Hi guys, Ive got a bit of a problem that ive been trying to solve for months so hopefully someone can shed some light here. This is a long post so sorry in advance. I have a 1996 Jimmy that i bought with a blown 4.3, I replaced it with an engine out of a 1997 Astro van. Everything went together great and it fired right up, The only problem was it had some major drive ability issues. When you'd start it up cold it started and idled great but put it in gear and start driving and part throttle resulted in misfires and popping from the exhaust and poor power, If i gave it more throttle it would smooth out but it just wasn't making the power it should. If i drove somewhere and shut it off and left it to heat soak for 30 or 40 mins when i started it up and drove away it would run fine and would generaly be good for the rest of the day, but every morning it was the same story all over again bucking and misfires and generally poor running, it never set a single code and looking at the scan data i never saw anything out of whack. I tried changing practically everything by swapping parts from the blown engine back on (coil,ignition module,tps,iac, map sensor,maf sensor, etc) nothing changed the symptoms at all until in frustration i decided to try the PCM that came with the new engine (from an Astro van) this is PCM 16229684 BNHM As soon as that went in the engine ran smooth as silk, hot or cold it runs great no more problems. Just to verify I put the original PCM back in, this was 16244210 BKCX, problem immediately came back, So i thought it must be a bad computer, Got a new used one from Pick N Pull, again a 16244210 BKCX and no joy still the same misfiring and popping, etc. So you may be wondering, why not just run the Astro van PCM since it runs great with that? well I am at the moment but there are a couple of small problems, For one the ABS and Brake lights are on all the time with that PCM (never on with the proper one) and also the AC wont work. Apart from that everything else does work fine, including the cruise control.
So my questions are, does anyone have any idea what is going on here? Why does this engine care if its being ruin by a 96 or 97 PCM? I thought they were virtually the same in those years and they are certainly plug in compatible. Could this have something to do with the crank position sensor relearn business? unfortunately i don't have a scan tool that can carry out that procedure. And what is with the ABS and brake light, and the AC not working? Can somebody point me to PCM pinouts for the 96 and 97 computers so I can see if there is maybe a vss signal on a different pin or something. Again sorry for the long post, this thing has been very perplexing.

 

Your 1996 PCM runs the ABS system, it's the only year GM had the computer run the ABS. That's why you get that problem with the Astro PCM. The boys doing V-8 swaps figured that out real fast, 96=bad year.

Rip out the ABS system and put a later system in, or if you aren't sliding all over the road....ignore it.

There is a TSB that they put the wrong EGR valve on some 96 engines. Buy the EGR block off plate for $10. Use the old computer and see if it is drivable, leave the EGR plugged in but ziptied somewhere's and not actually bolted to the engine. Does this fix the drivability issue? If so keep the old PCM and your happy.

If you want the pinout for the old PCM, search for "95 PCMa" and there's a thread here where they found the late 95 PCM is the same pinout as the horrid 96 PCM. You are lucky you don't have the PCM a few months before the 44210....that one had an internal design failure of insufficient ground to the circuit board and melted due to overheating or loss of transmission function.

Best of luck

 

"Your 1996 PCM runs the ABS system, it's the only year GM had the computer run the ABS." Thanks for that peice of info, that explains why the ABS doesnt work. I did try swapping the EGR valve and it didnt make any difference, I suppose i could try running the original computer with the EGR blocked off and see if that changes anything, Anyone have any clue as to why the AC isnt working?

 

Your PCM also runs the air con. Did the 1997 vehicle have air con?

This link has a guy saying to try shorting the air con low pressure switch to trick the PCM into engaging the air con pump. If that works, it means your pressure is low and the air con needs to be recharged

1996 Chevy S-10 NEW anomoly - Tech Support Forum


Ignore my post on swapping out your ABS module with a later one....appears that would be a wiring nightmare and really would require an entire harness change to a later wiring harness.

 

"Ignore my post on swapping out your ABS module with a later one....appears that would be a wiring nightmare and really would require an entire harness change to a later wiring harness." Yeah I definitely don't wanna go down that road. I dont know if the 97 PCM came from a vehicle that had AC or not, I was wondering if that might be the problem though. ARE the PCM's flashed with different programming based on AC or no AC?
Ideally the best way to fix this is to make it run right with the proper 96 PCM but I cant for the life of me figure out why it runs so badly with that one installed.