How Do I Know If I Have A Bad ECM, Coil Pack, & Ignition Control Module?


Dec 31, 2005
I am having a problem with diagnosing what is exactly what is going on with my 87 GN. A few days ago, my Scanmaster registered a Code 42, which is EST Failure.

While driving my car, the car will miss or backfire at WOT, so I am thinking that I have a bad coil pack that needs to be replaced.

The car also shut off on me 2 times, both times were when I was stopped at a red light, and when the light turned green, I pressed on the gas pedal and the car just died. I was able to turn the start the car immediately after this happened, and everything was fine thereafter. Again this has occured twice, and I'm not sure what the problem could be as far as this situation. Could this also be a symptom of a bad coil pack, ignition control module, or faulty ecm? I checked the connections to the ecm, and everything seems to be tightly placed with nothing loose.

Could you guys help me out with describing some symptoms that I would be experiencing if my car had a bad ECM, Coil Pack, or a bad Ignition Control Module.

I just don't want to have to spend any money on parts that I don't need to replace at this time.

All help will be greatly appreciated.

I think you have an ignition module problem. That said, I would replace the coil assembly at the same time.Also, the secondary ignition has to be in good shape, or you are liable to repeat the failure. A bad wire will work the coil and module to death trying to fire AT PEAK OUTPUT.
If you had a consistent code 42, I would say follow the appropriate code chart and be done with it, but your primary problem seems to be only there at WOT. Hence,it is difficult to test. You might check coil tower resistance, look for wide variations between the three pairs.Fix this, and I'll bet your stalling issues won't be a further problem.
Good luck, let us know how it is going.
My 86 t-type had some wierd issues like this sometimes... When you said it would die, and fire right back up made me remember all the stuff i did to the car to keep it from doing it again.

First i made sure the battery connections were good, and made sure that the positive battery cable wasnt grounding out with the header under a load.

Next i checked the fuse panel screw in the middle, my car had been apart at one time and the nut on the engine side was really loose, i thought at the time it was not making a great connection.

After i thought the issue went away, i had a crazy power wire under the dash that was chaffing and causing a electricla issue, i was only able to find this out when i was using direct scan...

Last i changed the coil pack out and it seemed to never have this issue again.

I would say the ECM is fine.

Sometimes when the ign modules go out, they melt and it's obvious. Any fellow Buick owners close that could loan you some test parts?