Yesterday I got in the XJ, started it up and went down the street and everything was fine. I stopped at the corner to wait for traffic to clear so I could turn left. When I hit the gas to go, it started to miss and was running real sluggish. I looked down at the dash and noticed that my voltage guage had not moved. It was still at zero. I also had no turn signals. I managed to limp home and checked it with my multi-meter and had no output from the alternator. I ripped it out and went over to Kragen(the closest place) and bought a new one, took it home and slapped it in. When I fired up the the motor and drove it around the guage was back up to just under 14 volts. That was about 6:00 pm. Today when I went to go to a local concert, I started it up and left and the guage only went up to about 12 volts. When I got home I check it with the multi-meter, it was only reading 11.34 volts. Me thinks me got a bad replacement. What do you guys think?

Might also be the battery. When bad, a battery can actually cause resistance to flow. I'd load test the battery.

Also, check your positive battery cable for corrosion - that can cause similar problems.

If they're good, then I'd agree with your diagnosis of a bad alternator.

The cables and the battery are about a year old. I cleaned them about 2months ago andre cleaned them before I put it back together after installing the alternator. (I removed it from above not below, so I took the battery and the battery tray completely out). Today when I left for work the guage only went up to about 12 volts again then after I went about 4 blocks it went down to zero and started running like crap again! I took the alternator back out and I'm going to take it back tomorrow and have it bench tested.

If the alternator tests ok, I'd suspect a bad voltage regulator or something that manages the current. (Can you tell I'm not the electronics guy!)

If the alternator tests ok, I'd suspect a bad voltage regulator or something that manages the current. (Can you tell I'm not the electronics guy!)

Actually the voltage regulator would be a good guess, but the alternator has an internal voltage regulator. I had the alternator tested and it was bad so they exchanged it for one that tested good. They also tested my battery. It tested good and just needed a bit of a charge. I Installed the new alternator tonight and the guage reads about 14 volts and the multi-meter reads 14.27 volts. I guess I'll see what happens tomorrow when I leave for work.

Problem solved. After installing the new alternator, everything was fine today.

Did you charge your battery before you put on the first replacement? If you didn't, that's why it fried...

Did you charge your battery before you put on the first replacement? If you didn't, that's why it fried...

Yes, I had it charged at the same store I bought the alternator at.