2001 xjr, bought it last week.

ran some tests, everything looked good except the battery was receiving low amperage from the alternator, ok, had the alternator changed, still low amperage... went back and bench tested the old core, passed just fine. now it is narrowed down to something between the alternator and the battery im assuming.
what could it be?

note: on the navy base we have a shop we can use with lifts and tools, so i have plenty of tools at hand

 

Forgive my ignorance of your particular model. Do you have an Amp meter on the dash and it is reading in the red or low?
It would be normal for a battery to draw low current when it is fully charged. What caused you to check the current?

Joe

 

we used a battery tester, with the car running the voltage is 12.66 and the amperage from the alternator is 30amps. with the vehicle off the batter is 12.54 but that is after getting a jump and driving to the auto parts store to get it tested

 

from my research all i can find is that it could be the engine ground strap, which i haven't checked but i will this coming weekend

 

I am not sure where Jaguar places the voltage regulator, but that battery needs to recieve higher voltage to charge. Most cars I think it is around 14 volts to charge a
12 volt battery. Any autoparts store will check it for free.

 

Most common problem is the joint at the stud on the RHS false bulkhead.

The power distribution on the car is actually in several segments of cable. As a result, there are lots of joints to check.

 

where might i find a wiring diagram or pictures, to locate those joints such as the stud to rhs false bulkhead?

 

search false bulkhead in this section for pictures

the electrical diagrams can be had standalone or as part of JTIS as downloads linked from the stickies.

 

I don't understand where this 30 amps comes from.
Did you put a DC ampereclamp somewhere?
With just the ignition on and the engine running the car shouldn't draw anywhere near 30A.

 

What is the condition of the battery itself? Leave the vehicle for a few hours with the engine off & then measure the battery voltage. It should be above 12v & ideally above 12.5v. If it's well below that then either the battery is flat & needs recharging before doing any alternator tests, or the battery has a dead cell which is dragging down the main system charging voltage from the alternator.

Once you've confirmed that the battery is alright & fully charged, then you can begin investigation of the charging issues. With the engine running, measure the voltage at the battery itself & then directly at the output of the alternator.

If you're getting around 14v at the alternator but only 12.5v at the battery, then the problem is either the engine ground strap or the false bulkhead connector having high electrical resistance.

I'm wondering if there's a problem with the battery, as an engine idling with no heavy electrical loads would not require 30 amps from the charging system-it would normally be less than 10 amps or so.

It looks like the alternator is putting out a decent current to maintain the system voltage, but something is dragging it down & that's usually the battery with a failed cell etc...

 

got off school early today and to it to the hobby shop threw it on the lift, first thing i saw was the engine ground strap, scotchbrite pad and some cleaning, battery not charging went away. went ahead and did the same to the rhs false bulkhead stud connector also, thanks a lot.

also i let the car sit and then tested battery, 12.54v so thats good

Thanks,
MM3 Moroz

 

Another success story at no expense. Good work. When I was in the Navy back in the pre- Vietnam days my ship spent a couple of summers at the Philly yard. They had a great hobby shop there and we rebuilt a friend's Healy 100-4 engine and gearbox while there. They even had Whitworth taps & dies.