Need some HELP with charging system.

Lake919 · Aug 9, 2015

Hey guys so my jeep was idling weird and I checked my voltage and whole running it was down around 13 volts. I pulled the alternator, took it to have it tested and it failed the test three times, so I bought a new one and got home and installed it. It started going up in volts and I thought all was fine, then after 3 minutes the engine was acting weird and I tested it again and the volts are again plummeting. They were at 13.3 and falling with the motor running. Any help will be greatly appreciated. Thanks mike.

Johnnie Walker · Aug 9, 2015

How old is your battery?

Lake919 · Aug 9, 2015

The battery is fairly new. Like maybe 10 months old.

ehall · Aug 9, 2015

Where did you test voltage? On the battery posts or on the terminals or ?

Lake919 · Aug 9, 2015

I tested it from the battery posts, it was running up to 14 volts fine and then all of a sudden it just started dropping. Newish battery, brand new alternator. I am at a loss. It was just dropping fast.

ehall · Aug 9, 2015

Did they test the old alternator in the car or on the bench? Did you keep the test results printout?

Sounds like your alternator is cutting out and car is running off battery power alone

Lake919 · Aug 9, 2015

On the bench, in the little machine they have at autozone. It failed three times. Couldn't get it to the store. Could the brand new alternator be toast? I don't feel like pulling it to have it tested just for it to show good.

ehall · Aug 9, 2015

If you bought the replacement at autozone then there's a non-trivial chance that it is defective out of the box

I would try to do some more tests though. One would be to check voltage at the alternator output while battery voltage is dropping, see if its the same

Tim_MN · Aug 9, 2015

ehall said:
If you bought the replacement at autozone then there's a non-trivial chance that it is defective out of the box

"Lifetime Warranty" parts have the highest rate of failure. Faulty right out of the box is common.

Digger87xj · Aug 9, 2015

The voltage will drop if the battery is fully charged. 13v is nothing to worry about.

Tim_MN · Aug 10, 2015

The dashboard gauge should show 13.8-14.4 volts. If it shows less, I would suspect the alternator, and load test the battery.

Lake919 · Aug 10, 2015

I figured it out. My idle was at 400 rpm. I increased it to 750 and all is great now.

RNMedic · Aug 10, 2015

figure out why your idle was a 400rpm it is controlled by the PCM

Need some HELP with charging system.

Lake919

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Johnnie Walker

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ehall

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Lake919

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ehall

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