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Old 12-31-2013, 01:30 PM
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98 zj check battery, alternator issue

I have a 98 zj 5.2. Lately while driving my volt gauge drops to 9 and check gauges and check battery lights come on. I can shut it off while driving and start it up and it goes back to normal. This is not a constant problem but at random. I clean all connections from alternator to battery and battery terminals. I just put in New battery and still does it. Is my alternator going bad? Voltage regulator? Thanks for the help
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Old 12-31-2013, 02:13 PM
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Re: 98 zj check battery, alternator issue

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Originally Posted by jeepinit1124 View Post
I have a 98 zj 5.2. Lately while driving my volt gauge drops to 9 and check gauges and check battery lights come on. I can shut it off while driving and start it up and it goes back to normal. This is not a constant problem but at random. I clean all connections from alternator to battery and battery terminals. I just put in New battery and still does it. Is my alternator going bad? Voltage regulator? Thanks for the help
You should go get a cheap voltmeter as there are several checks you need to make.

The first one is to make sure the ground from the alternator to the body is nice and clean and good and tight.

Where you bought the battery should have done a charging system check, unless you just bought and installed it.

With the engine just above idle so the alternator should be charging, measure the battery voltage on the connectors, where you should be seeing an absolute minimum of 13.8 volts or you get no charging. Better would be 14.2 to 14.5 or 14.7.
If above 14.7, you risk damaging the battery.

If the voltage is too low at this point, you've either damaged your new battery already or the alternator is due for check and replacement at a decent garage or just swap it yourself.

If you want to check your new battery, you can charge it without the alternator connected, then measure the voltage at the posts, then hook up the terminals and turn on your lights and wait 5 minutes and turn them off. The battery voltage should only drop a couple tenths and should be 13.2 to 13.8 or so volts AFTER putting the lights load on it. If it drops a volt, you may have damaged it already and let your conscience be your guide in getting a warranty replacement.

If you have good voltage as measured at the terminals with the alternator running, then move the probes to the battery posts so you are not touching the terminals, the voltage should be the same as on the terminals within 0.1 volt.

If all still good, measure the voltage from the ground POST to the chassis, where you should never see more than 0.2 volts with the alternator on, lights on, etc. Anything higher indicates a poor ground.

Measuring the positive side is trickier, but you can put one lead on the battery + post, and then move the other to the starter, to the power distribution, etc. to see if you ever see 0.1 volt or more along any path--indicating dirty/poor connect.

To the starter, with it engaged and spinning, you might see up to 0.2 volts along that cable but that would be the max.

Rotsa ruck...
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Old 12-31-2013, 04:59 PM
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Re: 98 zj check battery, alternator issue

Everyone I had a volt meter on me the jeep didn't act up. I just went to check it again and now my alternator is not putting out anything. I checked all grounds and all wires I could. Could the alternator be bad and work sometimes and not others. That seems crazy to me cuz don't they normally just go out and be done?
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Old 01-02-2014, 01:16 PM
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Re: 98 zj check battery, alternator issue

The problem is I don't still have my ZJ FSM, so I don't remember if the voltage regulator is in the PCM or the alternator. Have this dim memory it is NOT in the alternator, so just testing the alternator at an alternator shop wouldn't find problems if PCM.

If you can find a FSM, it would tell you what voltage you should see coming into the control on the alternator if it truly is external--or a jeep shop.
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Old 01-04-2014, 09:42 AM
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Quote:
Originally Posted by lstowell View Post
The problem is I don't still have my ZJ FSM, so I don't remember if the voltage regulator is in the PCM or the alternator. Have this dim memory it is NOT in the alternator, so just testing the alternator at an alternator shop wouldn't find problems if PCM.

If you can find a FSM, it would tell you what voltage you should see coming into the control on the alternator if it truly is external--or a jeep shop.
Free online FSMs, ZJ included, available for use at-

http://www.jeep4x4center.com/knowled...ex.htm#service
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Old 01-04-2014, 07:50 PM
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Re: 98 zj check battery, alternator issue

Voltage regulator is in the PCM. Search for the fender washer temporary fix. If that doesn't work, might be time for a new PCM.
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Old 01-05-2014, 01:24 AM
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Smile Re: 98 zj check battery, alternator issue

I bought a new alternator and installed it and that fixed my problem. (For now) lol. Thanks for the help and giving me things to look at. It's a jeep thing and I still don't understand
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