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Alternator smoking and flames

Tiny
CHARLES GROUPP
  • MEMBER
  • 2005 JEEP GRAND CHEROKEE
  • 3.7L
  • 6 CYL
  • 100,000 MILES
Bought a used car engine runs great drives smooth. Overheated on the way home had a bad cooling fan relay. But then the alternator started smoking and flames came out. Replaced it but checked for shorted or grounded wires first. Checked battery it will take a charge and it holds at 14v for days. Car starts but before it can heat up the alternator again smoked and flamed out again. What could the problem? The pcm contains the voltage regulator. Suspect the PCM is causing the regulator to run the alternator full bore. Any other thoughts?
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Wednesday, July 28th, 2021 AT 2:42 PM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

Either the PCM is bad or you have a short allowing the alternator to run full power at all times. And yes, the voltage is regulated via the PCM.

I attached the wiring schematic below for the charging system. Check the wiring between the alt, pcm, and battery to make sure nothing is shorted. Also, make sure the connector at the alt isn't damaged as well as at the PCM. Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

You indicated the battery is at 14v all the time. That shouldn't be. With the engine off, it should be around 12v. With the engine running and a properly working alternator/regulator, it should be around 14v. Let me know about that.

It sounds like you have the potential for a fire, so be careful.

Let me know what you find.

Joe

See pic below.

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Wednesday, July 28th, 2021 AT 10:30 PM

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