Sorry I've been delinquent in not being here on this thread. During all this pandemic crap I parked my 88 XJS V-12 in the garage carport where it currently sits. I've been good at starting it periodically to make sure the engine warms up and then shut it down again. A couple of weeks ago it started up reliably like it always has but the alternator gauge show no output voltage at all. Looks like it died on its own while sitting there. I've never removed the alternator before but it looks like a daunting task that probably has to be done from underneath the car while it's up on jack stands. Other than put a voltmeter on the battery to measure output voltage at idle speed (battery shows its 12.4 volts only) I'm not sure what else I can do except remove 4 belts from underneath and remove the alternator.for further tests.
Question, has anyone got any further testing ideas or had any experience with this kind of problem? I'm definitely not looking forward to this experience!! .................thanks, Mike in College Station, TX . .

 

Forum search is your friend.

 

Hi 51 rover

Never mind the Alternator, as I would rather Climb Mount Everest in a Pair of Carpet Slippers before taking off those Belts as having gone and done this once its a job I never ever want to do again!

As its such a 'Nightmare' that it has to be one of the only jobs that I'd ever let a 'Shop' do

So the first thing to do is to get yourself an Alternator Tester, cheap as chips on ebay about $10 and though you may only use it once, its certainly money well spent as the indicator lights will show you where its at

At the end of the day its probably nothing more than a dirty or greasy connection, or worst case scenario a Diode may have blown, which your Alternator Tester may well indicate

Paul (ptjs) has had a very similar problem on his Car, so he can almost certainly show you how to fix it

 

Mike,

A couple of thoughts:

Unless you've installed an additional gauge, the standard gauge in your car is not an alternator gauge, it's a voltmeter. It's registering the voltage as maintained at battery terminals. You would need an ammeter to show alternator output (in amps). As your car started, the voltmeter would register at least 12v if reading correctly. So, if the gauge is genuinely showing zero, you would seem to have a gauge problem as there must be some volts in the battery. As regards measuring the efficiency of the alternator by putting a voltmeter across the battery, then remember that the alternator is quite likely to be not really achieving much output at idle. Therefore 12.4v battery voltage at idle isn't necessarily a problem. So a couple of questions:

- Is the alternator light extinguishing, at idle, or when the throttle is pressed?
- What voltage do you read on a voltmeter measuring the battery when at, say 1500-2000 rom?

I wouldn't condemn the alternator just yet until you really know that it's not producing any output.

Good luck

Paul

 

Thanks Paul and the others who replied with encouragement and good ideas to follow up on on this alternator issue on my '88 Jag alternator issue. I'm going to bring the car into my shop garage and do some more testing, like looking for high resistance ground connections, and literally anything that would keep me from having to remove the alternator unless absolutely necessary. I'm also going to get the alternator tester too. I didn't know they made one that actually worked. ..................thanks to all, and I"ll keep you informed as to what happens. ...................Mike.

 

I'm with Paul on this one. Just measure the voltage at the battery with a meter, car off, key not even in the ignition. You may get like 12.5 V or so. Then, start the car and take a reading at the battery. If its HIGHER than with the car off 13.4, 5, 6 ,7 V etc then the alternator is working and charging.

It's most likely a problem with signal wire from the alt or the contact at the dash instrument cluster or the guage itself.

Have you BANGED on the dash yit,,, lol?
That's what I would try first.
Needle prolly got settled down there while the car was parked up. It got comfortable

 

Don't be afraid of taking the altenator out the bottom. If you have an air pump and your belts are good and don't want to remove all of them, you can easily get it out the bottom by removing your sway bar end links and the oil cooler line from the bottom of the engine. Wheels up, off and sway bar end links out takes about 20 minutes. Find my landrover alternator thread, it has the details with pictures.
that oil cooler o ring is usually leaking anyway.

 

Update on my alternator issue...... Turns out that one of the suggestions in the replies here is correct and I didn't have to remove the alternator. Looks like it just sat too long before being driven again. I fired it up yesterday and the gauge came to life showing what appeared to be a low voltage output from startup but then when driven around the block the voltage came up to full charging voltage at idle, which I verified with a voltage check at the battery, 13.6vdc, Looks like I probably have a corroded ground connection in the instrument circuit and need to check out all the connections anyway. BUT, the old girl gave me a real scare when I drove it around the block because when I turned the corner I shoved the accelerator to the floor, only to have it stick at full throttle. I couldn't get my toe underneath the pedal to stop it so I let it go full throttle back to the house with my foot standing on the brakes to somewhat control it and then shut it off in front of my house. Then I reached down with my hand and pulled the throttle pedal unstuck. I fired it up and it ran fine. Looks like I have some linkage to inspect and find out what the heck made it hang up. I'll get that done soon. As a side note, this car has always been garaged and out of the weather completely but had to put it in a carport (roof only) until my garage shop expansion is done, which will be finished soon. Then it goes back inside, so maybe the old girl gave me a heads up to hurry and get it back inside.

 

And thanks Xjeffs for the info I'd need if I had to remove the Jag alternator. I'm going to check out your LR thread as suggested and take notes. I'm not sure what year your LR is but mine is a 1951 series one that my dad bought in 1951. But hey, no alternators on that one!!

 

Glad it's sorted (well almost!) and that you got home safely with a stuck throttle pedal!

Well done!

Paul

 

I learned a long time ago that when you get in an old car, British or otherwise, that you should be prepared for anything possible to happen. Normally in this case I would have just shut the engine down and be stuck on the side of the road but the thought of possibly towing it home made me want to "ride the old girl" home if I could control the engine with the brakes. Of course now, my new brake pads now have an untold miles of ware on them. I suppose that the good thing is that the engine still has a few drops of oil on the pavement underneath it so everything else is normal!. ....................Mike.