Alt not charging - JeepForum.com

 
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post #1 of 7 Old 04-25-2013, 10:24 AM Thread Starter
jdukie1085
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Alt not charging

I have done lots of research online and have checked everything on my jeep and have come to a stopping point. Just looking for advice on what the next step should be. Im leaning towards having to install an external voltage regulator to solve my issue but not sure.


I have a 99 Jeep Cherokee 4.0.
Im having alternator charging issues. The jeep has New battery, new alternator and i have cleaned all grounds and connectors. I am getting power from the back of the alternator in the gr/or. wire and also power at the gr. wire with the jeep engine on. When I ground the gr. wire I can get the alternator to start charging. i know that the green wire runs directly from the alternator to the PCM.

Is this just the PCM going out and not grounding itself?

Is this just the green wire with a bad ground in the PCM?

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post #2 of 7 Old 04-25-2013, 03:18 PM
CJ7-Tim
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PCM failure is very highly unlike. Poor quality or loose wire connections, and/or old corroded wires will result in poor charging.

Did you test the alternator ? Just because the alternator is new, doesn't mean that it works right.

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post #3 of 7 Old 04-25-2013, 04:19 PM
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Quote:
Originally Posted by CJ7-Tim View Post
PCM failure is very highly unlike. Poor quality or loose wire connections, and/or old corroded wires will result in poor charging. Did you test the alternator ? Just because the alternator is new, doesn't mean that it works right
^THIS^

It's got a lot to do with why I don't deal with chain stores - I used to work for one, and I'm familiar with their parts and testing procedures (both at the factory and in-store.)

Disconnect negative cable from battery.
Check all of your mains connections - clean/reterminate PRN.
Check the wiring on the back of the alternator - clean/reterminate PRN.
Check the studs on the back of the alternator - clean PRN.
Check the mounting for the alternator, as it is also the primary ground for the unit - clean PRN.

Inspect the fusible link wire in the alternator output lead at the PDC - replace PRN (if the insulation is blistered and it feels like there isn't a wire in there - there isn't. Replace with 10AWG fusible link wire, or with a fuse format that gives you a 125-150A rating - I believe your 1999 will have a 117A alternator, OEM. It's a fuse, it's there for a REASON.)

Inspect, clean, reterminate positive mains leads PRN.

I know I said to start with the grounds - that's because, in thirty-odd years of working on cars, the amount of electrical issues I've traced to shonky grounds has run up around 85-90% of them. It's as good a place as any to start, and offers the following advantages:
- It's cheap.
- It's easy.
- It probably wants doing anyhow.
- It will get you in the neighbourhood of other components that may want checking, and therefore get your eye on them.

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post #4 of 7 Old 04-26-2013, 05:48 AM Thread Starter
jdukie1085
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The alternator was tested when i picked it up and also took it back up to get re tested.

If i connect the dark green wire from the alt directly to a ground instead of the pcm the alternator begins charging.

We we disconnect the battery we found a ground fault in the system. So we disconnected the PDC from the battery but the alt and starter were still connected to battery and thats when we see the ground fault. At this point we are assuming its coming after the PDC.

At one point we pulled 3 mini fuses out of the PDC and the ground fault went away. So we tore into the box and put the box back together and could not repeat the ground fault going away. After putting the box back together it was still showing the ground fault and even pulling the fuses didnt change results.

So now we are left wondering...


So left at this point knowing that there has to be a ground fault but not sure where to start looking.
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post #5 of 7 Old 04-26-2013, 11:50 AM Thread Starter
jdukie1085
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Just realized that the small mini fuses we pulled in the PDC are IOD fuses i beleive which would explain the our readings at them. Gonna go check a few more things a bit later and try to diagnose this stupid gremlin.
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post #6 of 7 Old 06-22-2013, 04:27 PM
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post #7 of 7 Old 06-22-2013, 04:38 PM
everhguevara
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i just had the same problem a few days ago, my jeep died on my way back home, replaced alternator, battery and the battery temperature and still the battery wasn't getting any charge, took new alternator off and took it to autozone and tested good, but still decided to buy another one, went to carquest got a different alt and problem solved, pcm should arrive monday, i'll take it back to advance to get a refund.

revolver
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