silverstang84

Hey guys, I'm having a weird problem with my 88 iroc. It has a 350 TPI motor. Sometimes when I start it, the car will run very rough and the check engine light will flicker on and off. Other times I'll start it and it will run fine and then after a while the check engine light will come on and it'll run rough again. I checked for codes but it's just flashing 12 over and over. Is this a ICM problem? What else could this be?

chevypower91

It's odd that you're getting the ses light, but no code. It's possible it could be a faulty ECM or could be a ground issue. Are the ECM and prom original to your car?

silverstang84

Thanks for the reply man. I just bought the car. The previous owner had changed many sensors and relays including the stock computer. So the computer has been changed. It almost seems like there is a loose wire or something. The light flickers on and off and the car will run crappy as soon as the light comes on, then runs normal when the light goes away. The light doesn't stay long enough to throw a code. There's a guy on YouTube that was having a similar problem and it ended up being a ICM.. Does that make sense?

silverstang84

TTT. Anyone else have suggestions?

cheftaylor69

Hello,
I had a situation similar to this, I changed my fuel filter, under car by the back tire area. Cleared up the stutter and SES flashing and gave it nice power again. It is worth a shot, as you pull old one off check the color of the gas as it pours out of filter, you will be able to see if it dark. Also check your injectors as with mine also had some that the ohm was at 6 so changed them all from South Bay Injectors, great people there. Hope this helps, let us know.
Jerry

silverstang84

Thanks for the reply Jerry. I actually just replaced the fuel filter a few weeks ago and the car still has the same problems. It defineltly seems like an electrical issue. I'm thinking it may be relay, mass air, or ecm related. Thanks for the help just the same.

L98_383_Stroker

1. Maybe check the power to the ECM. Make sure you have a good 12 volts. Flex harness gently to see if the 12 volts fluctuates.
2. Might be a PROM error. Pull the PROM. See if the 4 letter code on the PROM is correct for the car. Make sure all pins are not bent and PROM seats fully.
3. You might need to data log your car. This is the only way I know how to see if you have a flaky sensor. Get an ALDL Bluetooth adapter or ALDL USB cable. Data log with one of the tools available.

silverstang84

Ok, I'll start with checking the PROM. Which wire is the main power wire and which is the main ground? I haven't gotten a chance to get under there yet. I'll post results when I can. Thanks for the good info

silverstang84

I'll see if I can post this video

silverstang84

Update: I haven't checked the voltage at the ECM yet but I managed to get a quick video of the car running... This is driving me nuts..

http://youtu.be/UqvsPaNREPU

silverstang84

http://youtu.be/UqvsPaNREPU

L98_383_Stroker

B1, C16 are 12 volts, always on. D1, D2, D3, D12 look to be grounds. A6 looks to be 12 volts via the key.

Did the previous owner give you the old computer?

As far as PROM errors, I've never experienced one personally, but if the code is corrupt, the microprocessor will jump around in the code acting intermittently. Once the microprocessor figures out there is a PROM error, I think it's supposed to go into limp mode. I don't know if it can pop back out of limp mode.

silverstang84

I'll check all this tomorrow/Sunday. Thanks again for he good info.

The previous owner didn't include the original computer.

Did that YouTube link work for you? You may have to copy and paste it. But it give you a good idea how the car is running

silverstang84

Update: even after replacing the ecm the car still has he same problem... Anyone have any ideas?

Jayryan

i have basically the same problem it sounds like with my 89 iroc, was wondering if you ever came to a solution? I've done ecm, all 8 injectors, fuel pump and filter, have good spark, changed o2, tps and iac sensors

silverstang84

the problem has been fixed and it turned out to be a bad prom. The computer was fine. prom was bad. I had Brian (tuned performance) in here make me a new prom and send it out. It's been fine ever since. Hope this helps.

Jayryan

i guess he's changed out the prom already too