Hi, i have had 2 new alternator in the last year. One about 1 year ago and the second about 1 month ago and that one has been professionally rebuilt as well.
I’m still getting low voltage. I had a professional re builder (in the biz 30 years and great reputation) rebuild alt and a new Jaguar specific regulator.


Still low voltage 12.5 and when fans come on drops to 11.2. Will throw ABS code and ASC no traction lights center .
The alternator has had a new wire harness 2 gauge to engine fuse box, all connections tight and clean , no voltage loss front to back, no corrosion.

Voltage starts at about 14.1 when cold engine after it warms to normal operating temp the voltage goes down to 13.7 no load, with load A/C, lights, radio about 12.75 when cooling fans come on at stop light 11.2

we have separated the alternator running from car wiring completely with made up harness. Alternator puts out 12.5 so everything points to bad alternator (not connected to car while running), we took back already rebuilt alternator to re builder and he tested everything again and he came back and said "it bench tested perfect 3 times, nothing more he could do".

We are at wits end, where do we go from here, there are several experts involved and doing this work and diagnosis.
We are stumped!
oh yes, the engine and alternator belts are tight and good condition, no slipage.

Anyone have any ideas ? PLEASE..Thanks

 

A sneaky problem that that happens now and then is a failed and slipping harmonic balancer, you might check it.

 

Thanks oldmots, you know your stuff, but yes it was checked out and fine.

Happy Motoring...

 

check for voltage drop on battery cable feedthru on ECM housing

 

Been there done that, too! thanks

Happy Motoring...

 

Where are you measuring the voltage?

 

I suggest that bench testing can pass a weak alternator on amperage readout. The real test is to put the voltemeter on the battery terminals when the engine is turning at leat 1500 rpm, it should read 14.1-14.4 volts or it is weak. I do know that some ECMs are designed to regulate the alternator, but I don't think this car is set up that way. You could check though. I might mention that running an alternator with no battery takes away the voltage source to charge the windings, so once the residual magnetism is gone, it poops out.

 

The voltage is being checked all over - the ignition wire at the altenator, the battery in and out, fuse box and the cigar lighter.

It is true the ECU DOES NOT control the alternator in a Jaguar XKR. The charging system is extemely simple 3 wires and a case grounding, no ECU or any electronics control the charging system. it is like a 1950's charging system! extemely simple!

We now believe there is a problem with the alternator even though it checks out fine via the re builders bench tests.

The alternator has actually been upgraded to a 4 diode 150 amp alternator.

But now we (they) have found that when alternator is hot the amps are being properly produced but the voltage, when hot drops to almost ZERO, thus the only voltage is coming from the battery, that is where the 11.25 volt reading comes from.

So it has something to do with the heat and the alternator.

Because the regulator has been changed out to a Jaguar XKR convertible ( yes, there is a convertible specific regulator, have no idea why) and upgraded to a 4 diode system 150 amps. the problem must be deep inside the wiring, maybe the stator wire or copper winding.

Thanks for the input to all keep it coming if you have any thoughts.

The shop has spent a lot of time and energy trying to figure this out, very frustrating since this is extremely uncommon. But they say they have a better idea now and will go back to the re builders of the alternator with a infrared thermometer and a heat gun and prove to them there is a heat related problem with their rebuilt alternator.

Out of curiosity:
does any know what a Jaguar XKR 2001 specs. of what the maximum amperage draw should be, being fully loaded with all accessories on (lights, a/c wipers, stereo and engine cooling fans on high)?

so far we have added up about 75 to 85 amp draw with all accessories on. it would be nice to know factory specifications.

Does any one know the amount of amps draw with no accessories or minimum draw of amps cold standing still, just the necessities the car's computers use to check the car systems?

so far we have added up about 30 amp draw with all accessories off, to include computer minimums and the stereo amp at about 10 amps that turn on automatically with the key in the on position.


Thanks and
Happy Motoring...

 

I noted that a weak alternator can bench test okay on amperage and still be no good. The problem is likely part of the upgrade. Trying to force more output from windings designed for less appears to overheat the unit.
It is my experience that rebuilt alternators are a crap shoot. I have bought them and about 90% had very short lives. I can't even imagine the decrease in reliability by trying to hop it up also. I always bite the bullet and buy a new one to avoid reinstalling it multiple times.

 

High resistance anywhere in the charging circuit can inhibit voltage/current. I've seen some mention the ground strap at the battery as a weak point. Easy way to confirm is to use a jumper cable from the battery ground post to a clean ground point on the car.

Beyond that, you should begin by measuring for voltage drops. You do that by placing one voltmeter lead on a battery post and the other lead on a point of similar polarity - e.g. one lead on the battery positive post, the other lead on the alternator output terminal. Or one lead on the ground post and the other lead on the battery groundstrap to body bolt (hint, hint.) Then you operate the device as normal and check the meter reading. Do you see what we're measuring by doing this? If the circuit can't provide adequate 'electrical flow' (please, nobody kill me over that term. I use it for simplicity) the load will try to flow through the voltmeter - voltmeters measure electrical potential/difference - and that difference will be measured and displayed.

If there is a reading of more than a tenth or two (0.1 -0.2 vdc) you have a voltage drop issue and need to determine the cause of high resistance in the circuit. Things to remember: 1) The circuit being measured must be under load (device turned on) otherwise there won't be anything to be measured. 2) The higher the load, the more drop you can expect, e.g. you can expect to see a couple volts or so displayed when measuring a starter circuit but most circuits will/should only toss up one or two tenths at the most. 3) Some circuits have pretty light loads and a voltage drop test won't always reveal an issue, especially intermittents. At that point I usually install a loose headight into the circuit to increase the load on the circuit.

Back to your problem... since you haven't mentioned a starting/slow cranking problem we'll assume the battery positive and ground cables and their connections are adequate. What you may check and find is the wire that runs from the alternator output stud to the battery terminal at the starter has high resistance. Just my WAG.

 

I am having the same problem, did you ever get yours resolved?