1989 Jeep XJ, 4.0 liter, alternator issue....


So the last week or so I've been noticing that my lights would go dim and get brighter as I accelerated. I also noticed that my voltage meter in the dash was reading a bit low.

Then, two nights ago I hear a nasty noise under the hood as I'm driving along and my lights and heater lose massive power.

I think, "great, I just threw the belt".

Since it was extremely cold and I only had about a mile to go, I just pressed on while keeping an eye on my coolant temp. I reached my destination without further issue and popped the hood. What I found was the belt was still there. So I took out the multi-meter (I keep a full tool kit in the cargo area LOL) and checked voltage at the battery. It was at 11.88V

Correct me if I'm wrong, but I thought it should read about 14.5V if the alternator is putting out, right?

So I went underneath while it was running and touched the positive lead to the red terminal on the alternator and the black lead to the best ground I could find on the block. The readings were all over the place... from 5.5V to 18.5V. This is telling me that I'm looking at replacing my alternator.

Am I on the right path here? Is there somewhere else I should be looking?


I should probably mention that I've been pushing snow with the bumper all week while driving to and from the deer blind. I had some thought nagging in my mind that I may have issues with that low slung alternator on the 4.0 liter.



Any and all suggestions are appreciated... thanks folks!

Mine is a 99 and I'm having the same issue. I had to plow into my driveway last week and my voltmeter dropped significantly. Going to look into upgrading. Good luck with yours.

Thanks otpracer. It seems like a pretty poor spot to locate such a critical device, not sure what Jeep was thinking with that one.


Anybody else care to weigh in on this one? Am I going about the troubleshoot properly?

Battery should be at about 12.6 when off and 14.5 or so when running. I've always tested the alternator with a multi-meter from the battery terminals. Did you test hook your multi-meter up to the battery terminals while running?

Yes, the vehicle was running when I was getting the 11.88V reading.

Then sounds like a bad alt. if it's not charging the battery while running.