The battery gauge goes all the way to the right, then comes down, then does it again. Any ideas?

 

Bad connections? dielectric grease worked wonders for me... take your cluster out and put some dielectric grease on every connection then reconnect and see if it worked for you.

 

[QUOTE=Cherry_key;1533385]Bad connections? dielectric grease worked wonders for me... take your cluster out and put some dielectric grease on every connection then reconnect and see if it worked for you.[/QUOTE.

X2

 

If the cluster connections are good, try verifying the voltage at the battery and/or at the alternator with a multimeter.

How long does it peg for and under what circumstances? ie only when driving not idling?

 

had mine do that once, the damn alternator voltage regulator was freaking out and pegged my gauge, fried the battery.

 

In my 99, voltage regulation is done by the PCM rather than being inside the alternator. The PCM grounds the return line from the alternator a certain proportion of the time to set the output voltage, so if that return line (usually green) from the alt to the PCM is grounding somewhere else, it runs at 100%.

I was having intermittent high-voltage and pegging issues for a couple days and rewired this line and it fixed the problem.

 

Thanks for all the info so far. It happens when driving only. I usually turn her off and on again, and it will be OK for a while, then "pegs" again (if that is the right term).

This also used to happen with the oil pressure gauge as well, but not for a long time - now it seems to be the battery gauge. Would that suggest it more likely being the connections in the instrument panel?

 

And I also ment to say that it will last for anywhere from 2min to 10min.

 

If it is happening with your oil gauge too, that would seem to suggest a cluster connection issue. But it could be both. As a starting point I would take apart your dash and unplug, dielectric, replug your cluster connectors. But as jebmccall pointed out, running under high-voltage conditions (if that's actually what's going on) can be very bad for your battery, not to mention just about every sensor on the Jeep

 

You could also try unplugging (and probably wrapping with tape so it doesnt accidentally short to anything) your alternator plug, should have two wires (dark green, dark green / orange). If you can drive around like that and not get any voltage spikes, you might want to try rewiring that green wire to where it connects on the PCM (I can find the pin on my 99 if you want, it should be the same, otherwise consult FSM). Be warned that by running on just battery power you might drain your battery and get stuck somewhere.

--edit-- this may not be necessary to point out, but unplug your battery negative cable and make sure it isn't going to hit the post before you unplug your alternator connector.

 

This may be a little late, and may sound odd, but these things are known for ground issues, I had this same problem on my XJ and it turned out to be a poor ground connection on the firewall directly behind the valve cover (braided wire) I made two corrections to this. 1. add a ground wire directly from battery to front cross member (4-gauge wire) and a second ground on the firewall at the rear of the valve cover (also 4-gauge wire) The entire cab, lights, cluster etc is grounded to that braided cable - to the block. then battery to block by passenger side rear to dipstick tube stud. when the gauge (battery) fluctuates, it's not because of poor voltage, but poor ground. Anyway, that's just my personal experience, and it cleared it up. Hope it helps.

 

My parents 98 did this EXACTLY. It was a bad voltage regulator in the pcm. IT FRIED THE PCM, TCM, AND MOST OTHER ELECTRONICS IN THE JEEP (sensors included). It was costly, and will not be fixed by just replacing the alternator. If your tranny starts to feel sluggish and feels like it will not go no matter how much gas you give it, then your screwed. BUT you may get lucky and its just a connection issue.

Keep this in mind, all the electrinics run on 14.4-12v, so try explaining were the "extra" voltage came from...

 

I was going to go get the battery tested and hopefully that would be good enough. But after reading all of this, it sounds like she has to go in. I wouldn't even know how to test to see if the voltage regulator was bad. Have not had any problems with the transmission, so hopefully the TCM is fine. I will let y'all know what I kind out. Thanks for the help!

 

So I replaced the alternator, and it seems to have done the trick. Thanks guys.