Explosive Situation

My XJ is on it's 3rd battery in 2 years. Problem isn't with the battery though. I think it is getting too much charge?? On vacation 2 years ago, we were on the way back across country and the battery started boiling in Kansas. (You could actually hear it) It was hot to the touch and ready to blow.

It has done that once more since but has only seen around town driving. The battery I have now will get hot and spew a little every so often so I'm sure it's time to replace again.

I know I'm a dope for not trying to solve the problem and for replacing 2 batteries... but it's the kind of thing you put off and forget about. After all it still works. Anyway... any ideas?

Over charging and you need to find out why, alternator probably....cheaper fix than new batteries...

Boiling is a sign of overcharging and that is controlled by the voltage regulator that is part of the alternator. Don't think you can buy just the VR module like you used to be able to on the old chevys but someone on here may have an answer on that.

Yes, bad voltage regulator. I had a 69 camero and the voltage regulator was separate from the alterantor. I changed the alternator and began to cook the acid out of the battery. I took it back to Sears and they told me I had a bad regulator. They also told me to get my warranty battery i'd have to pay them to install a new regulator. Once that was done all was fixed.

Go out and get a new/rebuilt alternator and install it, your problem should be fixed. Alternators today have the regulator built in so you will change regulator & alternator at the same time.

I'm sorry to say that if your XJ is a 93 (as some of your other posts indicate) the voltage regulator is NOT in the alternator, but built into the PCM (engine computer), and thus if that is your problem, the solution is going to be more expensive. You'd better check the voltage at the battery before proceeding too much further, and if it reads high, I'd start shopping for a junkyard PCM (you don't want to know what the dealer wants for it!).

Matthew knows better than me, I was it may of been an 88 XJ like mine. I would not of stuck my foot in my mouth if people posting would say year/engine/mileage info of their XJs.

Yes it is a 93. It reads right at the overcharge line on the gauge actually. I have replaced the computer twice ( one junkyard and one new (OUCH)) for other reasons though and it still overcharges. So there is nothing in the alt. that controls output in this model?

Harvo said:

Yes it is a 93. It reads right at the overcharge line on the gauge actually. I have replaced the computer twice ( one junkyard and one new (OUCH)) for other reasons though and it still overcharges. So there is nothing in the alt. that controls output in this model?

Click to expand...

Actually, reading the 95 FSM (same setup as yours) I note that they suggest either a shorted field control circuit or a bad alternator as the two likely causes of overcharging, so it sounds as if an alternator test is in order first, along with a check of the wiring harness.

I should add that according to the FSM, you should be getting codes for overcharging. The check engine light will go on whenever you're running if these codes are set. Code 41 is open or shorted field control circuit, and 46 is overcharging ("battery voltage sense input above target..."). If neither of these codes is showing up I think you really need to make sure there is actual overcharging. Don't trust the dash gauge.

I know this is an older post.. but I had a plymouth that I had overcharging problems with. I had replaced the PCM without disconnecting the battery... it fried the stock computer (was replacing a Mopar Perf. one).. but the only thing it did was overcharge.. The engine would start and run fine, then almost stall, catch itself and repeat... then I heard the battery boiling... disconnected the battery, swapped the PCM's, and the problem went away..
I have also heard static can do crazy things with the PCM's when handling them..