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Discussion Starter · #1 ·
Greetings fellow Jeep people! 2008 WK Jeep Grand Cherokee - 3.0L Diesel, 205k miles

Last week the alternator went out (probably from oil weeping out of the oil fill cap). I replaced the alternator, which is a decent project in itself, and everything was great until a day later when the battery light came on again. I am somewhat confident the alternator is good, new Duralast, I did some trouble shooting and found this to be the case:
If the battery cables are disconnected and then reconnected, the Jeep starts and the alternator supplies power at 14+ V. Then once I turn off the jeep, leaving the battery cables connected, and turn it on again, the alternator does not supply any power (12 V and dropping). Weird right? I did this several times, disconnect the negative and reconnect it, the alternator works, but turn the jeep off and on again, no charge from the alternator.

I suspect an issue with whatever regulates voltage between the alternator and everything else, but don't understand exactly what that is. Could the electrical connection cable to the alternator be the issue?

Ideas and explanations would be greatly appreciated! Thank you!
 

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Real Jeeps have dents
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Duralast is pretty much the cheapest Chinese junk you can buy. A guy in my local Jeep club says about 10-15% are DOA at the AutoZone store he works at.
 

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Discussion Starter · #3 ·
Well that does it, time to buy a better alternator and do this all over again. I'm just confused why it works after having everything disconnected, and then doesn't.
 

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Real Jeeps have dents
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I have my alternators and starters rebuilt at a local shop that uses German and Japanese parts and performs an extended functional load test to check their work.
 

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Hi.
Fwiw, in the UK we had the 3.0crd for the full production run of the WK, that being 2005-2010. I have never had to change my alternator but have read many threads on both UK and Aussie forums. An Alternator brand that seems to be good quality is Valeo.
 

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I have my alternators and starters rebuilt at a local shop that uses German and Japanese parts and performs an extended functional load test to check their work.
Hi Tim.
Yours is the ideal solution. Have someone skilled in these things recondition your own alternator.

Nearly impossible to find on this side of Atlantic. Most have gone out of business due to cheap, garbage, Chinese junk.

We live in a throw away society. Nobody seems interested in having things fixed anymore, even when the end result would be better.
 

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2007 Jeep WK
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I replaced mine with a rebuilt (local) which was either doa or had a can bus issue. Either way, right out of the box, nothing. Second one worked for 11 months. Got a third on warranty. No compensation for my time. Sent the reman company a nice letter I never got a response to. Hard to not buy Chinese junk when local is just as bad. Should have got a Bosch.
 

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Discussion Starter · #9 ·
Hi Everyone - Replaced the alternator but no luck. The alternator is producing solid power, the issue is something else. My best guess is the voltage regulator, but it isn't clear to me where that is. Is the voltage regulator part of the computer? Is the PCM involved? Thanks for the help!
 

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As I understand it, the "regulator" on the alternator is controlled by the can bus system from the PCM. All the unit on the alternator does is under the control of the PCM, so it's not a stand alone regulator as in the good old days. Check to ensure your new unit has the same number of pins as the old one you took off. Some have one pin, some have two.
 

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Discussion Starter · #11 ·
Thank you, this is what I suspected. Checked and only see one pin and one metal side in the connector to the wire. When functioning 14.5 V is coming out, then after turning off and on a few times there is no charge coming out. Time for a new PCM, shouldn't have ran the Jeep down to such low voltage when the alternator died.
 

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I believe that a certain rpm is required to have it “kick in”. I’m not sure how common pcm failure is. Maybe someone else could chime in.
 
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