Been pulling my hair out trying to figure out what's going on with the wife's rig. The whole issue started while we were outta town visiting family. Got to our destination just fine, went to start the Jeep up the next day and got just a click. Thought it was the starter, tapped the solenoid to check, nothing. Jumped it with my father's truck and it started right up, but as soon as we disconnected the jumper cables the Jeep died. Found if I kept giving it some throttle it would stay running, just wouldn't idle. Did some research, found that the alt could be the problem, replaced it, and every thing worked just fine. That was about a month ago.

A few days ago it started doing the same thing, but if I kept my foot on the gas a little bit it would eventually start to idle. Once it was idling I pulled out the multimeter and checked the voltage at the battery (14.4v) and from the the positive post of the alt to the battery ground (also 14.4v). When I got back inside the cab I noticed the "Check Gauges" light was on and the voltage gauge was pegged at +19v. I thought this was odd since I wasn't seeing that high of voltage at the battery or alt.

After doing some reading online about overcharging issues I thought the voltage regulator might be the culprit. I decided to try wiring in an external voltage regulator, can't really afford to source a new ECM and get it flashed (or whatever the proper term is) by a Jeep dealer. I used an 80's regulator part#2VR1, and the corresponding pigtail. I pulled the small plug off the alt, tapped into the Green/Orange wire for the 12v from battery, and then feed the solid Green wire from the alt directly to the field terminal on the regulator.

Here's a diagram I followed...





After this was all finished I jumped the Jeep again and took it on a test drive. Within 2 minutes of driving I got the "Check Gauges" light again, pulled over and popped the hood with the Jeep still idling. Batt read 14.4v and alt+ to batt- also read 14.4v. I did a 15 mile loop to see if the alt was charging the battery. When I got home I shut it down, then immediately tried to restart it. The battery was weak, reading about 10v with the car off and no key in the ignition.


So what the heck is going on here? Why would the gauge say it's over charging when the alt is only pumping out 14v like it's supposed to be doing? It appears that the voltage regulator wasn't the issue, but since it was only $20 in parts I'm not really worried about that. Anyone got some ideas for me, things I could test/check to track down why my battery isn't charging? I thought I would pulled the known good battery out of my car tomorrow and see if I get the same results, but I'm worried about running it down if the car isn't charging and being stuck with 2 vehicles that need a jump.

Thanks in advance for any help ya'll can offer

 

Had a similar issue with my 01 XJ- it sounds completely dumb, but just clean your battery connections. The jeep does not like bad grounds, and my guess is that when it thinks there is a poor connection, it interprets it as a low charge and sends more juice to compensate.
Hit the battery terminals with a wire brush and some battery cleaner. Also check your cable grounds, etc.

 

I my XJ I had bad connection between wire and battery clamp, so I took clamp apart (2 bolts)

 

I suggest you take the battery and alternator to Advance or O'reilly auto parts (or other shop with good test equipment) and have them tested.

Batteries are only good for about three years - how old is yours?

Like others have said, check battery connections, and the grounds on the engine block just below the ignition coil for corrosion.

When you have the battery out, there's a battery sensor at the bottom of the battery tray - examine it. It senses the battery temperature and is used to control battery charging rate. The PCM uses the temp data to vary the battery charging rate. They rarely go bad but if you want to check it, disconnect the sensor connector and, using an Ohmmeter, read from pin to pin in the pigtail harness. At room temp you should read 9K to 11K Ohms.

I replaced mine only because the sping under the disc fell apart and I couldn't find a suitable replacement.

 

Car wouldn't start. (dead or low battery)
Jumper cables to a good battery started it right up. A good indication that everything was ok except the battery.. I think this is where you went wrong.. you should've either put the battery on a proper charger to see if it would hold a charge, or replaced it. Your alternator won't charge up a dead battery. Replace the battery

 

So here's a little update. Borrowed a brand new battery from a friend and dropped it in. Jeep started right up, so I took it for spin around town. Everything seemed to be going ok, voltage gauge was halfway between 14-15v on the dash. Then while sitting at a traffic light the "Check Gauges" light popped on and the voltage gauge was spiked to +19v again. I started heading home and was constantly scanning the gauges, about 2mins after the voltage gauge spiked it dropped down to ≈14.5v. A few mins after that it spikes up to +19v again.

When I got home I pulled the battery to return to my friends, and I got the battery temp sensor out while I was in the area. Inside my house at roughly 70° the ohms resistance was reading about Ω11.8k seems a tad high but it did slowly scale down as I warmed it up with my hand

 

Nonsense, I still have the original batteries in my 1997 Cherokee and 2000 Tundra. Heat is what kills them, not miles or time.

 

Batteries aren't that simple. At any rate, that would only be anywhere near true if you never ran your vehicle. Over time (presumably some of which you drive a certain number of miles), the battery experiences charge/discharge, hot/cold cycles, vibration, and just over time the electrolyte and lead plates degrade. The rate at which these effect an individual battery varies quite widely... but there's no way around it.

 

When you installed the "good" battery did you tighten the terminals or just twist them. If your original died thats why it ran rough. Next the computer wants a fully charged battery so it sends the request to full charge it. Do thats the reason it 19+. Get a good battery,clean terminals and clean the grounds on the body near the battery,the ones below the Coil and where the large ground cable attaches. Get the basics first.
Ron

 

I cleaned the posts and the terminals then tightened the terminals to the battery.

 

Ive been having simulator problems, I bought the same regulator as you, but it was giving fluctuating 15-19v to my jeep.
Charged my battery to 14.18 volts (with disconnected) but as soon as I disconnected, the voltage from altnator was steady 15v. And keeps everything running