96 XJ - Wierd charging problem

Here's the full (unabridged) story. My sister's 96 XJ died on her and refused to start a couple of weeks ago. From what she described, it sounded like her battery.

So I ran to Advance & bought an Optima and stuck it in our Liberty, and installed the battery from the Liberty into her XJ. It started right up & seemed fine. She drove it to work & jump started another one of her friends.

Later on that night, she called me and said it again refused to start. I ran out & charged the battery back up. It appeared to start up ok, but the voltage guage was reading around 11 volts (?). When I turned on her headlights, radio, heater, wipers, etc you could watch the voltage guage slowly creep down and then hover around 8 volts or so.

I pulled the battery cable off when the engine was running, and the voltage guage read around 8 volts, yet the engine kept running. The alternator wasn't bad, but seemed kind of weak. I drove it to my house & ripped her alternator out (not fun), brought it to Advance & bought a new (reman) one.

I slapped it in, and put everything back together. It started right up, and was charging around 11 volts again (I wasn't very happy). I turned on the headlights, the blower motor, the wipers, the radio, and whatever else I could turn on electically and watched the voltage gauge slowly creep down again. I could actually watch the headlights get slowly dimmer. During this process, I removed one of the battery connector terminals & noticed that the headlights (as well as everything else illuminated) seemed to flicker?

Since it was in my garage, I put my battery / alt load tester on it. Both tested good when connected together. The battery load tested good by itself, and the alternator gave me a really funny reading testing by itself -- the needle cycled quickly between 8 volts and 18 volts. So.. I guessed it could be the regulator?

After a bit of research, and to my dismay, I found that the regulator is actually part of the computer (Whose retarded idea was that?). I spoke with my Mom's husband (who is actually footing the bill for all of this), and told him what was going on. We decided to take it to a stealership (Glenbrook Dodge to be precise) to have them run a full diag on the computer so we would know for sure.

To spare this thread the details, I'm $85.00 poorer, and they "couldn't reproduce the problem". They said they ran a diagnostics on it, and didn't find a single problem, and they said it was chargine perfectly. When I got there, I walked the technician out to the vehicle and was able to reproduce the problem immediately. His response was "It's probably the PCM.." I decided not to have them touch it anymore and continue troubleshooting this myself.

I priced out PCMs for around $250. Before I dump the cash into one of those, I'd like to be really sure that's what it is. This weekend I'm going to pull the codes myself, & do some other basic maintenance on it. Before I drop the $$ on a new PCM, does anybody else have anything else I could try? Or do you guys think it's the PCM?

Thanks in advance...

[Edit - It has a 4.0L, A/C, and an auto trans]

I'd replace the alternator first.

BTW If the computer is shot it possible you blew it out when you unhooked the cable with the engine running, don't ever do that.

Also possible the PCM died when she jump started her friend's car. Hook it up backwards and you are pretty much welding (don't ask how I know). 96' are in the junkyards now, much cheaper to pull a PCM there.

Good luck

gjxj said:

I'd replace the alternator first.

BTW If the computer is shot it possible you blew it out when you unhooked the cable with the engine running, don't ever do that.

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Alpine said:

I drove it to my house & ripped her alternator out (not fun), brought it to Advance & bought a new (reman) one.

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I hate electrical problems. Have you checked/cleaned your grounds?

98XJSport said:

I hate electrical problems. Have you checked/cleaned your grounds?

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Yep.

make your alternator a one-wire setup with a self-exciting regulator. Less than 10 bucks, and takes the computer out of the charging process

How about your idle? Dropping idle, dropping amps maybe?

toast said:

make your alternator a one-wire setup with a self-exciting regulator. Less than 10 bucks, and takes the computer out of the charging process

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How?

98XJSport said:

How about your idle? Dropping idle, dropping amps maybe?

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It seems to do the same thing at idle or at any rpm..

I've been doing a bit of research on the whole one-wire thing, and it definitely seems like something that's within a reasonable scope to do. Unfortunately, all of the kits I have found seem to be for either a Ford, or a GM-based Delco SI alternator. Does anybody know who carries a one wire conversion kit that would work on a 96 XJ alternator?

Alpine said:

I've been doing a bit of research on the whole one-wire thing, and it definitely seems like something that's within a reasonable scope to do. Unfortunately, all of the kits I have found seem to be for either a Ford, or a GM-based Delco SI alternator. Does anybody know who carries a one wire conversion kit that would work on a 96 XJ alternator?

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My cherokee PCM regulator is failing as well...it definetly gets annoying. My buddy has an electrical repair shop, and he suggested it. I will let you know when I convert mine.

toast said:

My cherokee PCM regulator is failing as well...it definetly gets annoying. My buddy has an electrical repair shop, and he suggested it. I will let you know when I convert mine.

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That sounds good!

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(Whose retarded idea was that?). Volt reg in computer.
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Hay! they saved $4.49 per Jeep doing it that way and do your really think they care you have to pay 100 bucks (used) to replace the voltage regulator/PCM.

Don't pull the cables on any running anything! That test died with the generator.

If you must do it that way. The Alt belt must be tight. The engine must be at 2500 rpm. All normal loads on. NO 1000 watts of rack lights please. Pull neg cable. Blow horn for 2-3 seconds Jeep should remain running and lights should not dim (much). But if your diodes take a dump? Don't come looking.

Unfortunately it does sound like the voltage regulator in the PCM is going bad, or is bad.

I would try one from a junk yard, and / or look on ebay.

I went through over a dozen dodge alternators years ago from jump starting cars. I no longer jump start cars, unless it is with the car turned off (the one with the good battery) and even then I try to avoid that if at all possible. I also never start the car after jump starting the other. Never start a second car while the first is running with the jumper cables still attached. If you do, then plan on regular purchases of alternators/voltage regulators and or PCMs with voltage regulators!

Best thing to do is use a battery charger, or swap out the battery when a battery dies.

Ok, I found some more detailed information on a Dodge forum. Somebody on there said that they got a cheap $10 Dodge voltage regulator, cut the green field wire to the PCM, and spliced the regulator into the blue wire going to the PCM. Nobody mentioned which Dodge voltage regulator though.

Has anybody done something like this yet? If so, what kind of Dodge vehicle should I have the parts counter jockeys hunt a voltager regulator down for?

Thanks in advance..