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1996 Chevrolet S-10 overcharging

Tiny
ATACAPT
  • MEMBER
  • 1996 CHEVROLET S-10
  • V6
  • 190,000 MILES
The alternator appears to be overcharging. With the engine running the alternator will create such a load that the fan belt will start to slip, squeal and get hot. If the small control wire on the side of the alternator is disconnected the alternator quits charging and the slippage and squeal stops. While this is happening the volt meter shows just battery voltage or less. The alternator has been replaced and I understand that the old one did exactly the same thing. Could this be caused by a direct short somewhere in the wiring or could this be a control problem by the VCM? I'm not sure where else to look. Thanks for any advice you give me.

Bill
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Monday, July 20th, 2015 AT 11:58 AM

12 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
What is the battery voltage while this is happening measured with a digital meter?
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Monday, July 20th, 2015 AT 4:24 PM
Tiny
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The battery voltage on a digital meter shows around 11.5 to 11.8. It seems to vary a lot. The volt gauge on the truck shows about the same.
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Tuesday, July 21st, 2015 AT 7:05 AM
Tiny
WRENCHTECH
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So, it's not charging at all then, right?
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Tuesday, July 21st, 2015 AT 11:35 AM
Tiny
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According to the digital meter and the trucks voltmeter no it doesn't. But what baffles me is that when the wire is plugged into the side the engine slows a bit as if a load is being placed on it and the belt begins to squeal. Pulling the plug out stops the squeal immediately. I have never seen anything like this before and I am at a loss as to a cause
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Tuesday, July 21st, 2015 AT 3:07 PM
Tiny
WRENCHTECH
  • MECHANIC
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Try taking your voltage reading on the main terminal of the alternator with the engine running.
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Tuesday, July 21st, 2015 AT 3:39 PM
Tiny
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The voltage at the main terminal is 12.5 volts.
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Wednesday, July 22nd, 2015 AT 1:44 PM
Tiny
WRENCHTECH
  • MECHANIC
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OK, the alternator is just not putting anything out. I would try disconnecting that main wire and see if the alternator still strains.
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Wednesday, July 22nd, 2015 AT 3:21 PM
Tiny
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  • 7 POSTS
I removed both wires from the main terminal on the alternator, clamped them together, started the truck and the alternator does not strain.
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+1
Wednesday, July 22nd, 2015 AT 5:36 PM
Tiny
WRENCHTECH
  • MECHANIC
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Both wires? There should only be one. Where does the second one go?
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Wednesday, July 22nd, 2015 AT 6:01 PM
Tiny
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Not sure where it goes but if the two wires are not connected together the truck goes dark, no power to anything.
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Wednesday, July 22nd, 2015 AT 6:15 PM
Tiny
WRENCHTECH
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There has to be something wrong with one of those 2 circuits. They are both fusible link feeds. It looks like one of them goes to the junction block and one to the starter. The both branch out from there to feed other circuits.
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Wednesday, July 22nd, 2015 AT 6:21 PM
Tiny
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Would a short cause this to happen? I will check both circuits and see what I can find
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Thursday, July 23rd, 2015 AT 5:14 AM

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