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Thread: Are these signs of a dead alternator?

  1. #1

    Default Are these signs of a dead alternator?

    ZJ was just making a rapid clicking noise when I turned the key, so dropped in a new battery and it fired up straight away. I put my multimeter across the battery with the engine running and it was reading 12.5V, but the voltmeter in the dash is only just above flatlining. Signs of a dead alternator? Is the in-dash voltmeter driven via the alternator or straight from the battery?

  2. #2
    Back Yard Mechanic DT-RAGZ56's Avatar
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    After its running disconnect your battery, if it dies then your alternator is shot, if it runs rough after disconnect then your alernator is going to die. You can always unbolt and bring to autozone and have them test it for you.
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  3. #3
    Registered ryan86jeep's Avatar
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    there is a differance in what the gauage shows, from what the cig ouput shows, from what the battery shows

    12.5 at idle is LOW
    should be 13.5+

    check all your grounds and connections

    but sounds like your alternator is bad

    i personally would never disconect the battery while the engine is running, so i cannot validate what DT is saying
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  4. #4

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    Quote Originally Posted by DT-RAGZ56 View Post
    After its running disconnect your battery, if it dies then your alternator is shot, if it runs rough after disconnect then your alernator is going to die. You can always unbolt and bring to autozone and have them test it for you.
    Disconnecting the battery while running is a very bad idea with the computers we now have.

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    Quote Originally Posted by georged View Post
    Disconnecting the battery while running is a very bad idea with the computers we now have.
    bump

    Extremely bad idea 10,000%. Murphy will be standing right there if you do to show you just how unlucky you are. Make his day!!!

    He must not like this guy I am glad I don't know people like that.

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    Quote Originally Posted by AVR2 View Post
    ZJ was just making a rapid clicking noise when I turned the key, so dropped in a new battery and it fired up straight away. I put my multimeter across the battery with the engine running and it was reading 12.5V, but the voltmeter in the dash is only just above flatlining. Signs of a dead alternator? Is the in-dash voltmeter driven via the alternator or straight from the battery?
    Well a bit late now but. You should have charged the dead battery and did some checking with the volt meter you clearly have. Portable charge 6-10 Amp left on overnight or most of the day would charge it enough to start. Once started you could do some tests. But the odds are your alternator may be shot and your battery ok. You might have saved some money but with the new battery and a good alternator you'll be in good shape for the winter.

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  7. #7

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    Quote Originally Posted by DT-RAGZ56 View Post
    After its running disconnect your battery,

    Doing that is a TERRIBLE idea. Don't.

    You can even ruin a good alternator and godknows what else doing that.
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  8. #8

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    Thanks guys. I don't live in the USA so I don't have the option of going to an Autozone or anywhere else that will test it for me, it's the dealership or nothing.

    A few more questions:

    Is the alternator relatively easy to replace? I've checked Haynes and it just seems to be bolts, but I guess you really need to have the front of the Jeep up on jackstands to get proper access? It's a 1993 ZJ I6, so the alternator is underneath the AC compressor - can I get it out without having to mess with the compressor?

    If I was concerned about the voltage regulator, are there any checks I can do myself? After swapping in the new battery (from my other Jeep, a 2005 KJ) I took the ZJ for a quick test run, and I had a CEL come up after about 2 minutes of driving. When I got back home, I disconnected the battery ready to put it back into the KJ before thinking "Crap, I should have found out what the code was first", so of course I'll have to do the battery swap again.

    If the voltage regulator is shot, would that automatically throw a code 53 (internal PCM failure detected), or is it less definitive than that?

    And a final question (for now, anyway!) - is ECM just another name for the PCM, or are they two separate modules?
    Last edited by AVR2; 09-22-2011 at 05:06 PM.

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