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91 Grand Am ECM - Need help

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My '91 Grand Am (2.5L TBI, 105k miles) gave up about 2 hours from home. A quick check learned that the fuel injector did not open. With a noid light I confirmed it was not the injector but there was no signal on the wire. Suspicious, I turned the key in the ignition and no check engine light at all. I checked the light and that works. In other words my ECM has problems. Pulled the ECM (that appeared to be a remanufactured one already) out and made sure I had 12 volts on my 2 orange wires. Since that was true I bought a new (remanufactured) ECM. Checked the solenoids for proper resistance, connected the ECM, connected the battery, turned the key and just a crank, still no check engine light coming on. Pushed the plugs, disconnected the battery, pushed some more and at a certain time the ECM would give a continues beep and nothing more.

Is the new ECM also faulty or do I have a wiring problem? I can't pull trouble codes or anything so I don't really know where to go now, any suggestions? I would love to bring the car in to a mechanic, but the car is so far away from everything (before we pushed is it was parked in a no parking zone for a week without any problems) that towing expenses would be more than what the car is worth.

Thanks in advance!

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Reply to
Simon
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Did you switch the PROM chips on the ECMs when you switched them?! Thats the little chip under the cover on one side thats held on with like two little screws. If you didnt do that make sure you do. Being remanufactured you still could have got a bad ECM, they cannot test them at the auto parts store, take it back (I know you paid good for it) and goto a salvage yard and get one

Reply to
A Frazier

At this point, you should have checked for 12 volts with the ignition switch on on the pink/black wires and checked the integrity of the ground wires.

Your condemnation of the ECM was a bit premature.

Reply to
Neil Nelson

Thanks for the reply, my Chilton manual takes quite a few shortcuts when it comes to this part and I never dealt with something similar before. Unfortunately I cannot check the power on the pink-black wires any time soon since I won't be going up to the car this weekend. Just be armed with 'complete' knowledge when I go up there, could you check if the following steps make sense: - I unplug the ECM, connect the battery and turn the car ON. - I ground the Brown/White wire, the check engine light should come on to check the wiring to CEL is ok. - I check on the Pink/Black wire that should have 12V. - I check ground on Black/White, Tan/White, and Tan wires

If this all works as expected, can I assume my ECM is wrong, or are there more steps to take? If I have no 12V on the Pink/Black (I checked all fuses) wire, could this be the ignition and will it work to use power from another wire to at least drive the car home? Is there anyway I could get the car home in 'limp'-mode? That would be very helpful at the moment.

Sorry for the amount of questions, hope you can answer them!

Thanks

Reply to
Simon

The ECM was after core return about $75, not to bad, and worth the risk I thought. The salvage yard is a little cheaper, but why are cars there? Just wanted to play safe. The PROM got switched, I believe if the PROM is wrong the car should still drive but give error messages. I just remembered that the car was getting a horrible gas mileage, overheated quickly (within 5 minutes of stop and go traffic in 80 degree weather) and had intermittently an error code 45 - rich exhaust indicated, checked O2 sensor and that was within specs. Does this help anything?

Reply to
Simon

Chilton books are great for starting a camp fire.

Okay.

Terminal 22 of the black ECM connector.

Terminal 16 of the white ECM connector.

Terminals 12 and 13 of the white ECM connector.

This is the O2 sensor ground, terminal 23 of the black ECM connector. A problem here will not cause a no start bu can cause fuel mixture problems.

Wrong as in wrong part number ECM? A GM dealership should be able to verify the ECM part number for you.

If you have no 12 volts on the pink/black wire, you have an open circuit -somewhere-. Yes, you can jumper to that terminal/circuit with 12 volts from whatever source is handy, won't hurt a thing as long as you're careful. Just remember to disconnect it when finished or you'll have a dead battery the next day.

Not until the ECM powers up, which appears at this point to be the main issue.

I do my best...;-)

The battery and ignition 12 volts can be safely checked with a test light, on a vehicle of this vintage, I am always suspicious of wiring harness degradation... On trick worth using is to substitute a heavier load for your test light, I usually just grab a sealed beam headlamp off the shelf and use it and jumper wires to verify whether the circuit is sound enough to supply enough current to light the sealed beam. DVOMs can trip you up here because it takes very little current to get a 12 volt response on a high impedance DVOM, substituting a sealed beam lamp puts the circuit under more load, any shortfalls in the wiring like chafed wires that are down to one strand will be quickly and easily spotted because the sealed beam will not illuminate.

Reply to
Neil Nelson

Thanks for all the info, due to a sewer emergency in the basement I had no time to look at the car but have good hope I'll find the problem next weekend.

Reply to
Simon

I'm not the all time authority on this, BUT a coworker was showing me his GM ECM connector repair kit the other day. It seems the wiring harnesses are know for loosening up at the pins just enough to cause interesting problems. This may not apply but I thought I'd mention it. GW

Neil Nels> >

Reply to
Geoff Welsh

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