My WJ 4.0 started stumbling a little like an intermittent misfire. Then the radio started crackling when I accelerated at any throttle setting. Then my voltmeter started surging from 12 volts to 15 volts, then back again. I started getting worried. When I got home, I checked the battery on the posts at rest, 12.64 volts. Started it up, 13.82 volts and steady. Huh.... I let it warm up and took it down the road, 13.75 volts read from meter probes in the power plug. I thought "Well, it's got 218K miles on the original, I probably should change the alternator." I bought a Nippondenso reman and installed it 2 days later. The damn old one stayed rock steady at 13.75 for those 2 days, wouldn't you know it? I still had the misfire and crackling radio however.

I installed the reman and all the problems went away. Weird, huh? I'm thinking bouncing brushes in the old alternator causing variations in the system voltage, like maybe some AC.

I just wanted to pass this on because it was really weird! It didn't set any codes either.

 

Worn brushes or maybe something like the diodes going bad or similar ?