2nd Generation Specific 1986-1992 Discussion

Limp home mode issues, what ive tried and where i am...help? 1991 Na vert

Old 02-18-2016, 10:58 PM
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Exclamation Limp home mode issues, what ive tried and where i am...help? 1991 Na vert

nothing fancy, just a triple black 1991 NA vert. 117k on the clock, all stock. I had an 86GXL in the 90's and nostalgia got me easily.

this car was sold to me because it needed oil control rings (high rpm smoke cloud). So, i've been saving for the rebuild and letting it garage queen for about 5 months now.Every two week so i'd give it a warmup and a lap around the neighborhood and tuck it away.

well, the last times i'd tried that the car went in to limp mode pretty much right after i leave my driveway.

I'm ok with google-fu and was able to track down the CEL check procedure. I plugged a jumper into the single green connector by the battery to negative terminal... (side note, can you leave the jumper like that so you always have the CEL info? harmful, asking for a friend)

My CEL pops up with the rest of the lights, turns off, and then stays on. forever.

@#$%$ i cant use that!!!!

What this leads me to find are a few articles about the OMP/MOP on the S5 and what an ECU killer it is. So i decide to unplug the OMP for now. I'm not sure this is the culprit, just where forum searches all seem to lead.

So, I bought another ECU and unplugged the MOP connectors at the motor with the presumptions that without an MOP it shouldn't be killed and that i will surely get two nice CEL codes for the MOP/OMP.

plugged the 'ne-used' ecu and same conditions appear. CEL, but cant get codes. CEL pops up with the rest of the lights, turns off, and then stays on. forever. yes i copy pasted that, its the same damn thing.

so, since these are old and new is relative i went ahead an picked up another ecu from a more reputable source. Same result.

At this time, i don't see many options aside from doing a total wire trace to figure out if i have continuity or shorting issues, and hoping i'm not just a seriously unlucky ECU buyer (30 day return).

Unless someone out there has some other ideas based on my description or can help me limit the wires i need to trace based on the weird code or something else i've said, or common to the 1991 na/vert. I guess i'll start at the OMP circuit and grounds from the ecu end of the harness?

I saw Fuel pressure and FPR mentioned, but no followup on success...will also see about borrowing a meter to test.

Last edited by juliansr; 02-18-2016 at 11:03 PM.
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Old 03-24-2019, 12:09 PM
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Default Re: Limp home mode issues, what ive tried and where i am...help? 1991 Na vert

Test the green pin and see if you have 12V. If you do then that means it's connected properly to ECU.

Check pin 1D,1F. You might have a problem there. These wires run to a green 6 pin connector at the battery and can also be tested for 12v with green pin disconnected.

EDIT: 1I is the green pin just in case that is your issue.

EDIT: Jesus, this thread is ancient.

Last edited by Rotary Alkymist; 03-24-2019 at 12:13 PM.
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