Check Engine and Shift Light but no code? Bad Idle (Page 1/1)
Jeffdylanproctor MAY 19, 07:46 PM
We were working on the AC Relay Plug when suddenly my 86 2.8 v6 5 Speed started running poorly and idling way below 1000 RPMS.

I went around and looked in the car, and the Check Engine Light and Shift Light were stuck on. It would run and drive, but something felt off.

I tried to pull a code, but it doesn't respond to the grounding the terminals.

Any ideas what could cause this?


The backstory:
I've had issues getting my AC working, and I thought my Compressor was bad again but it turned out the relay wasn't clicking. The relay was not bad, and I was using a volt meter to try to figure out the Relay Plug wires (I put a new plug at this location last year). I though I had it figured out, and used some jumpers to get the AC Compressor Clutch to click, and it would. I began thinking that the plug wasn't getting signal from the Climate Control Module, although the radiator fan kicks on when activating one of the three AC choices.

I had a teenager working with me, and somehow when we were testing and jumping the cables in the AC Relay Plug the engine electronic disaster happened.

The car will still start, but it idles very low and the 2 lights wont go off.

Any idea what is going on here? What did we tear up? No fuses are blown. Did we accidently disconnect something with the shift light or some other plug in the engine bay?

[This message has been edited by Jeffdylanproctor (edited 05-19-2024).]

theogre MAY 19, 08:57 PM
Maybe Bad ECM.

AC clutch relay only turn On/Off @ ECM command. All AC switches much Close to tell ECM you want AC.
MIL/CEL & Shift are outputs of ECM.

Car can/will start, maybe even drive, w/ Iffy ECM because some parts of ECM may try to work.

ECM can die from Heat, old age, etc as a lot of parts in a ECM & one bad capacitor etc or crack solder joint can do very weird things.
Iffy Grounds in the engine bay or anywhere else can cause weird problems too so clean/fix that first then coat w/ silicone grease.
https://web.archive.org/web...ierocave/ecmwire.htm

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Jeffdylanproctor MAY 19, 09:10 PM
I was thinking it might be the ECM, but I am hoping not. The ECM isn't all that bad to swap out, but still.
Jeffdylanproctor MAY 20, 08:09 AM
Does anyone have a recommendation of where to buy a decent ECM other than ebay? Or even an upgrade?
Jeffdylanproctor MAY 20, 08:49 AM
It looks like the 2.8 uses a 1227170 ECM, but what about the PROM (Programmable Read Only Memory), can I swap that over from my car? Do the PROM chips get damaged as well?

I love daily driving my Pontiac and want to get it back running. I also think the AC may have failed because of the pressure switch on the accumulator/dryer... I wish I knew what we did when jumping the wires and got the electronics all out of whack.