace.com/forum/showthread.php?p=341141#post341141

Already printed that thread. Just waiting for the PCM.

I like that QM a 5/8 ton. I knew I was special:ro)

Well the 2500 HD PCM showed up at the bus depot today. Wasn't expecting it that quick, so great.

I used the Theft Deterrent Learn Procedure and things happened as per the steps. It started up at the end and ran normal. Took it for a quick spin to get the engine hot and everything seems normal.

I'll keep a keen eye on things and let you know if anything else happens in the next few days.