qwain76

So yesterday I used my '98 XJ to go to work and after a little that I was driving, the battery gauge dropped to 9V (only battery gauge dropped, all others were working fine). But the car was driving fine. However, a few miles after the car died (no more electric power). Before it died I could feel it was "caughing" every time I pushed on the gas pedal. I used jumper cables with another car and the car started right away. I used a multimeter and I could measure 13.5V while the car was running. I then changed the battery and all was good. 14V voltage supply and car running great.

Until this morning, I started the car (with the new battery) and after a little bit, the battery gauge dropped again to 12V and then all the way down to 9V. I still had my multimeter in the car, pulled over and measured the voltage and it was 14V (while the gauge was stuck at 9V). Turned the car off and on again and then the gauge went back to 14V.

Can those be signs of a dying alternator? Or you think there is something else I should look for?

PS: weather here is cold (32F) and humid. Not sure if that could have an influence.

Thanks

PatHenry

Before you do ANYTHING else, make sure your connections, grounds, battery cables are all clean and tight. You don't want to be chasing gremlins and firing the parts cannon over something as simple as a loose connection.

If your gauge reads 9 and the ACTUAL voltage is 14, then it's more than likely an issue with the gauge or it's wiring.

Nick-B

It sounds like you've had 2 issues. First a failing battery which you remedied. Second, there is the gauge or rather the electrical connections leading to it. This is a common problem and your volt gauge is not to be trusted. You'll never have a fully accurate reading since the power wire to the gauge is not a direct line to the battery or alternator, rather it makes several stops along the way and there are small losses incurred although not as drastic as only showing 9 volts.

First, thoroughly clean the battery cables and connection points at BOTH ends. I had the same problem on my old '90 XJ and after cleaning all the connections I could, I finally pulled the instument cluster and removed all the little lights and the gauges to where I just had the printed circuit sheet in my hands and then took a pencil eraser and carefully rubbed all the contact points clean and shiny. I say carefully as the printed circuit sheet is a bit delicate and you don't want to fold over or crease any areas as it could actually crack the copper traces. After I did this I no longer saw these large and false voltage drops at the gauge. Even the gauge lighting improved with all the contact points cleaned up.

Best of luck!

Morat

Subbed - I have experienced the same issues. Havn't investigated further yet, XJ needs some other bits done.

DCWinterXJ

Well this is interesting..not hijacking but I was driving to work today and I noticed if I put my heat on high/fan...the batt gauge drops down to like 9 volts! If I turn the fan down to low it goes back up to 14. Same thing with the rear defrost button. I was like hmm maybe I will just turn that off. But as soon as I do the voltage goes right back up. The truck doesn't seem to be affected, all my lights are on relays...headlights and fogs...so they dont mess with the gauge. Just fan speed and rear defrost. I have a new battery and every time I test my Alternator it is solid..and I have covered every ground. I am curious to see what others have to say about this. Oh front and rear wipers also have no effect. hmmmmmmm

qwain76

tiger02

I would check the two connections under the little cover at the front of the PDC. One comes straight from the battery while the other comes from the alternator through an in-line fuse. I would check voltage coming out of the alternator and then at the PDC terminals. I'd also check the drive belt is nice and tight to ensure it is not slipping on the alternator pulley. That's a problem I had a while back in wet weather with no belt squealing to give it away.

qwain76

PatHenry

PDC - Power Distribution Center - it's the box near the battery where the relays and big fuses are.