Greetings,

I am working on a 2000 Jaguar S-Type, 4.0L V8, with a 3.1Amp draw in the charging circuit (key off).

When I backprobe the 4-pin connector at the alternator I am seeing battery voltage at the red wire, and about 4.5V at the Grn/Blu wire KEY OFF. The other terminals measure 0 Volts. If I am looking at this correctly, the Grn/Blu wire is the sensing circuit, is supposed to be hot in start/run, and should not see voltage with the key off... battery volatge at the red wire is normal.

When I remove the connector from the alternator, the draw goes away, and there is no voltage present at the Grn/Blu pin.

Does this obviously point to an internal defect in the alternator? Does it sound like I'm overlooking something here?

I will note that the alternator on the vehicle is Bosch #AL9403X, which they (Bosch) claim to be a remanufactured, OE Nippondenso unit.

Any help here is appreciated. Thank You.

 

I'm impressed. You've found a 3amp leak in the alternator. This is wrong of course. There should not be ANY leak this big. The manuf. allow a few milliamps permanent draw for safety circuits such as alarms etc., but 3amps is far too much.
It sounds like a defective/wrong alternator to me. The alternator works by having an energized rotor or (armature if you like) just like a universal motor, excepting that instead of a commutator you have two slip rings. The control unit for the rotor's energizing produces in the order of 3amps or so normally. The more current here, the more magnetic flux, the more current is generated in the stator coils, of the three-phase type. The a.c. is rectified by six stud rectifiers in the earthy end of each of the six coils to ground on a rectifier plate which also serves as a heatsink. The whole point of it all is that you don't have a rotating switch, a commutator, in the heavy current path of up to 80amp. to the battery like you would with a generator. The slip rings only have a few amps. An alternator also is capable of heavy current charging even at low rpm., and attempts to keep the battery at 14.4volt., a constant-voltage charging system. So....it looks like a new alternator. DO make sure the alternator fitted to the engine is the right one! Some designs have the control unit external to the alternator! I'd also look for any relays in the charging area to see they aren't jammed or otherwise malfunctioning. Best borrow an alternator and hook it up to make sure it really IS the alternator before spending the hard-earned.
Leedsman.

 

That's definitely a sign of a bad voltage regulator. I had one fail in my X-type, and the car would go over voltage when charging. At least in the X-type, the voltage regulator was internal to the alternator. I actually killed a battery in a couple days not realizing this. I replaced the battery first, and the bad alternator tore right threw the new one (thank god for replacement warranties). The 4.6 v at the sensing wire is interesting, that sounds remarkably like the clamping voltage of a zener diode to me.

What does the charging system voltage look like when the car is running?

Do you have or do you need the electrical manual for the car? I can e-mail it to you if need be.

George

 

I've got 15-20 pages of figures, and wiring diagrams that I was able to print from an electronic source, but I have noticed a couple of inconsistencies: fuses out of order at luggage copmartment, pin numbers between the generator and PCM not corresponding (off the top of my head).

What I would really like to see is an internal schematic of the alternator itself; specifically the voltage regulator. The best I could come up with were a couple of generalized ones from the source mentioned above, and an automotive textbook I have. If it is easy enough for you to e-mail the electrical manual to me then yes, please do, and thank you.

With the car running, I turned on the radio, highbeams, and the air conditioning, and measured 14.1Volts at the battery. I didn't take a reading at higher RPM, but this seemed reasonable enough given the type of problem I'm looking for (no?).

I should probably add that I forgot to backprobe the Gry/Red, and Wht/Red wires which lead to the PCM at the alternator. I only checked for voltage at those terminals with the connector removed.

The thing is here, I'm an automotive student, trying to help out a family member when I have the time, and can get it up on the lift with test equipment. To make matters worse, that family member had a no-start issue a few months ago which lead them to replacing the battery, and then the alternator; hence the Bosch unit under the bonnet.

All of your help is appreciated, and again, thank you very much.

 

I would be glad to send you the electrical manual, however I have no way to get in contact with you. If you can send a private message, send me your e-mail. Otherwise, make a useless email (gmail, yahoo etc) and post it here and I'll send it to you there.

Thanks,

George

 

Here we go: jaguarstype00@yahoo.com

Whatever I figure out, I will post back with. Thanks again.

 

Check that email I sent you the guide.

George

 

I said I would post back with what I found so here goes:

I informed the owner that the remanufactured Bosch alternator that he had installed was defective, that it needed to be replaced, and (strongly) recommended the application-correct Nippondenso replacement unit. A couple of days later he called me back and said there was a new alternator waiting for me at Napa... I drove down, picked up the Bosch reman unit he had paid for (identical to the failed unit, and despite my recommendation), brought it back, installed it and..... 3.1amp draw was still there.

I spent several more hours pouring over the wiring diagrams, probing every junction of every circuit that tied in, and maintained that it had to be the alternator. At this time he had me wire in a disconnect switch for the battery just to keep the vehicle driveable, and they went on their way for what has been almost three years now...

In the last couple months the vehicle quit running. The car was taken elsewhere for diag/repair where it was determined that the replacement-to-the-replacement alternator failed. The alternator was this time replaced with the correct Nippondenso unit and..... low-and-behold: PROBLEM SOLVED!

Thanks again to those who chimed in.

 

wow, i'm amazed you remembered to post back the outcome after all this time, you have a far better memory than me !!!

I forget what i've posted as soon as i hit the post button

 

It's gotta feel good to find out you did not miss anything!!! When a part is bad out of the box it's so hard to believe it's bad. It has to be something else.

Great memory!
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My entry of 2/20/2010 was therefore a bullseye.
We had this similar problem with new parts out of the box in the electronics business. A certain logic-gate chip in a microprocessor controller for video jukeboxes was proving troublesome. As soon as I lifted the +5volt supply a little, the problem disappeared. (TTL logic of course). However, when I fitted a Motorola chip instead of the 'recommended' one and reset the +5volt correctly, all problems gone. The Motorola chip also worked properly at LESS than the normal +5volt. Both chip specs. were the same, especially re. access times. Can't beat quality manufacture can you?

Leedsman.