Does This Sound like a bad alternator

Hey everyone I have an 87 4.0l auto, np242, detroits front and rear, 33" mt/r. I went to pick up some lunch today and the car started great. When I tried to start it a half hour later the battery was dead. After a jump start It started and I drove home. The battery is only 4 months old. I notice that the voltage gauge inside the car was fluctuating back and forth around 13v. Should the voltage be steady while driving? I think I might have a bad alternator. What do
you all think. If i need a new alternator what brand. I dont have a winch yet.

I'd clean up the battery connections real good and also maybe the ground by the dipstick holder. I make sure the terminals are shiny clean and free of oil or grease.

8Mud said:

I'd clean up the battery connections real good and also maybe the ground by the dipstick holder. I make sure the terminals are shiny clean and free of oil or grease.

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x2.

You may just need new cables.

1. Stop double-posting. You asked this in OEM Tech, which is where it belongs. You also asked it in Mod Tech, which is NOT where it belongs, and it doesn't need to be asked twice anyway.

2. Clean up the connections as 8Mud recommends. This means not only the battery terminals but the ends and all the grounds, especially the often-overlooked braided strap between the head and the firewall.

3. Temporarily drop another known-good battery in the XJ and see if it exhibits the same problems. Since it's short-term it doesn't have to be an exact match although the bigger you can throw in there, the better.

All the cables were changed 4 months ago. All the connections seem tight and clean. I was concerned because of the way the voltage gauage was wobbleing back and forth. None of gauges on my other cars wobble at all. They are all steady at what ever voltage they are putting out. I was thinking maybe the voltage regulator was bad. I think on an 87 it is internal to the alternator. Sorry about the double post. I was not sure because I also wanted info on a higher amp upgrade. Thanks for all the info

Lots of new stuff has a light coat of oil on it, to keep it looking new. The small plug on the back of the alternator (tan wire), is known for poor contact, may need a cleaning. You really can't trust the gauge much, mine is about a volt and a half stingy. Doesn't really sound like the regulator or the diode pack.
I can't really remember where the volt meter grounds, but the ground bundle, under the dash, near the drivers side courtesy light is a known trouble spot.

livewire said:

All the cables were changed 4 months ago. All the connections seem tight and clean. I was concerned because of the way the voltage gauage was wobbleing back and forth. None of gauges on my other cars wobble at all. They are all steady at what ever voltage they are putting out. I was thinking maybe the voltage regulator was bad. I think on an 87 it is internal to the alternator. Sorry about the double post. I was not sure because I also wanted info on a higher amp upgrade. Thanks for all the info

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The wobble is AC volts comming from your Alt. This is caused by a bad diode in the alt.

Pull out the alternator and bring it to our parts store for testing. If its bad, pay extra for the lifetime warrantee

If you need a new alt. you might as well toss in one out of a V8 grand or Dodge. That's a common swap and gets you a 136 amp alt. It sounds like you were asking about this anyway... Try a search and you should get some great results.

Heck, here you go... http://www.naxja.org/forum/search.php?searchid=645897 No need to start talking about it again.