Won't run after warm up but fires

From the Chevy Cavalier and Monte Carlo to the Malibu, Lumina and Impala.
Ask our auto mechanics for help to all your Chevrolet car questions now.
Post Reply New Topic
PatrickABCD1234
Posts: 3
Joined: Sun Feb 24, 2019 11:03 am

Won't run after warm up but fires

Unread post by PatrickABCD1234 » Sun Feb 24, 2019 11:33 am

2000 GM 3800 starts normally when cold but sputters and dies after warm up. Will fire but not run again until cool. I've read many posts about this but no solution. I promise to post my solution when I get it figured out, with some help. : )

When warmed up, not starting: Fuel 48psi, spark jumps 35mm gap at end of all plug wires. Cam pulses once per 2 crank revolutions and crank 3/18 pulses are normal 5v also(rotating by hand while probing ICM connector, injectors unplugged). DTC is random misfire. ECT, IAT, TPS, MAF, MAP read normal values. Unplugging MAF makes no change.

When hot it will start and run if reved up while cranking but misfires and will die if rpm gets to low.

From what I have read a bad crank sensor usually causes no spark when it heats up. After the car warms up a bit then died I get pulses from it and spark. Does it seem like the ICM? Or maybe CPU? Thanks!

 

User avatar
TerryAuto
Posts: 317
Joined: Fri Dec 11, 2009 8:48 pm

Re: Won't run after warm up but fires

Unread post by TerryAuto » Sun Feb 24, 2019 3:24 pm

A crank sensor with no signal will cause no spark AND no injector pulse. A bad ICM will only cause no spark. A bad PCM can cause either.
That being said, this does not sound like a crank or cam sensor problem.
Have you checked for a vacuum leak? I have had the Chevy 5.3 V8 intake gaskets cause a similar problem. They seal fine when cold, but when hot they do not seal and cause a vacuum leak- so hard start and it wont idle.

PatrickABCD1234
Posts: 3
Joined: Sun Feb 24, 2019 11:03 am

Re: Won't run after warm up but fires

Unread post by PatrickABCD1234 » Sun Feb 24, 2019 10:06 pm

Thanks for the reply. Yep I did find a small vacuum leak on the backside of the intake plenum and fixed it. However, it seems to be the ICM or a coil that overloaded the ICM. One of the coils let out its smoke today. I removed all the coils and measured the voltage on the ICM coil tabs and got a constant 12v where the smoked coil was. So either the ICM got stuck or was made stuck from a failing coil?

I'll get a new ICM/coil and post if it stays running with the new parts.

PatrickABCD1234
Posts: 3
Joined: Sun Feb 24, 2019 11:03 am

Re: Won't run after warm up but fires

Unread post by PatrickABCD1234 » Mon Feb 25, 2019 9:40 pm

As promised: *drumroll* ICM and one coil was the cause! It seems that the ICM was overheating, due to a coil on its way out, and the heat messed with how the ICM was running.

I bought a used ICM loaded with 3 coils for $20(plus it was mounted on the metal mount!). The seller carries 3800 parts from parted out cars and some new GM parts. He said its not uncommon for a bad coil to take out the ICM. Something to do with the coil rusting and cracking, ...

Post Reply New Topic
  • Similar Topics
    Replies
    Views
    Last post