Over charging alternator when RPMs are around 3,000 RPMs?

SCXJ

MEMBER
1997 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
400,000 MILES

The charge voltage increases to around 18vdc when the RPMs 3,000. It does not stay at 18v for long, usually drops back to around 14 when RPM is less than 3,000. I verified this 18vdc at the battery terminals. The voltage gauge also shows this high voltage condition.

One more thing is after this over voltage occurs, the transmission won't shift automatically until I turn it off and on again.

Thank you

5 Replies

BRENDON S

MECHANIC
653 POSTS

Good morning, SCXJ,

It is possible the voltage regulator built into the alternator is bad. This part isn't really replaceable so the whole alternator will need to be replaced.

Here is an article with some other tests and a lot of useful information:
https://www.2carpros.com/articles/how-to-check-a-car-alternator

Thank you,
Brendon

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Sunday, April 30th, 2023 AT 5:34 AM

SCXJ

MEMBER
9 POSTS

Brendon,

Thanks for the links and sharing your opinion on the issue. I'll replace the alternator and post the results.

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Sunday, April 30th, 2023 AT 9:41 AM

BRENDON S

MECHANIC
653 POSTS

Hello SCXJ,

You're very welcome. Yes, please let me know how it goes. I will be here.

Thank you,
Brendon

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Sunday, April 30th, 2023 AT 10:16 AM

SCXJ

MEMBER
9 POSTS

Brendon, I just got around to replacing my alternator and you were right, all is well, it's charging my battery at 14v. Thanks for the advice. This is a great service!
SCXJ

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Sunday, June 4th, 2023 AT 8:24 PM

BRENDON S