Battery over-charging?

[mk333]

My jeep wouldn't start yesterday morning so i boosted it and made my way into work. After 5 minutes the battery gauge went from reading a normal 14.5 to 19, and stayed there til I got to work. I cleaned the connections and terminals and was fine until this morning when it did it again but for only 2 mins or so. Would this be an indication to swap an alternator or battery?  Any help would be great.

[mk333]

Figured it out...regulator in alternator...now I can't find one.   A

[vantagetes]

Most alternators have the regulator built in these days meaning it's time to buy a new alternator. You can either check the voltage with a multimeter to confirm its not the gauge being wrong or take the alternator off and have the parts store check it for free.

[Vinman]

What type of Jeep? I believe the TJ's have the charging regulated by the computer and not the alternator

[vantagetes]

What type of Jeep? I believe the TJ's have the charging regulated by the computer and not the alternator

'91 to '98 I believe.

[mk333]

01 xj,   i believe the regulator is in the alternator... ???hoping it is considering  I think I found the only one to exist. Thanks for the help.

[WagoneerXJ]

my 97 XJ is doing this once in a while too. Every couple months or so. I believe the computer regulates the alternator. Stupid Chrysler!

[vantagetes]

my 97 XJ is doing this once in a while too. Every couple months or so. I believe the computer regulates the alternator. Stupid Chrysler!

Correct the PCM is used as the voltage regulator.

First step is to test the alternator itself. The parts place should be able to confirm if it's PCM regulated or not. I am pretty sure the 2001 XJ goes through the PCM as well.

One thing which may slip through the cracks is check the actual battery itself. A bad cell can cause surface charging and create the high voltage condition. Typically when a battery is damaged like this you won't be able to pull enough power from it to start the engine in the first place but I figured I'd mention it anyway. That being said if you apply too high of a voltage to your battery you're going to damage it in the same way, and possibly blow up your battery which will NOT end well. If you can hear what sounds like water boiling, leave the hood latched and closed, turn off your engine immediately and wait until the sound subsides.

There are ways to wire in external voltage regulators instead of replacing the whole PCM, not sure if the CEL will clear or not by doing this.

[WagoneerXJ]

Ok thanks for the info. I should test the alternator output with a multi-meter while it's running? I know there are fancy testers out there that can tell you right away if there's a bad cell. I do not have one of those, but I have a good working spare Optima I can put in it to see if that helps. I have a spare alternator as well, just in case.

 I had the check gauges light on only when it was showing 19 volts. That went away after a few minutes and it dropped back to 14V. CEL came on the next time I started the Jeep, and only lasted until I shut it off later. Now everything appears fine again.

It did this once a couple months ago, for a few minutes and was fine afterwards.

[Kanueh]

Use the Multi meter with it running, should be about 14 volts.

[mk333]

Thanks for all the info. Wagoneer XJ, my jeep did the same. Well time to test some things out before replacing the regulator I geuss.   Thanks again!!

[yellowjeep101]

I don't feel like reading everything in this. But the first thing I would try is cleaning and replacing the terminals at the battery. If the connection isn't good enough then your jeep can run off the alternator alone and not charge the battery. It would show positive on the gauge and would also cause it not to start. Cheap things first before throwing money at it

[LLYJ]

I would take the time to check your ground circuits - had the same problem with periodic over charging and it wasn't just the terminals - check your wiring and connections from batt to engine, batt to body, etc etc - the fuseable links can be tricky (as in show no resistance on a meter but still problematic under running conditions)

[mk333]

Battery is good (tested today). Took out the battery and cleaned connection points again. Everything is running good now but to mention there was quite a bit of corrosion. I understand this can lead to an over-charge and a coolant flush could correct corrosion? Thanks everyone again !!!