I just had my battery light come on and the volt meter on my 97 expy go to around 18v. It changes with the speed of the motor. Higher RPM higher volts. The trip computer shuts off at all but idle. I put a volt meter on the battery with it running and it is showing 16+ volts at idle. I have never seen an alternator put out more voltage when failing. Anyone want to give me any clues? Battery bad maybe? I'm at a loss other than that.

Thanks

 

Possibly a bad voltage regulator. I would take to alternator (it's very easy to remove) to an autoparts store and have it tested. If it's putting out more than (I think) 14.5 volts then replace it. I don't think you can just replace the voltage regulator on these trucks, as it is part of the alternator.

 

I took out the battery last night and had it tested. 875 Cranking amp battery is putting out 950+ amps. The alternator has fried the battery. I got home and took the alternator out. It is easy I did it a year and a half ago when the factory one finally died at 200,000. I will have it tested today at lunch.

Thanks!

 

Just replace the alternator. The internal voltage regulator failed.

Steve

 

Well just got back from lunch. Alternator is the culprit. Now do I just put it on and run it or will the battery cause this one to fail also? I am thinking I will just be safe and bring the battery in for another test since it is under warranty anyway. I could get a new one free.

 

Alternators are capable of up to 18 volts.
That's why there is a regulator to control the output.
Running an alternator with the regulator bad will cook the battery, over voltage the rest of the truck, blow headlamps etc...... given enough time.
If this just happened, the battery should not be affected to any noteable extent.
Reman... alternators are a gamble anytime from any source.

 

I'd say if the battery is under warranty, just try to get a new one.

Oh and you may know this, but don't use your new alternator to charge your dead battery.

 

If the battery has any age on it I would reccomend that you replace it along with the alternator.I own a starter And Alternator rebuild shop and have seen the problem on several ocassions. chances are you have ruined the battery anyway so why take a chance on getting stranded somewhere with a dead battery.Also the battery could cause your new alternator to fail...

Also In response to the comment Bluegrass Made(Reman...alternators are a gamble anytime from any source}.I dont agree with that I'll put my units up against new ones anytime.The unit is only as good as the person that builds them.I have built units that lasted longer than the OE unit..you simply get what you pay for. dont go to some cut rate auto parts and get a unit and expect it to last as long as a quality built unit..