Alternator Woes

[mrbill3]

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?

[fredjacksonsan]

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.

[mrbill3]

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.

[fredjacksonsan]

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!)

[mrbill3]

Originally Posted by fredjacksonsan

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.

[mrbill3]

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

[corning_d3]

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

[mrbill3]

Originally Posted by corning_d3

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.