84 Alternator overcharging

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Mar 25, 2016 | 09:50 PM

shawn 84&92

Thread Starter

Burning Brakes

Joined: Sep 2004

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From: Arkansas

84 Alternator overcharging

My 84 alternator was charging up to 16.? volts and the red light was coning on. I took it off this morning and had it rebuilt at a local shop that has been around for years. I put it back on and not is jumps up in the 17's.
What can I check other than the alternator itself? Grounds?

Thanks,
Shawn

Mar 25, 2016 | 10:20 PM

ex-x-fire

Melting Slicks

Joined: Dec 2009

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Might have a bum voltage regulator in it, remove it & have them test it.

Mar 26, 2016 | 02:08 AM

Hot Rod Roy

Safety Car

Joined: Sep 2004

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From: Mission Viejo CA

Is the voltage measured directly on the battery terminals 17 v. too? If the voltage at the battery isn't the same (within about .5 v) as the voltage at the alternator, you have a bad connection on the red + wire from the alternator, or a bad ground connection between the battery and the engine. What is the voltage between the alternator case and the neg battery terminal (engine running)?

Mar 26, 2016 | 02:14 AM

WVZR-1

Team Owner

Joined: Sep 2003

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Quote:

Originally Posted by shawn 84&92

Are you relying on the "in car VM" or are you checking with instruments? If you've questions I'd maybe rely on the shop that did the rebuild.

You've done what I would've done if I had confirmed "with instrument" the problem with an OE/GM alternator. rebuild "local". Was this an OE/GM alternator or a previously rebuilt? GM/OE # still on the case?

You certainly could have potential ground problems. Maybe a Voltage Drop Test:

There's numerous results from a "Voltage Drop Test" using your favorite search engine.

"HRR" - I didn't see your post until after hitting the "SUBMIT"

OP - Do "HRR" suggested checks of B+ from alternator to battery for sure. Maybe just drive to the "local shop", they're likely concerned enough to help.

Last edited by WVZR-1; Mar 26, 2016 at 02:31 AM.

Mar 26, 2016 | 11:44 AM

Danlb

Instructor

Joined: Feb 2015

Posts: 184

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From: Ontario CA

I had the same thing happen to my '84 shortly after I bought it. The alternator had just been replaced by the PO and when the voltage would spike the engine would stumble on acceleration. I pulled the alt and replaced the internal regulator with one I bought at AutoZone along with a new connector. Only took a few minutes and works as advertised now. Cost was less than $30.

Last edited by Danlb; Mar 26, 2016 at 11:47 AM.

Mar 26, 2016 | 07:53 PM

shawn 84&92

Thread Starter

Burning Brakes

Joined: Sep 2004

Posts: 1,130

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From: Arkansas

Thanks guys this gives me some good things to check. I didn't know where to start.
Shawn

Mar 26, 2016 | 08:56 PM

WVZR-1

Team Owner

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Quote:

Originally Posted by shawn 84&92

Thanks guys this gives me some good things to check. I didn't know where to start.
Shawn

If the car runs, drives and is tagged just drive by the shop who did the build for you as I suggested in my first post. If you have the DVM it could be a good drill and experience for tool usage.

Post back for sure!!