Hi,
I recently replaced the alternator on my 1996 XJR as the old one had seized. The new one is fitted and I think the wires are all in the same order as before. However now the battery warning light is on, the battery reading on the dash shows that the power from the battery is decreasing and although the car starts and idles, when I try to drive it it has no power, only goes to approx 10mph and splutters. I took some battery readings and the battery is strong. However the reading from the battery leads with the engine running shows the power level is going down.

Does anyone have any ideas what could be wrong?

 

AHA, you are NEW, WELCOME.

I woulkd be seriously doubting the integrity of the replacement alternator.

When you say "new" are you referring to NEW from Jaguar, or a rebuilt unit from an electrical outfit.

Some of the replacement parts they use are not matched to our system. I say that purely from dealing with an XKR (same alternator as ours, and Toyota Landcruiser down here), my mate had rebuilt, and he had similar issues, and the rebuilders were at a loss, so he rectified it by refitting his OLD regulator assembly, problem solved. We have determined that the regulator they used is suitable, althogh does have different wire connector points, but simply would NOT work in his car. NO IDEA why, it just dont, and now with the old one in there it is fine.

Just to eliminate any issues with the car, I would remove that alternator, go to the rebuilder (if its theirs), and have them "bench test it", and give you a print out of the readings. If its a NEW from Jag, do the same, as the readings will be required for a claim on Jag.

 

I agree with Grant. And furthermore, be suspicious about another replacement from the same vendor. It was quite a while ago, but more than one poster here claimed they got a second or third unit from the supplier, and all failed to charge, The suppliers claimed than "proved" the vehicle wiring was at fault, when in fact, the replacement regualator integral to the alternator was missing some control function needed spaecifically for the X-300. I don't recall what that feature was, nor do I have my schematics here to check, but assuming you have checked the buljhead wiring terminals for tight, and had a look at the battery and engine ground straps, Grant is almost certainly correct.

 

New to jag, but by no means new to car problems I had battery issues for years on my previous BMW. Replaced battery and had three (!) alternators over the years, but no help. Turned out to be the regulator, that for some reason was very hard to match up to the car. New, used, orig or whatever, none helped, until I finally got lucky with a used one. So weird...

 

Hi, Thanks for the replies. Do you think that if the new alternator (bought from Lucas) is faulty, it would cause the car to run so badly?

 

Jonathon:
These cars are somewhat unusual in that they do, in fact, have control problems when the supply voltage is just a little low. Some among us theorize that it is a problem that develops after time, with aging power supply capacitors (condensors to you limeys out there!) being the culprit, but that is only conjecture AFAIK.
If the problems are apparent at idle speed, you can run the car while connected via jumper cables to another car with a known good battery and see if th eproblem clears up. Or just temporarily move a good battery in for testing.