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My charging system???

D

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NAXJA Forum User
Location
Utah
My voltage gauge goes to 19V and I put a new altornator in abnd still goes to 19V! I had both tested and the battery to and they all work?? SOOOO. Any Ideas??
 
Re: My charhing system???

Well I have lots of ideas, but since you didn't tell us what year I'm not sure what info to give you.

Please read the sticky at the top of the forum.
 
Re: My charhing system???

Have you tested actual voltage, at the battery? Do not trust the dash gauge.

Year is very important info here, since 91 and up have the voltage regulator in the engine computer, and earlier ones have it in the alternator!
 
Re: My charhing system???

Since you have a 1998 the voltage regulator is built into the PCM. Check the wiring and grounds. Also, check for correct voltage, don't rely on the gauge. Shouldn't an auto tech know this stuff?
 
I am having the opposite problem and have narrowed the possibilities down to the PCM. Where is it located in a 95 Cherokee Sport? I am 99.5% sure it is the PCM because I have replaced/tested everything else and the problem always goes away after I "fix" it and then it comes back. The alternator just stops charging. When I remove the battery cables and then put them back on, resetting the computer, the problem goes away and I am charging at 14v again, actually about 13.85v on my digital MM.
 
Multimeter set to volts. Test leads go on opposite ends of the same cable. Headlights on, AC on with blower on high. Check the alternator to battery cable and the battery to block ground. Results should be under .5V, any higher and there is voltage being lost in the cable due to corrosion.

Some here will say an ohm test on the cables is fine but that isn't the case and here's why. Say there's 40 small wires in the cable bundled together and connected at the ends. 39 of them could be corroded with only 1 good- and you'll still get a good ohm reading, but how much current will that cable pass?
 
OK, I will try that. The ground cable is new, replaced it a couple months ago when the problem came back. The positive cable at the battery has new ends on it. I cut the old clamp off and cut back to where I could see clean shiny copper then soldered two new ends on it. I sanded every connection I could find and applied dielectric grease before putting them back together.
 
I did the test as described above and got nothing on the multimeter. I did the test while the problem was occurring and after resetting the computer to remove the issue. I also tested the voltage across the battery in both conditions and verified that the generator was not charging before the reset. I ordered a replacement computer and will post back with the results.
 
JJacobs said:
You got nothing, as in zero? Something wasn't done right, it will always read .1-.2V at least when done correctly.
Click to expand...

Maybe he had the voltmeter on the wrong scale?
 
OK, I managed to find a replacement computer for $55. I replaced the computer and guess what... the problem came back two days later. So, I am back to square one.

When I did the test described earlier, I had the MM set to 20V DC. I put the negative lead on the signal origin and the positive lead on the other end of the wire. I tested from the battery negative to the block ground and to the chassis ground. I tested from the battery positive to the "fuse block". I tested from the generator to the battery positive.
 
I located all grounds under hood and sanded the sheet metal down to bare metal and coated the area with dielectric. Still no love. I have the battery on a trickle charger right now because the Jeep died as my GF pulled into the driveway. I hope we didn't over discharge the battery. There is another thing that may or may not be related. Every once in a while, just after starting, the engine will stumble. We have to gun the engine to get it to run correctly. I found a small vac leak and fixed that but it didn't help any.
 
OK, I am 98% sure that the cause of my problem is the connection between the computer and the alternator. Does anyone have an EVTM for this year Cherokee? I need to know which pin on the computer is the voltage regulator signal and which of the two tabs on the back of the alternator does it go to? What connects to the other tab?
 
Problem has been fixed, I hope. I ended up using one of those pay for an answer sites and they gave me the diagrams and pin outs I needed. I connected two new wires from the alt to the PCM and nothing happened. I checked the voltage on the exciter wire coming from the alt and my meter went to overload. I checked the voltage on the same wire at the PCM and it was at 11.5. I then disconnected the factory wires and just used my new wires. Same problem. I took the alternator out AGAIN and had it tested AGAIN and this time it tested at V just as it was showing in the Jeep. The counter jockey said that it was probably a diode going bad that caused the false positives on previous tests and when I thought I had it "fixed". So $130 later for a reman with lifetime warranty and all is good again. Lets just hope that it doesn't come back.
 
Glad you go it sorted out.

Rant on:

AND ONCE AGAIN THE COUNTER MONKEYS SCREWED UP THE ALTERNATOR TEST ON A NIPPON DENSO EXTERNALLY REGULATED ALTERNATOR.

IF YOU OWN A 91+ XJ DON'T GO TO THE COUNTER MONKEYS AT THE CHAIN PARTS STORES!

Rant off, thank you for the time to vent.
 
Can you elaborate on your rant a little bit? Are you saying that the previous tests of the alternator were false positives that could have been detected in some way? I watched them do it every time and they always did it the same way, even at different stores and chains. If there is some way of telling I would really like to know in case this one starts to do the same thing and tests good. Also, Do you think there is a chance that the it wasn't the alt that was my problem and that the problem killed the alt?
 
I don't know if it was operator error, or machine error, but I have had similar results. I took a alternator to two different Advance Autos and one Autozone. One said it was good, one said it was bad, and one said it worked sometime. Turns out the battery was just dead and the alternator was fine.
 
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