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Discussion Starter · #1 ·
Hey everyone, first post here but long term reader.

Vehicle info until I can fill out bio:
1997 wrangler sport 4.0l
5 speed

I'm having a major issue with the voltage in my tj, not a clue on what to do from here.

Bit of background story leading up to the issue: I changed out my water pump as it was leaking from the weep hole pretty heavily. After installing the new water pump I started my jeep to get the coolant cycling/burp the system. A few seconds after starting the jeep the dash chimed and the check gauges light came on. I looked and the voltage gauge was pinned past 19 volts so I immediately turned it off. I then searched the forums trying to see what the possible cause could be.

So far I have:
1) Pulled alternator and battery to have tested at 2 different auto parts stores, both tested fine.

2)Cleaned every connection on both the alternator and battery, including grounds to shiney bare metal; No difference.

3)Had the local parts shop do a load test on the electrical system, they told me I had a bad alternator. Purchased and installed a new 136amp alternator out of a dakota as an upgrade to the 90amp I had stock. Still the same exact issue.

4) Put a different, known to work battery in the place of my battery. Same voltage issue.

I've run out of things to check for, it would be awesome if anyone here had some input.

:atomic::atomic:
 

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I just copy and paste this information. Personally I would try to remove the dark green wire from the connector and make a jumper before resorting to cutting it. But cutting it would be quicker. The voltage regulator is in the PCM.

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1. If the system is overcharging, there are two things that could be causing it. One is the Dark Green wire between the Powertrain Control Module (PCM) and the alternator. If this wire grounds out, the system will overcharge. The wire could be eliminated as a possibility by simply cutting it at the PCM and the alternator and running a new wire. Recheck to see if it never overcharges again. If it does not, then leave the wire in place or inspect the harness for damage or a short to ground.

2. If the system still overcharges, then it would be a PCM failure. Before replacing the PCM, verify there is no loss of battery voltage to the PCM on pins 2 and 22 in the black connector. If the PCM loses its battery feed or it is reduced, the PCM will "think" the system voltage is too low and will try to compensate by causing it to overcharge.
 

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1997 PCM is the most failure prone year as it was first year and had some associated issues

Cheapest easiest fix if wiring is OK is swap in an alternator with an internal voltage regulator or connect current alternator to a stand alone voltage regulator

Cheep reliable and no requirement for new PCM

It is such a common failure that there are lots of how to add regulator write ups on the web
 

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Discussion Starter · #4 ·
Thanks for the help! I found the dark green wire and will try Replacing that first to see I it's the issue. If not it looks like I'll be going to a stand alone regulator. Do you have have any suggestions on the regulator so I can do a bit of research on them.
 

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Take a volt meter and while the leads are connected to the battery touch the voltmeter to the battery terminals and then to the lead clamps, make sure the numbers are the same.
 

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I bring it up because recently my voltage gauge on the dash pegged at 19v, I had a brand new battery and my inspection mechanic insisted I needed an alternator... I did what I recommended and the battery read 12.5v while the leads read like 5v. I had to spread the leads apart, clean them like crazy with a wire brush, then clamp them down nice and solid on the posts. Immediate fix. Hopefully your problem is something simple like that
 

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Discussion Starter · #8 ·
I already took the posts off and scrubbed them the best I could but I Def give replacing them a try as they aren't in the best shape.
 

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Discussion Starter · #10 ·
Put on new terminals thinking it could have been that as they were not the nicest, no fix.

Cut and spliced the green wire between the pcm and alternator with a new wire, still 18v at the battery when running.

Going to replace main heavy gauge wires in case somehow theres a short there that I cant see.
 

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Discussion Starter · #11 ·
Just remembered that prior to this happening it stalled a few times coasting in neutral. And would not idle without giving gas to keep the revs up.

Not sure if that is helpful to anyone here?

Ordering the external regulator tonight if no one has any other ideas.
 

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Voltage the PCM sees is referenced to ground so a faulty ground could be as problematic as the other wires you already checked
 

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Discussion Starter · #16 ·
Voltage the PCM sees is referenced to ground so a faulty ground could be as problematic as the other wires you already checked
Would that go for all grounds throughout the jeep? Is there any way to check that besides searching and replacing everything?
 

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Discussion Starter · #18 ·
Ordered that kit, should be here Friday and installed Saturday.

If thats not the issue I will replace all the grounds I can find along with all wires connected directly to alternator/battery.

If that doesn't work I think it'll have to go to a shop :beerdrinking:
 

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Discussion Starter · #19 ·
Well new issue. When I turn the jeep ignition to on I have all dash lights and gauges working properly. 10 seconds after turning the jeep on I the lights and gauges all go out and the check gauges light comes on.

I just did the big 3 and replaced the 17yr old wires as well as 2 extra grounds. Grounds were tested and are good.

I have the external regulator here now but am not sure if its worth installing as it seems more like a short somewhere with the new symptom.

Anyone with any ideas please give me some help.
 
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