84 XJS Alternator problem

If you google the Alt. model etc, you may find a connection diagram

This is where I bought it
https://www.oreillyauto.com/detail/b/ultima-4536/charging---starting-16772/alternator-11425/f7cab2ae3cc0/ultima-80-amp-alternator-remanufactured/r111268a/4602873/1984/jaguar/xjs
and this is Bosch version of the same alternator
https://www.carid.com/bosch/remanufactured-alternator-mpn-al315x.html

This has some good discussion about similar problems. If this goes out again I think I’ll get my warranty replacement and resell it and find another brand
https://www.jaguarforums.com/forum/xjs-x27-32/86-xjs-alternator-problems-72794/

Yeah, a lot of discussion about installing a GM alt. That’s a great option, lots of us have gone that route, but it’s worth noting it’s not a bolt-in replacement – unless you’re talking about the air pump, because it’s pretty close to a bolt-in replacement for the air pump! That’s the way I went, using a CS130 alt. Reduced one drive belt. Since I had also ditched the belt-driven fan for an electric fan setup, I went from four belts to two.

Note, though, that there’s an easier way. Later model Range Rovers or Land Rovers or whatever use a Marelli alt that has more amps than the Lucas and is a direct bolt-in replacement.

Is the air pump not needed? Will it affect emissions ? It’s a real pain to have to take both of them off to change the alternator.

Heh. Emissions are a subject of their own. Perhaps worth noting, though, that the air pump only operates when the engine is cold. It must be disabled when the engine warms up enough for the oxygen sensors to start working, because pumping air into the exhaust ports would confuse the oxygen sensors and really mess up the feedback loop.

And there’s no switch to turn off the air pump. It actually pumps air whenever the engine is running. It is disabled when the engine warms up by simply diverting the pumped air into the RH air filter housing – on the engine side of the filter, so when the air pump fails and pukes its guts, those guts go directly into the engine and chunk it as well.

IMHO It’s almost certain that none of the older air pump equipt cars ACTUALLY works. The air rails or ports to the combustion chamber are probably plugged up and have peen for years.

Richard - thank you. I re-read your post. I didn’t previously understand what you were referring to when you said brown/black wire. It is so covered by dirt that I can’t see two colors on it. But I removed the wire from the recessed plug and put it on the external lug (what I was referring to as the sense wire) and it doesn’t draw any current now with the car turned off and seems to start charging without revving the engine although sometimes not immediately. So I guess there should be no wire on the recessed plug. It now actually seems to be overcharging because I measure about 15 volts now when it is charging. But I’ll see how it goes. Also while my voltage gauge on the dash shows in the upper range of normal the red battery warning light keeps flashing on and off. What would cause that?

Kirbert
Does this look like the Marelli alternator that you mentioned will directly fit?

I assume this is the cs130 you were referring to

I dunno what the Marelli alt looks like; I’m just going by reports from others that it’s a bolt-in replacement for the Lucas.

Yeah, that’s the CS130 – although I didn’t go for a chromed version. It will NOT readily bolt-in where the Lucas alt was, but it’s not too much trouble to put it where the air pump was. You’ll probably need to swap in a different pulley, one to fit a 5/8" belt instead of a 1/2", and that’ll mean a somewhat larger diameter because a 5/8" belt won’t bend as tight.

Here is part number for later, more powerful Bosch alternator:


I have successfully replaced old Lucas with this one. It is almost direct fit… newer alternator uses thicker mounting bolt (long bolt at pivot point) so either you need to drill your old mounting bracket or get one from later cars.

This is what I’ve put in my 86 V12, it was a direct fit, and 9 months later I’m still very happy with it.

ALT319
120A
Internal fans.

Original fitment:
Land Rover 90/110 Dhmc 3.5 V8 12V 120A Single V Rib 83-90 Suv

Reference OE/OEM Number:
LRB00367, LRB367, 714/32200, 714/40154, 185046522, 20130212, 63320312, AL2912, AEA2291, 214120852, LRB00291, 20130195, VAP319ALT, ALT319

Also fitted on Perkins 1000-6 HR1, 2, 5 and 1140D-E44TA engines

This is the related thread:

Aristides

The charging voltage is controlled by the regulator in the alternator.
It has an input reference voltage and the regulator tries to adjust the alternator output voltage to match it. Of course the question is what provides that input reference voltage.
It can be a wire coming from the battery terminal which is best, and connected to a sense terminal on the alternator. But it can be simply the output terminal of the alternator.

15V is a bit on the high side, meaning the battery will draw more charging current than at 14.6V which is more typical. The idea is that once the battery is up to normal fully charged voltage it will only take a trickle charge current, maybe 100mA. If the applied voltage is higher the battery draws more current but it is wasted energy, the battery does not store that energy because it is already fully charged. The extra energy is converted to heat in the battery. Not so good.

Measured at the battery posts?

It’s 15 volts both at the battery and at the firewall but it seems to fluctuate about half a volt between 14.5 and 15 My dash battery light flashes on and off like a strobe light. A while back I replaced all of my indicator bulbs with brighter LED versions because I could barely see them. Now I’m thinking that maybe the light was meant to be part of the feedback charging circuit and maybe changing it to LED is affecting the current and feedback.

Yeah, I think your regulator is malfunctioning. Better fix it before it burns up something expensive like your ECU.

Something sounds odd. The usual setup is a standard incandescent globe connected from battery to the IGN terminal of the alternator. There should be a resistor in parallel across that globe. The resistor is low enough to give a decent current to the IGN terminal on start up to energise the rotor and produce voltage out of the stator windings. Then the alternator self excites and the regulator controls the rotor voltage to be around 14.5V. Mission accomplished.

After that the IGN terminal should draw very little current ( or none at all ), have very little voltage across it, and the IGN lamp should be off. A LED typically needs about 2V to glow. Your LED should not be glowing.

Error. It is the resistor should have very little voltage across it.

Yes, but it has nothing to do with voltage regulation. The current through the indicator is only needed to get the charging started. If the car in question really is showing 15V, the regulator inside the alternator is bad.

There was an issue with the IGN lamp replaced with a LED. May or may not be related to a regulator problem.