Got this car running a few months ago after throwing fuel pump, fuel filter, pressure regulator, injectors, plugs/wires, idle air control valve (had a high idle, stuck open). Also did the water pump and thermostat as the water pump was leaking. Anyway, it ran fine for a while, was able to drive it to the gas station and such a couple times. Went to start it one day, and it idled like absolute crap, almost to where I had to keep my foot on the gas to keep it alive. Managed to borrow an obd1 scanner from a co-worker and found a plethora of sensor circuit codes and some codes for an internal ecm failure. Replaced the ECM and none of the codes came back and it was running rough still but I didn't have to keep my foot on the gas. Still on the misfire track, I replaced the cheap amazon injectors I'd put in with a decent set of reman OEM ones and replaced the coils as well. With no change. Tested fuel pressure again today and it was within spec (41psi KOEO, and 39psi at idle), the other idea I had was to disconnect the exhaust before the cat to see if a clogged cat was my issue, but there was no change with that either. The exhaust will pop when I rev the engine and it definitely smells like it's running really rich. I'm absolutely stumped on what could be going on here. Watching live data on the scan tool, everything seems like it should be running great. I'm just curious if anyone else has run into something like this or can give me a direction to check that maybe I haven't thought about yet. Thanks!

 

pull plugs and see what they look like. do compression test.

 

Yeah, that's probably gonna be my next step. I've just been putting off because if it is a compression issue, I don't know if I wanna know. lol

 

what kind of blow by you got? could be bad lifter, stuck valve, intake manifold leak, bad head gasket, plug wire grounding out, fouled plug, a code sure would help.

 

There are no codes aside from a pressure control solenoid for the transmission causing hard shifts. Did a compression test today that came out fairly well with everything within spec according to Identifix. I'm also pretty surprised at the condition of the plugs considering they have only a few hours of run time on them. And also captured some live data. I'm familiar with obd2 but some of these obd1 parameters are new to me. Maybe someone more knowledgeable will catch something I'm not here.

 

not sure if 93 and 94 are the same. check tec1 data values in the factory service manual and see if that makes sense.

 

looks like might have a dead cylinder guessing that's number 5

 

Can't seem to find anything about those data values in the manual. And what makes you think cylinder 5 is dead? It had good compression, and the plug doesn't look much different from the rest of them.

 

sorry probly 4, the middle one on the left looks wet. fyi I use ngk plugs not a fan of acdelco plugs.

 

Middle on the left is 3. Top to bottom is 1,3,5. Right stack would be 2,4,6. Cyl 3 did have the lowest compression but still well within spec according to GM service info.