Voltage regulator issue solved
I wanted to throw this out there because I saw a lot of threads about voltage issues, battery drains and spikes. My 2003 4.0 WJ was fine, then 2 days ago I started it up went to the store and when I came out she was beyond dead. Not even enough power to honk the horn. I got a jump and had to hold the gas to keep it started. Finally it idles ok so I go home. I'm sitting in the driveway idling it and then the battery gauge starts to go fluctuate going from normal halfway down to 1/4 then up to 3/4. Suddenly I get a loud pop from the speakers and the dash lights start flickering on and off. I shut it off and thinking it was an alternator issue I changed the alternator. After I finished I jumped it again and for about 1 minute it seems ok, then goes haywire again. I hightailed it to my parents house because I have another identical WJ sitting there. I get to my parents and shut it off and again not even enough for the horn to beep. Now I'm thinking voltage regulator in the pcm is fried, but for ****s n giggles I tested the battery with a multimeter. 12.77V but I can't even beep the horn. I ran to the store got a new battery and all is fine now. Just thought that was weird, I've never seen a battery try to take out the entire electrical system before like that, especially when it was fine the day before. Just wanted to share that because I see a lot of similar posts and some people are suggesting that the voltage regulators in the pcm are bad. I just want to strongly urge people to try to swap the battery before condemning the pcm or alternator. Pull a battery out of a friend's car to test it if you don't want to waste money trying things. I assume mine had a bad cell or something.