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Old 07-21-2015, 07:47 PM
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battery or alternator?

Trying to get opinions as to which is the failed part. Alternator check, while running at the terminals was 13.8 v. Battery was 12.8 v while running. Starter was struggling to crank over last few days....any and all comments are appreciated!! 92 yj 4.0

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Old 07-21-2015, 08:28 PM   #2
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Seems like the starter is going bad. What does the battery read when not running?

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Old 07-21-2015, 08:48 PM
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Quote:
Originally Posted by Jeer42 View Post
Seems like the starter is going bad. What does the battery read when not running?
It's not the starter...it cranks fine when battery is charged. 12.8v when its sitting.
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Old 07-21-2015, 09:20 PM   #4
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If your readings are correct both seem a little off. Alternator should be showing 14+, a good battery will be over 13. That said, the starter may be a problem if it's dragging. This would be more noticible on a weak battery. I'd clean all your contacts and grounds on battery and motor/body and check your numbers again.
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Old 07-22-2015, 08:08 PM   #5
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If you have a 1 volt difference between the alternator battery connection and the battery when running you either have a bad ground connection to the battery or the cable has a lot of resistance.

If the battery is 12.8 when running what is it with the engine off, and what is it if it is disconnected?

There is a good chance that your battery is toast and the alternator can not put out enough power to maintain over 14 volts at the alternator when running due to the load.

Take the battery to an auto parts store and have it load tested. Easy to do and free (typically).
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Old 07-22-2015, 09:44 PM   #6
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How old is your battery? I'm guessing you need to replace it soon.
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Old 07-23-2015, 12:53 AM   #7
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Use jumper cables to verify the battery cables are good. I'd lean toward battery.
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Old 07-23-2015, 02:09 PM   #8
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What WICruiser said. Bad connection, bad wire, or bad battery. Most likely reasons
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Old 07-24-2015, 09:07 PM
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Well....I'm finally getting back for those that were curious?? O'Reillys machine said "bad battery" so replaced battery and all is good....for now thanks for the opinions and help. I have another question I will post, ha-ha.

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