96 Wrangler not charging, I'm stumped - JeepForum.com
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post #1 of 14 Old 07-30-2021, 07:31 PM Thread Starter
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96 Wrangler not charging, I'm stumped

Son's 96 Wrangler, 4 cyl, 5 speed manual not charging. Nippondenso alternator. Alternator has been replaced at some point, has a Driveworks sticker on it. I noticed that when I turned the pulley there was no noise at all, no brushes rubbing that I could hear. Took to Advance, guy didn't know how to hook it up. Took it across the street to Autozone, guy seemed to know what he was doing, tested twice, tests good. I cleaned terminals, put back on, no charge. Traced and tested wires from terminal block on alt. to where they go into a big harness on top of the motor, good continuity. Checked voltages on the two field terminals on the terminal block on the alt. When the key is turned on I hear a relay click and get 5 volts on both terminals for a second or so, relay clicks again then it drops to about 1/3 volt for a couple seconds then nothing. Same thing when I start the engine, get voltage for a few seconds, then drops. Jumped the main power wire from the alt. to the battery, no change. Wiggles the wires on the PCM on the firewall, didn't get any response. Got me baffled at this point. Any suggestions? Am I missing something? Should I be getting that same voltage on both terminals?

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post #2 of 14 Old 07-30-2021, 07:40 PM
Boojo35
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I suggest that you find a schematic and diagnostic trouble tree for a 96 Wrangler and download them. Share them with the rest of us and maybe we can help.

We are a great forum but struggle with unicorns.

96 Wranglers just do not exist in most peoples minds.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #3 of 14 Old 07-30-2021, 08:22 PM Thread Starter
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Body tag has Mfg, 5/96 as build date. Oops. I guess this is a 97? Has round headlights. I have a Haynes service manual, not a lot of help in those for sure. I'm looking for a real manual now. Found a receipt for the rebuilt alt. from 2018, one year warranty. Those things sure aren't cheap.
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post #4 of 14 Old 07-30-2021, 08:54 PM
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Tj forum is your friend.... or maybe not.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #5 of 14 Old 07-30-2021, 10:52 PM
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Quote:
Originally Posted by tom3 View Post
Body tag has Mfg, 5/96 as build date. Oops. I guess this is a 97? Has round headlights. I have a Haynes service manual, not a lot of help in those for sure. I'm looking for a real manual now. Found a receipt for the rebuilt alt. from 2018, one year warranty. Those things sure aren't cheap.
You have a 97....there is no 96 Wrangler. Yours is one of the first ever built. The 4cyl was built and sent out first to all the fleet, lease, rental cos, tour cos, etc. The very first ones went to Colorado for Jeep Tours. They were all 4 cyl, manual, no ac, soft tops and steel wheels.

Now to the issue.....Check all the ground wires in the engine bay. On the fenders and firewall. I would unbolt and scuff up then bolt back. Check the wires for issues as well. Make sure the battery cables and ends are all good and connect and stay connected tight. Same with the alternator.

Then I would unbolt and clean, inspect, put back the Crank Position Sensor in the top of the bellhousing. May be failing.

But the ignition can have issues along its path that could cause this by not giving continuous "Run" power after initial "Start" power (in very basic terms).
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post #6 of 14 Old 07-31-2021, 12:15 AM
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I think this is a typical jeep denso alt set up, see attachment.
The field circuit is where I would look.

1st test is with wiring connected one wire of field should be @12v the other wire of field @4 volts lower.
I read that is NOT what you are seeing, next

- remove connectors from alternator,
one field wire (K72 DG/OR) will have battery voltage @12volts ,
the second field wire (K20 DG) should have 0volts*. test and post readings


* may be a slight bias voltage
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #7 of 14 Old 07-31-2021, 05:31 AM Thread Starter
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jtec, thankyou! Now I'm getting somewhere. It's looking like the regulator circuit in the PCM is shot. I'll check the other related items mentioned above but I suspect we'll wind up with an external regulator set up. I was confused by the wiring circuit going to the PCM. Those circuits usually seem to run on 5 volts rather than the full 12 - 14 and I was seeing 4+ or 5 V for a second or two. Thanks again.
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post #8 of 14 Old 07-31-2021, 07:17 AM
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don't jump to conclusions, test and retest before condenmig PCM.

Maybe a wiring issue between PCM and ALT.

Anyway did that diagram above match your set up?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 14 Old 07-31-2021, 07:39 AM Thread Starter
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Yes, your wiring diagram is the exact same as on the Jeep here. I'm going to start checking voltage drops and ground circuits before taking the big hammer to it. Look into the crank sensor too, probably a good PM issue anyway. I know those control modules are designed to be pretty durable but this it pointing to a failure there I'm thinking. At the alternator I think the green/orange wire is the power feed, the darker solid green wire is the pulsed grounding control signal, going to ground that green wire and see if that puts the alternator into full charge too. Everything else on the Jeep is working fine.
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post #10 of 14 Old 07-31-2021, 08:15 AM
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concentrating on alt issue - then will address your CKP questions.

remove the field connections from alt and then check the voltages - as mentioned 1 will have 12v the other 0volts.
knowing that answer will get us to next step.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #11 of 14 Old 07-31-2021, 01:10 PM Thread Starter
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Back in the garage. Took off the connector, terminal (#1)opposite side from ground terminal has about 5 volts for one second when the key is turned on, then drops to 0.35 until key is off. Other terminal (#2)has no voltage. Starting engine the #1 has the 5 V for one second, then goes to 0. Terminal #2 has no voltage. Ran a scan on it, engine cold. trouble codes P0118 coolant temp, P0551 power steering pressure, P0138 O2 sensor bank 1 sensor 2, P1294 target idle speed. Nothing related to this problem??
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post #12 of 14 Old 07-31-2021, 01:38 PM
Jerry Bransford
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If the wiring checks out, contact Mark at www.wranglerfix.com for help which might mean it's fixable with a replacement PCM. The PCM is where your alternator's voltage regulator is. The Wranglerfix guys are gurus with our PCMs, Mark will be able to walk you through and give you an idea if he thinks it is PCM related. Look out, Mark has a wicked sense of humor lol.

When you have a choice, buy American made.
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post #13 of 14 Old 07-31-2021, 02:26 PM
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ok that is wrong, we should see battery voltage @12v on on of the wires.

This is what we will do next, open the loom so you can probe the wires. Blue area.
You want to check wire voltage BEFORE it goes into the plastic molded connector. you want to probe the DG/OR and DG field wires, that molded connector is known to fail its connection.

AT PCM C3 terminal 25 is where the circuit starts, you may want to confirm that PCM is only supplying @5 volts to generator source. see attachment.

If the PCM is only supplying 5v take jerrys advice and contact the supplier he mentioned.

Saturday BBQ and bourbon, and wiring do not mix so thats it until Im sober.
Attached Thumbnails
97 alt field.jpg  
Attached Files
File Type: pdf 1997 TJ GRAY PCM C3.pdf (32.0 KB, 0 views)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #14 of 14 Old 07-31-2021, 08:24 PM Thread Starter
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Took the easy way out, external regulator. Some work to it but working fine. With the dead output from the PCM I'm not seeing any problems just leaving it unhooked. Thanks for all the help, I'm used to older GM stuff and this was sure different.
Attached Thumbnails
jeep voltage.jpg   jeep regulator.jpg  
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