My one last major hurdle with my XJ6 is that the alternator is not charging. I've done some basic checks like voltage at the firewall studs under the hood and at both under-hood fuse boxes, as well as directly at the battery, and did not find a difference in voltage to speak of. I also had the car up on ramps and did a visual inspection as well as wiggling the connections at the alternator to no avail.. So I'm pretty confident that I'm in need of a new alternator. My question is, are there fuses or relays that I should check before ordering the part? How can I be sure it's the alternator short of removing it and having it tested at an auto parts store? I just want to be thorough in my diagnosis rather than throw money at the problem only to be frustrated by the results later.

 

Check fuse 10 on the RH engine fuse box as this powers the voltage regulator to make alternator power

 

The voltage regulator veries the excitation voltage to the magnets in the alternator for it to produce alternator output of around 13.5 volts which is above a fully charged battery of 12.77 hence charging .

Only read this value at the spinning alternator large " B " post and not the battery

This one fuse is tapped by other systems that can be remove from the circuit to determain what sucks it down and pops the fuse

The voltage regulator is a # IN435 but I never could get one that worked out of the box

The alternator can be removed from the top and spun up on a tester at any automotive parts store to determain if it's good as a stand alone alternator/built in regulator .. The mounting pivot bolt is removed from the bottom . A shouldered bushing stays in the clevice bracket . The clevis can pinch the alternator so a large screwdriver can leverage it out of the bracket . See link pic below

https://www.jaguarclassicparts.com/u...-3-2-4-0-litre

Keep track of the small wires on the noise suppressor hookup ( capacitor ) as polarity maters . This capacitor can easily be tested with a common meter

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Thanks for the replies, I will try to check voltage at the alternator in the morning whilst changing out the oil and coolant. I did check the fuse specified, which was not blown nor were the blades corroded. It's still not charging on it's own so I've been keeping my auto-sensing battery charger on it to save the battery from being drained completely.

 

Well in the midst of tackling the previous oil change done by He-Mans garage, where I had to use my foot to break loose the drain plug, and ruined two screwdrivers removing the oil filter, after my filter wrench failed to do anything but crush the filter housing...I was so fed up and irritated that I forgot to get the meter out while the car was in the air.. So I have ordered a brand new alternator and 2 brand new belts, and will install them when time allows! I will let everyone know if any complications (ie not charging) occur after/during installation.

 

Hi 96x300 , looks like my comment is to late, but was going to suggest checking out a local specialist who could advise if it is viable to have your alternator rebuilt, I went down that route a couple of years and it's been fine since and made a big saving over a new one.

 

I thought of that, but the only place local to me that offers this service seems questionable, and is open by appointment only. I have another vehicle to drive until the Jaguar is ready for daily use, so I ordered a new aftermarket replacement online for $108.55.

 

The B terminal on the alternator is from the top side

 

I didn't really see how to access it around the smog pump with the engine running I guess, I over think these things sometimes. I'lI take a closer look when I can.

 

No need to remove the thick battery cable so you can leave hooked up

The rubber terminal boot scoots to the side

You can use a metal probe like a metal coat hanger if hands to large . spoon ?

Looking for at least 13.5 volts DC

To double check the fuse the # 1 is the one closest to the terminal post on the fuse box , and the next row closest to the king relay is the 9 or 10 , can't remember

If you have to change the alternator don't turn in the core just yet as they have a reliability issue out of the box . Have them spin the new one on the stores machine first and let it run for awhile to warm up the voltage regulator as this is where they fail /

The alternator is a rare 120 amp original Denso brand that takes a couple days to order up .

 

Due to my other mishap regarding the broken thermostat housing, and my lack of desire to waste any of the coolant I just out in or drain/recycle it, testing of the original alternator, and testing of the new alternator once installed, are out of the question. Mid-week my replacement will be here and then I can start the car with my fingers crossed! Overall my installation went smoothly, aside from the fact that the high today was 39 degrees. The alternator is "Power Select" brand and is an aftermarket new unit, manufactured in China. I like to avoid Chinese parts as much as the next guy, but I've had good luck with them and it's what the budget allowed. Out of the box I could find no major flaws in quality or difference from OEM, it spins very smoothly, and according to the included test sheet this unit peaked at 172 amps! I also replaced both belts with new "Bando" units, as the others were old and dried out. I've ordered this brand before and find them to be well made and quiet running. Luckily for the a/c belt the tensioner was clean and free enough I was able to loosen it by hand after a couple turns, and I happened to have an 8-point 3/8" 1/4" drive socket which fits (backwards) perfectly to tighten it up.

As soon as I can I will let you all know if everything is indeed all and well now, or if I have work to do and/or parts to return! For now, here are some pictures.

 

FYI, it's probably just a voltage regulator that died, maybe brushes and in a worse scenario a bridge rectifier, all three together cost ~$50 to replace and are very easy to swap.
I'd keep the original and repair it, Chinese are a hit and miss, some work well and other will fail within a month, QC is pretty much non existent there.

 

I still have the original in the new box set aside, I was thinking about getting the parts to rebuild it, run to the parts store to have it tested when I'm done, and then put it on the spare parts shelf.

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Well.. yay for shiny new part install.. but after being able to start the car this morning, voltage was still not indicating that the system is charging (12v and slowly dropping). So it looks like I will have to get out the multimeter and check connections when time and weather allow.

 

Possible dumb question -- but -- on mine, the crankshaft damper pulley had separated and was not spinning the alternator fast enough. Discovered this when installing the third alternator.
Other posts on the forum recommend painting a white stripe across your bottom pulleys while the motor is stopped and check later to be sure it's still in alignment.

 

Excellent suggestion, Lee. It is very common for the crankshaft pulley to become delaminated at middle age. The immediate result is a no-charge situation, as you know too well. Shortly after, the battery will die and the car will be stranded. A new battery will not help. Nor will a new alternator.

A failed crank pulley is usually accompanied by some noise. Either a loud screeching at startup or acceleration (which might go away), or a squeal or rattle at idle. Always with little to no charging showing on the gauge at idle speed.

So 96x300, paint that stripe across the pulleys, drive the car once, then shut off and check for alignment. This is a must-do to (hopefully) rule out a bad crank pulley. For now.

But don't worry, the pulley can be rebuilt if necessary. It is a well-documented procedure here. Most need it eventually. All three of my Jags needed it. The current car, only last May, at 95,000 mi. It is not any kind of a deal-breaker.

 

Thanks for the tips guys! I will look into it , inspect the pulley, and probably do the stripe. I went outside to start the car and let it run for a bit, since it's been extremely cold the last few days, snow, etc.. After 2-3 minutes with the headlights on it just decided to start charging! Maybe the alternator needed to wake up a little bit? Test sheet did say 2015 so this alternator sat on a shelf for a few years.

I only had ran it for maybe a minute tops before as I was on my way out the door to work.

 

i think my Ford laptop computer is slipping There I fixed it

 

 

The alternator doesn't need a wake up period! What happens is when the pulley warms up, it expands a bit and can then grip the grooved ring better, which then turns the alternator at the right speed.

If this happens every time you start the car from cold now, it only reaffirms whats happening. Unfortunately, it will not go away, it will only get worse. It will probably cause stalling at idle due to lack of power. Especially when you're running lights and defrost/heat. Eventually the battery will die.

Sounds like bad news, although nothing is definite until you mark the pulley and give it a drive. If the pulley is bad, the alignment of the marks will go off quickly, perhaps right away after you start up. But you have to do this before you assume the new alternator is bad.