Hello, I'm a serious do-it-yourself mechanic and always have been good with fixing my own cars and troubleshooting, however I am a Jaguar newbie and I can't seem to figure the issue with my 1997 XJ6L (X300). She has about 182k miles on her now.

So here's the problem. The car's voltage seems to dip randomly causing it to chug a bit, either at idle or at low mph. The volt gauge never reads any higher than the 13 but seems to dip dramatically to almost the half-mark between 9 and 13.

Also, at highway speed, say 70 mph, it will hold steady above 13 then drop periodically. I haven't done any voltmeter testing myself, but did have the folks at autozone hook up their tester and they said the charging system is fine, as is the battery. I'm not sure if I fully trust that assumption though, mind you.

In my mind I immediately thought a bad ground, or the voltage regulator could be shoddy, but honestly, I'm not sure what to think considering the intricacies of the esteemed Jag. Ha! I'm also pretty certain the car wasn't well cared for prior to us owning it if that assists any theories.

Any advice would be greatly appreciated!!

 

I would take a set of voltage readings yourself. It could be the voltage regulator or loose connections. Worth checking either way.

 

Adam, there is a wire that runs from the computer to the alternator. THis is known as the field wire. The voltage going through this wire excites the field, which then allows the alternator to create electricity. If this wire is broken inside the insulation, it will make and break, causing the field to come and go, therefore your alternator to jump around. The other option for this is the cable running between the alternator and the battery. Again, if this wire is corroded, it can be weak and have broken inside the insulation. But, where the common weak points are, you would need to talk to people that are more familiar with your particular year car.

 

Well, since it's a random problem, the testing probably wouldn't reveal much unless it took place *while* the random problem was occuring




True on the regulator. And just recently a poorly grounded alternator caused problems for someone here on the forum.

I agree that you'll want to check for wiring faults as mentioned.

Also, is the belt tight?

Also considered the possibilty of the balancer delaminating. That's something that has come up a number of times. I've "been there" myself.

Cheers
DD

 

I'm sorry I worded it a bit wrong. The correct thing to say its it happens intermittently, not randomly. That was my fault I apologize.

And yes the belt is quite tight.

 

Interesting! I'll be sure to try and find what you're talking about. It sounds like that field wire may be the culprit, at least i would imagine the symptoms would be similar to what's going on with our Jag.

 

No apology needed. And, whether random or intermittant, a test made while everything is working normally is likely to show nothing except....everything working normally

Cheers
DD