1989 xj 4.0 just replaced the alternator as I thought that was the issue but it's still happening . My inside voltage gauge reads 14v but if I hook my multimeter to the batter it bounces around from the lowest of 0.7v to 14.85v. No lights dim. Nothing seams to be effected. The battery gets charged. But what is causing the volts to jump all around. I've cleaned all the grounds and did a rewire kit. I noticed this after fixing my no dash light issue that ended up being in the fuse box. I checked resistance on the grounds and before I hooked the battery up I was getting 0.3 everywhere. After hooking it up and starting the jeep i now get 0.0 everywhere but a couple spots i get 0.15

 

Bad wire on the multimeter?

 

My first thought is also the meter itself.

 

That was my first thought as well so I checked it on my car and the meter is fine. I'm going to trace the two wires that come out off the alternator today after work. I thought for sure the new alternator was going to fix the problem.

 

Is it possible that something with the battery itself could be causing it. I mean I dont think it is because its holding a charge but maybe cant handle the charging cycle?

 

You could have a broken post.

 

Ok when I get home I'm going to disconnect the battery with the jeep running and see what kind of reading I can get from just the alternator

 

Yeah, don't do that.

 

Ok. Didnt know that was bad to do. Guess I'll pull the battery and have it tested

 

So just got done having the battery tested and it's fine. Also cleaned the connector the goes to the alternator. Still the same thing. From what I've been able to find it being an 89 the ecu has nothing to do with it. So I guess its wiring somewhere....

 

It must have been late last night when I was checking the resistance. Because I didnt have it on the right setting the second go round. So now with the jeep running I'm getting almost 5 ohm of resistance. Bad ground or does that mean I have a wire short somewhere?

 

You check resistance with the engine off.

 

Yes. With the battery installed but engine off I'm back to the 0.2 - 0.3 everywhere including alternator body. I'm so lost on what to do next. Wiggled the connector wires while the multimeter was hooked up and saw no difference. I'm going to take the alternator to be tested tomorrow. Leaning towards that not being the problem though. The voltage seams to go 0.7, 5-6 ,7-9,11-14 going fast and hitting somewhere in all those ranges. Just up down up down

 

Can you clarify this a little bit?
So the XJ voltmeter stays at 14.0 and doesn't jump around, and from the operational point of view, there is nothing wrong? What prompted you to check the voltage of the battery in the first place?

 

I got the jeep about 2 months ago. It had a reman engine put in it by the previous owner. The jeep ran like **** after they had it done so it was only drove about 200 miles then parked for 3 years before I got it. First thing i noticed was timing was off. The distributor was 2 teeth off and the firing order was wrong. Fixed that and replaced a bunch of sensors, cleaned and reset the throttle body a few other things. Reset the CPU after changing everything and it ran great until I'd start it again it acted slightly surging. At the same time I fixed a no dashlights issue that was a combo of bad grounds and corrosion in the fuse box. Fixed all of that. Lights work great now. Idk why I ended up testing the battery. But I'm glad I did. It cant be good. I cant find any info on a issue like this online anywhere.