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Old 06-28-2012, 08:52 AM   #1
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Voltage/alt issues

How do I test the alternator to make sure it's working properly

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Old 06-28-2012, 09:34 AM   #2
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Check your battery voltage with engine off/on. Should be 1-2 volts more with engine running(approx.13.5-14.5v). Another crude way of checking it would be disconnect the battery negative cable with engine running. Bad alternator would kill the engine.

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Old 06-28-2012, 09:38 AM   #3
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Old 06-28-2012, 09:51 AM   #4
Knows a couple things...

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Quote:
Originally Posted by Wattapunk View Post
Another crude way of checking it would be disconnect the battery negative cable with engine running. Bad alternator would kill the engine.
That isn't true with the TJ's alternator which requires 12 volts from the battery for it to work. Disconnecting the battery will always kill the engine on most modern engines, not many vehicles still use the type of alternator that can run without a battery. GM is one except and there are others but...

In fact, if you have a completely dead battery and jump start any modern Jeep's engine, the engine will die again after you disconnect the jump start battery. Same thing is true with my daily-driver Toyota whose battery gives me fits.
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Old 06-28-2012, 09:59 AM   #5
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Didn't know that. Thanks for the info.
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Old 06-28-2012, 11:04 AM   #6
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Thanks for ALL the great information -you guys rock! (no pun intended - ok maybe I did)

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