88 2.5L running issue :( please help (Page 3/5) gtxbullet DEC 03, 07:40 PM I replaced the entire Igniton set up on my 88 coupe with a known good one. and it actually ran worse...lol I'm figuring out exactly what I originally thought is the answer...the harness is bad. because it's the only part I haven't swapped off yet... I'd love for someone to come her and help me figure it out before I replace the harness... though because it's a 2.5L the harness is so simple to swap out, it's still money I'd like not to spend gtxbullet DEC 19, 12:28 AM ok. Ive kinda given up... I've spent hours almost every day trying to figure this out... I've swapped every part off and nothing changed. only thing I havent done now is put a whole different engine harness. but this is because the original harness has no problems and no damage... all I want for christmas is my 88 to run good again and not stall all the time. pdemondo DEC 19, 11:49 AM I had random stalling on a 3500 (swapped in place of a 3400) in my Chevy Venture. It turned out being a few semi-shorted wires going to the coil pack. If you have not done so, I would suggest taking out the entire harness and checking the entire thing. Do continuity checks and visual inspection. Faulty wiring on the harness that could have taken out some sensors so, depending of what is bad, you may have to replace a few more parts. I hope you find it, I know how impossible these odd failures are to pinpoint. Good luck. gtxbullet DEC 19, 05:37 PM that's kind of what I'm figuring even though I know all my connections are good I can't see all wires because of the factory loom. quote Originally posted by pdemondo: I had random stalling on a 3500 (swapped in place of a 3400) in my Chevy Venture. It turned out being a few semi-shorted wires going to the coil pack. If you have not done so, I would suggest taking out the entire harness and checking the entire thing. Do continuity checks and visual inspection. Faulty wiring on the harness that could have taken out some sensors so, depending of what is bad, you may have to replace a few more parts. I hope you find it, I know how impossible these odd failures are to pinpoint. Good luck. fieroguru DEC 22, 12:10 PM Do you have a spare instrument cluster? The stalling when pushing in the clutch might be VSS related. Sure your speedo is working so the VSS is fine, but the speedo sends a buffered signal to the ecm. When the ECM sees the fiero in motion from the buffered signal, it raises the idle RPM set point to avoid the common issue of off throttle stalling when the clutch is pressed. I suspect the ecm might not be seeing this buffered signal for some reason (bad buffer board or wire). Might be worth swapping instrument clusters (or just the speedo) to check. Have you tried unplugging the A/C relay and driving the car with the defrost on? With defrost or AC on, the ecm will bump the idle RPM to overcome the pumping loss of the a/c compressor. By unplugging the AC relay, the compressor clutch will not engage and the pump will remain off, but the ecm will raise the idle RPM... which might be enough to stop the stalling condition temporarily and allow you to drive it more. gtxbullet DEC 22, 02:23 PM quote Originally posted by fieroguru: Do you have a spare instrument cluster? The stalling when pushing in the clutch might be VSS related. Sure your speedo is working so the VSS is fine, but the speedo sends a buffered signal to the ecm. When the ECM sees the fiero in motion from the buffered signal, it raises the idle RPM set point to avoid the common issue of off throttle stalling when the clutch is pressed. I suspect the ecm might not be seeing this buffered signal for some reason (bad buffer board or wire). Might be worth swapping instrument clusters (or just the speedo) to check. Have you tried unplugging the A/C relay and driving the car with the defrost on? With defrost or AC on, the ecm will bump the idle RPM to overcome the pumping loss of the a/c compressor. By unplugging the AC relay, the compressor clutch will not engage and the pump will remain off, but the ecm will raise the idle RPM... which might be enough to stop the stalling condition temporarily and allow you to drive it more. my 88 coupe has Zero options. as for switching the gauge cluster out I've already tried it... but just for the heck of it I'll try it again hey make sure the connections are all good gtxbullet DEC 26, 06:24 PM codes - 24, 34, 42 24 - vss signal not reaching the computer 34 - map sensor 42 - ignition related ( ignition module) all gauges function properly. ignition module was replaced a little over year ago. the spark plugs and wires are brand new. I have already tried swapping computers, coil packs, ignition modules, the heat sink backing plate on the ignition module, gauge cluster, idle air control valve, through trying different ones of all those parts nothing changed. I tried rerouting the spark plug wires nothing changed. I have checked all electrical connections as well as the harness...no damage found anywhere. fieroguru DEC 26, 07:06 PM You are going to have to stop throwing parts/spares at this issue and start doing some true diagnostic checks if you want to solve this issue. The good thing about it setting codes is it gives you a few places to start. If you don't have an 88 service manual, get one. It has troubleshooting flow charts for every diagnostic code and will walk you through the troubleshooting process. This may or may not be the method in the service manual, but this is how I check for MAP sensor issues: Turn the key on and check for 5V at Pin C (grey wire). This 5V wire is shared with the TPS as well, so if you don't get the full 5V, unplug the TPS sensor and check it again. If the reading changes, there might actually be something wrong with the TPS sensor that is pulling down 5V ref signal that both sensors use. Then check the ground wire Pin A (black wire) and measure the ohms between it and the engine block and between it and the negative on the battery... if either of these measurements isn't very close to zero, then you have some poor ground connections. Last check the map signal wire pin B (light green). It helps to have a mighty vac or some external means to apply a varying amount of vacuum to the sensor, as you do this you want to see a gradual change in the sensor reading and no dead spots. You can do the same multimeter checks on the ground and power wires on the coil pack to rule out a basic power/ground issue... 86soon3.4 DEC 26, 08:20 PM quote Originally posted by fieroguru: You are going to have to stop throwing parts/spares at this issue and start doing some true diagnostic checks if you want to solve this issue. The good thing about it setting codes is it gives you a few places to start. If you don't have an 88 service manual, get one. It has troubleshooting flow charts for every diagnostic code and will walk you through the troubleshooting process. This may or may not be the method in the service manual, but this is how I check for MAP sensor issues: Turn the key on and check for 5V at Pin C (grey wire). This 5V wire is shared with the TPS as well, so if you don't get the full 5V, unplug the TPS sensor and check it again. If the reading changes, there might actually be something wrong with the TPS sensor that is pulling down 5V ref signal that both sensors use. Then check the ground wire Pin A (black wire) and measure the ohms between it and the engine block and between it and the negative on the battery... if either of these measurements isn't very close to zero, then you have some poor ground connections. Last check the map signal wire pin B (light green). It helps to have a mighty vac or some external means to apply a varying amount of vacuum to the sensor, as you do this you want to see a gradual change in the sensor reading and no dead spots. You can do the same multimeter checks on the ground and power wires on the coil pack to rule out a basic power/ground issue... What he said.... Steve gtxbullet DEC 27, 06:45 PM I'm done swapping parts as I have tried all my spares (clusters, sensors, etc, etc) I checked the MAP sensor and it reads exactly what it should. I'm going to try testing it while driving. still have codes 24 (VSS), 34 (MAP), 42 (ICM)