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 Post subject: Did I kill my ecm?
PostPosted: Fri Feb 23, 2018 1:20 pm 
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Joined: Tue Jul 29, 2014 10:36 pm
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Year and Trim: 1991 Bonneville LE
So all was going well with the ol' 1991 bonnie until I had an A/C fuse blow.. I found some frayed wire going to the high pressure switch, repaired it. But then all I had was a 30amp fuse instead of a 25.

Test drive time..all is well! Cool air, runs great, then it starts stuttering and got worse. Finally the engine backfires, wouldn't run.

I swapped the icm, same thing. One day it did start and ran well. Which led me to think it was the icm.

I don't know if I killed the ecm by running a slightly higher ac fuse, or if it randomly failed, or if the crank sensor went out randomly. I did replace the sensor a year ago.

Any help would be appreciated, thanks!

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 Post subject: Re: Did I kill my ecm?
PostPosted: Fri Feb 23, 2018 8:26 pm 
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Joined: Sun Aug 22, 2010 11:11 pm
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Location: Ontario, Canada
Year and Trim: 2000 Bonniville SSEi L67
I dont see how the pcm can be suspect. so the car cranks but not start?

then go through the diagnostics here - you will test the pcm in one of the steps..........http://easyautodiagnostics.com/gm/3.8L/ ... RhcnQiXQ==

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 Post subject: Re: Did I kill my ecm?
PostPosted: Fri Feb 23, 2018 8:36 pm 
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Joined: Tue Jul 29, 2014 10:36 pm
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Year and Trim: 1991 Bonneville LE
Thank you very much. The car does kind of run, it's running like an old car with the distributor on backwards. Except that one day it ran well for a few minutes and then I shut it off. I thought the ignition control module was suspect because they can heat up and send spark to the wrong cylinder. But I've swapped coils and module and the same thing happened cold.

It is baffling as to how I could have messed up the ecm by installing a slightly higher amp fuse for the a/c. This may be a case of two unrelated problems occurring.

I will go through the procedure and see what I can come up with. Thanks for posting it.

And if anyone thinks of anything else feel free to chime in.

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 Post subject: Re: Did I kill my ecm?
PostPosted: Sat Feb 24, 2018 10:25 am 
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Year and Trim: 1991 Bonneville LE
Update: Once again I started the car and it ran fine for about 10 seconds then severe backfiring and the engine barely ran. Could a bad ecm work temporarily, could a crank sensor work temporarily?

I worry that if I perform the test it might show the crank sensor as being good when it isn't.

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 Post subject: Re: Did I kill my ecm?
PostPosted: Sat Feb 24, 2018 12:54 pm 
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Location: Ontario, Canada
Year and Trim: 2000 Bonniville SSEi L67
please go through the crank no start diagnostics to test the components.

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poverty forces one to do unorthodox things

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past rides:
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1987 Grand Am


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 Post subject: Re: Did I kill my ecm?
PostPosted: Sat Feb 24, 2018 12:55 pm 
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Year and Trim: 1991 Bonneville LE
Another update. It appears that the crank sensor or harmonic balancer are having issues. I noticed a frayed wire going to the sensor which I repaired. It didn't fix the problem, but I did notice that when the car is running there is noise coming from behind the crank pulley. This is good to know, but at the same time it is frustrating as I've replaced the crank sensor and harmonic balancer a year or closer to two years ago.

I suppose this thread has run it's course. I'll have to pull the crank pulley and see whats going on. Thanks all for your thoughts and responses.

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 Post subject: Re: Did I kill my ecm?
PostPosted: Sat Feb 24, 2018 1:37 pm 
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96 SSEi

Thanks for the help. I think I would have done the test if I didn't hear that noise behind the pulley.

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 Post subject: Re: Did I kill my ecm?
PostPosted: Sat Feb 24, 2018 4:10 pm 
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Joined: Sun Aug 22, 2010 11:11 pm
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Year and Trim: 2000 Bonniville SSEi L67
n.p. but I doubt mechanical noise is related to your issue unless the ck sensor is not secure.

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 Post subject: Re: Did I kill my ecm?
PostPosted: Mon Feb 26, 2018 8:20 am 
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Year and Trim: 2003 SSEi
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Noise behind balancer could be timing chain, although not common on 3.8. I've seen where the chain is so loose where the engine will go in and out of time as it cranks. Sometimes it will run, sometimes it won't. Also wouldn't take long for me to be suspicious of the ECM on late 80s, early 90s GM stuff. Lots of cracked circuit boards back then. The test was to remove the ECM from the bracket, and tap on the case. If you can get it to run long enough, you will hear the engine stumble while rapping on it.


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