First off hey new to the forum but have been reading threads for about a year now (since i bought my jeep)
I have a 98 xj 4.0 with the automatic trans. My problem started with one night I was driving and my battery gauge dropped to nothing and when I pulled over and turned the Jeep off and restart it it would shoot up to proper voltage and then did the same thing the next morning. I work at oreillys so I checked me alternator and battery the next morning and the alternator showed bad vr and battery showed good. So I took the alternator off and retested it on the machine to find the alternator it's self is good. Now (2 days later) the Jeep half the time on start up shows only 12 volts on gauge and then after a minute or two drops to none and the other half shoots to 14 volts and stays there. Everything I've read shows the vr in the pcm isn't common to go out so I'm hoping for a ground issue. I have Kelley WiPs mains upgrade and a 136 amp alternator going in in the next few days but wanted to know what else I should look at if that doesn't fix it. Also I have checked the battery with a volt meter and when the gauge says 14 I have 14 and when it says 12 or nothing I have 12 so I know something is actually not charging and its not just a gauge gone rogue. The jeep has yet to not start or shut off but I wanna find this before it gets to that point because stuck in high 90 weather will surely suck. Any help or advice would be awesome thank you guys in advance.

 

The '98 alternator should have an external ground cable that goes from the alternator to a coil mount stud (G103). See if it is secure.


The other ground cable, at the other coil mount stud (G101), goes to the battery negative post.

 

You sir are a beautiful man crawled under on lunch and the alternator terminal is barely hanging on and the battery terminals pretty rough I'll fix it once I get off and hopefully that will fix her up. Thank you.

 

Let us know please. It helps others to read a follow up fix (or not - LOL).

 

I'm not sure what cables come with the Kelley kit but if it has a giant cable to go from the firewall to the cylinder head stud, you don't need that.


I see you work at O'Reilly so I suggest you get the Dorman braided ground strap and use it. It reproduces the OEM braided strap. See pic.

 

Ken, Ken, Ken, I keep tellin' ya, that big ground on the firewall is good for at least 10 HP, 7 or 8 MPG, and it will keep your ashtray clean, too.

It's been known to make bald men grow hair, too!


Okay, seriously Brute, listen to da man. That particular ground gets ZERO benefit from being oversized. The braid strap is better than any cable.

 

Lol I've seen some back and forward about that wire and since I actually have that exact strap sitting in my tool box still brand new I'll use it instead. I will let yall know what happens with the charging but it will have to wait till tomorrow morning since it's decided to monsoon every 20 minutes here in the blue grass state.

 

Well still on the hunt for an answer cleaned up that ground but no difference doing the wire upgrade eventually maybe that will help

 

Well after a battery under warranty and a new alternator she's back and running... it's odd because both checked good off the vehicle but when put on the Jeep it was showing a bad vr gonna get the new wires in this weekend and move on with a confused look just happy she's running again it's strange to wave at jeeps and they look at my Nissan with confusion.

 

Glad it's running again.

Now, please learn the value of punctuation.