Posted by Allen on May 10, 01 at 04:32:48:
Hi! I'm STILL struggling with my '91 Sub V2500's (350, 4L80E, 177K mile body, 79K mile engine, 1K mile trans) intermittant problems, and am just about ready to $uck it up and take it somewhere for diagnosis - or smack it a few times with a big stick.
However, I thought I'd try one more time for some insight and suggestions into an area that I may have overlooked. Here are the facts:
Sometimes when accelerating, it will start to buck and jump (engine RPMs fluctuating), and then correct itself. This appears intermittantly, and I can't determine a set of conditions where it occurs consistant. Idling appears to be okay. The worst part is that it does NOT show any trouble codes.
I was starting to think it happened once it made it to operating temperature, but yesterday morning and this morning, it did it shortly after starting up and driving. So, that shot a temperature-related theory.
The following list shows what parts I've replaced and what I've tried to do. I've owned the truck for five months:
1. Inspected any wiring harness connectors, grounds, ECM connectors etc. that I could find for proper seating and connection. Also inspected for stripped or cracked wires. No visible issues.
2. The catalytic converter has been replaced with a "test pipe" to test if the a plugged converter could be the problem.
3. Checked various lines for vaccuum leaks, but there really aren't very many on the engine (surprisingly!). They mainly appear to be steel lines of some sort and in good shape.
4. All NEW and recently replaced: complete transmission ($$$), coil, cap, rotor, plugs, plug wires, TPS, fuel pump, fuel filter, fuel pump relay, PCV valve.
For the cap and rotor, I used Accel parts. For the fuel pump, I used GM Delco. For the TPS, fuel pump relay, coil, PCV valve and plug wires, I used "Standard" brand.
My thoughts and questions:
1. Could an EGR cause this? Would it set a code?
2. Could an O2 sensor cause this? Would it set a code?
3. Could a coolant temp sensor cause this? Would it set a code?
4. Someone mentioned to me about some wires actually IN the distributor cap (not the spark module). What might they be talking about? Would they go to some pick-up coil or something? How would they cause a problem?
The Sub is very nice overall, and seems to run perfect when it isn't jumping around. This seems very strange to me. I'm used to the all-or-nothing situations with vehicles - when they're messed up, they're messed up consistantly, not this random stuff.
Basically, what else could I do or check out before giving up? Thanks again for all your help!