Ok guys, i thought the alternator problems were behind me, but sadly the indicator light came on again today.
Will be pulling the alternator AGAIN tomorrow, for a checkup - swap.
Normally, an alternator should not break within a month of reconditioning, so now I’m wondering what causes this. I’m leaning towards a high resistance in the + wire from the alternator to the battery, or a bad connection of the ground wire.
Would it be a good idea to run a new wire directly from the alternator to the battery + and a new earth wire (thick) to a point on the chassis close to the alternator?
Do you see any problems with the proposed fix?
But, why not break pout the VOM and see if the alternator is charging.
I made a patch cord for my VOM. It connects via the cigar lighter. Turn on ignition, but do not crank. Read volts. Fire up the engine. More volts? Good. No, not good at all!! duff alternator or open circuit!!
Now you can read volts in real time under different loads and PMs. Can the alternator keep up with more loads. Lights, AC, etc…
Bad cables will impede charging but not harm the alternator, unless they are shorted of course.
A disconnected alt will produce 14v but zero Amps.
Most probably it’s either a bad connection job or bad reconditioning job.
Measure the resistance of the cables to see if there is something wrong.
Running an extra earth wire between the engine and the chassis is always a very good idea.
If you end up needing a new alternator this might help:
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There are tests to be performed in-car, Patrick - before removing/replacing the alt…
That even a reconditioned alt should ‘not break within a month’ is agreed, though worse things have happened. Bear in mind that the warning light is turned ‘off’ by the voltage delivered by the alt - the lamp has no bearing of the actually current it produces, it requires very little current. Adding extra wires may carry more current - but will not do anything to the warning lamp…
As Carl suggests; check voltages as described, at the battery - and do check the connection of the brown/black wire between alt and warning lamp.
To wit; the warning lamp will come ‘on’ if battery voltage is higher than the alt output voltage, and the alt voltage drops with increasing load - or faulty alt output…
I measured 12V directly over the battery leads, engine running or not made no difference.
That tells me that possibly the alternator is not providing current.
After having taken of the airbox, air pump etc I was able to measure on the alternator directly: no charge…
So, the alternator is now out and at the machine shop again. Turns out he was supplied with a faulty diode bridge when he repaired it the last time.
In an XJ6 I suppose you have plenty of room to measure the alternator when installed.
In a V12 with air pump, the alternator is only reachable by people who perform endoscopic operations
Did all the measuring I could, then took the alternator out.
Turns out, the reconditioner was supplied with a faulty diode bridge last time around…
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
7
No, that tells you the alternator is definitely not providing current! With engine running at 1500 rpm, system voltage should be 13.6V-14.4V. Always.
It does not necessarily point to the alt as the problem, though. On the Jaguar V12, we have learned to check the crank damper. The damper can fail in such a way that it no longer drives the alt fast enough to charge the battery.
Bench testing the alternator, there was 0 output, so, I’m relatively sure it’s the alternator again.
The rebuilder confirmed this, he had been supplied with a faulty diode bridge and has ordered another one of a different supplier…
