Last week I went and drove an '85 coupe. Drove beautifully, everything worked except the heater (which I already have direction on). NO rust. So, I traded my old pickup truck for the '85 plus an '84 parts car - what a deal! My wife and I drive down to pick up the Jag today.

Maybe not so much of a deal. The guy had to put an old battery in the car, one that he said would "get me home". So, we jump-started it with a large battery charger set to "start" and I got home (about a 20 minute drive - 15 miles or so) and the car ran very well but charge was on the very bottom edge of "normal". I figured no big deal, I already knew the battery was bad. Went to Advance to get a new battery and surprise, they actually had one on the shelf. Put it in, still no (low) charge. Getting 12.3v at idle on the battery terminals, and when I step on the gas, the volt gauge rises to about 13 and then drops back off when I let off the gas. I suppose it is possible the new battery needs to be charged to read normally, but not likely.

The charge light remains on all the time when the car is on. The light does NOT remain on when the car is shut off. Thoughts?

Second issue - when I drove the car the brakes worked perfectly - took it on a 15-20 minute drive including a couple hard stops. Drove it home, again brakes were fine. However, it seemed like once the car actually warmed up to N I lost pedal, and it only stops in the last inch or two of pedal travel. Still stops pretty well, though. Thoughts? Is there a booster vacuum issue as the engine warms or did I just blow out my master cylinder on the way home? I haven't tried it again since I got home.

I've always loved Brit cars and Jags in particular. I'll never have the money for an XK120 but this car is my start into the world of Jaguars. I am a much-better-than-average mechanic, having done a couple of frame-off restorations on domestic trucks and cars. Most of my questions here will be standard fare, just looking for what is "different" about the Jags vs. your average domestic classic.

Thank you all for your help!
Darel

 

If it matters, the light I'm getting is the lightning bolt - the overcurrent light. Didn't realize there were two separate lights until I did some research? Does that change matters - probably still an alt / VR issue since I'm still only getting 12.3v at the battery when running.

Or can this be an indicator of a bad load wire on the back of the alt, failing to send a charge back to the system but ramping the alt up 100%? Where does the overcurrent light get its' measurement from?

 

The lightning bolt on my car was on constantly when I had a bad alternator. With a new one it lingers for about 10 seconds after startup. Your Voltage gauge should read at the top of the 13 at the normal line. It's ok if it goes down a little while running systems that put a load on the battery I.e aircon, defrosters, headlights and the like. I do not know the voltage at the battery while my car is running but 12.3 is too low for sure. The electrical system the Brits put in the xjs is nothing more than is necessary.... If you've got the parts car swapping alternators could be a good start?

 

With the car running I would expect 13.5 to 14.5 volts at the battery depending on state of charge.

With the battery disconnected and fully charged it should be around 13volts. 12.3volts the battery has around 40-50% charge.

Also it would help if you put the model of your car in your signature. There were a lot of changes to the XJS over its 20 year life I6 V12 and also different instrument clusters.

cheers
Warren

 

Thanks guys. I was avoiding pulling the alt before I knew it was bad because 1. I hear it's a giant pain, like everything else under the hood and 2. I won't be able to arrange for a trailer for the parts car for a couple of weeks, so that means I need to drive half an hour to go get the parts car alt and lay in knee-high wet grass to get it out. Plus, there's no guarantee that one's good too.

 

those batteries come off the shelf charged. your alternator has low output. you could have the guys at autozone test it.

 

Update:

I went out to work on the car this morning. Fired right up with no hesitation at all - good thing, no battery drain to chase.

Both battery lights initially came on. Then, I was left with just the lightning bolt like always.

Checked voltage at the cig lighter, 13.3v! Gauge was at the rock-bottom of "normal". It comes up when I step on the gas a little.

Voltage at the batt was likewise about 13v. Not great but it's doing something. My plan is to pull the alt out of my parts car and have it rebuilt, since now I'm not in a massive hurry for it. FYI the lightning bolt and the orange "secondary warning" light stay on all the time.

And, surprise surprise, I had a good brake pedal! I drove the car to my buddy's shop for an inspection (hadn't been driven in 10+ years) and an oil change, and surprise again, it passed inspection. HOwever, my brakes did lock up on the way down there. I figured out the pedal is not retracting. After I step on the brakes I have to lift the pedal up with my foot, and it takes some force. I'll start a new thread about the brake pedal issue.

After the 20-min drive the volt gauge did seem to come up a bit, with no accessories on it hovers just a hair under the "M" in "normal". It doesn't really seem to get solidly into "13". It doesn't crank slow or anything.

Guess I ought to still replace the alt but now it doesn't seem to be an emergency. I suppose I'm getting enough charge to keep the car going for a while.

Thanks,
D

 

I would look at using a newer GM alternator, the later Marelli cars used a larger (130 or 140A) alternator. This is good upgrade and could be cheaper than rebuilding your older Jag unit

 

I remember a long, long time ago you could ask them to "amp up" your alt while rebuilding - as long as the case supported a higher amperage. I was planning on inquiring about this. I'll check into the later alts, I did look into the Land Rover alt that's mentioned in Kirby's book but MUCHO $$$$.

Do the later XJ alts bolt right in place? I do want to keeop the car somewhat original, not keen on pulling stuff out to squeeze a CS133 in there.

Thanks,
Darel