Hello All,

The latest quirk with my '99 XJ8L is that I'm only getting a hair over 12V at the battery when the car is running. As a result, the battery is slowly running down until the car can't start.

The mechanic tells me that the voltage at the alternator is correct and he suspects some sort of wiring problem, but has no idea where that might be, nor do I.

Could this be a grounding issue somewhere? Is this some sort of common problem that those who've already experienced and fixed it can easily recognize? Any guidance would be appreciated.

 

It can be a problem anywhere along the complete power distribution circuit. Excessive resistance anywhere in the path will keep the alternator from sensing the true charging voltage at the battery.

A first point approximation lies in two measurements:

- voltage between alternator output stud and alternator case
- voltage between alternator output stud and chassis
- voltage between battery stud on engine fusebox to chassis(this is the farthest point away from the alternator output)

They should be the same. If they are different see below. Otherwise, this is your baseline voltage.

Further diagnosis involves making voltage drop tests at major points so that it can be deteremined where the suspect areas lie.

The full power charging circuit is:

- alternator output stud
- starter power stud
- false bulkhead stud (very common failure point)
- main power distribution block at rear of spare tire well
- positive battery post
- negative battery post
- negative battery cable connection to chassis
- ground strap from chassis to engine block at right hand side of transmission bell housing
- engine block to alternator bracket interface
- alternator bracket to alternator case

excessive resistance anywhere along that path will float the alternator regulator sense circuit above the voltage actually seen by the battery. This will lead to a low charge state on the battery.

The first three and last two interfaces are often avoided in testing because they are hard to get at. They are also almost never serviced. I suspect many alternator replacements "fixed" a charging problem because r&r of the alternator scraped the surfaces clean.

On mine, all of those interfaces have been disassembled, cleaned and reassembled with conductive paste applied using polishing motion with abrasive paper as per instructions. ($4 tube of OxGard from Home Depot) This is *not* the same as dielectric grease which is an insulator. Dielectric grease can be used on the *outside* of the joint to prevent water ingress but not in the joint itself.

In addition the power feed chain from the main distribution fuse panel at the spare tire wheel well to the fuseboxes have received the same treatment.

This treatment should result in years without corrosion related power problems. The problem is that it can take days to do this right including hauling out the alternator bracket.

caution: The power feed studs on all of the fuseboxes are very weakly embedded in the plastic. As a result, excessive force can cause the bolt head on the "stud" to cam out of the hexagonal depression and require a new fusebox which is "no longer available".

 

Plums, that is an excellent assessment of the entire charging system and it's paths....onme of the best i've come across ;o)
I performed this excact scenario about sisx years ago and have never had a problem since.
As these cars average 12-15 years old now, it's nearly always down to lack of common sense maintanance that creates 98% of 'problems' that occur on forums such as this.

 

Hello Brian,
Along with Plums excellent assessment of the situation, you can apply a simple, quick method of testing for voltage at the battery with a simple volt meter.

Test for voltage at the battery posts with engine off....you should get a reading of at least 13.2 for a good battery and a minimum of around 12.4 with a battery that's been standing for a couple of weeks.

Start engine, let warn up at idle and then test at the battery posts....you should be getting 13.8-14.5.
Get someone to rev engine to 2500rpm....you should be getting 14.8 maximum.
Allow to idle, then switch on A/C with blower fans maximum and headlights on high beam.
If you get a reading of less than 12.8, you have either a weak battery or below par charging circuit.
Below these figures, it's time to implement the 'Plums Plan' ;o)=)

 

Brian, check out this thread- https://www.jaguarforums.com/forum/x...esolved-84962/
One of the most common problems is the engine ground strap.

 

So very true Rob....and one of the most neglected.
Plum's point regarding di-electric grease is very interesting.

 

Thanks to all. I had seen that earlier thread but since I had some additional data I thought I'd start another.

I long ago stopped using dielectric grease anywhere that I wanted to ensure that my conductivity would be maximized. I've been using Sanchem No-Ox-Id A-special for some time now. Any time I touch an electrical connection I try to clean everything up and give it a good (but still light and thin) coating with No-Ox-Id before putting everything together. It keeps things looking as bright and shiny as when I first cleaned them for years and is electrically conductive as well.

Dielectric grease is great if you want to put a removable insulating coat on the outside of a connection to protect it, but conductive greases do this just as well provided you're not slopping them all over the place.

 

a flux brush is invaluable in applying the grease on the external surfaces.

most of the heavy power cables have a small hole on the nose of the wire portion of the ring terminal. presumably this is part of the manufacturing process. the hole should be filled with a small dab of either type of grease to prevent further internal corrosion

the same goes for the shrink wrap interfaces at the cable ends

now you see why it takes days

ps. the original cables are of excellent construction. if at all salvageable they are better than most replacements short of expensive custom made cabling

 

including the alternator bracket to engine block interface ... plus all four bolts?

 

By the way, although my grounding cable looked okay, it was no good at all. So cleaning up didn't help at all. A new cable fix the problem. Any decent size battery grounding cable is fine you don't need the special one.

 

I would agree with Plums about alternators or batteries or other electrical components being replaced needlessly on these cars when the problem was a simple connection that was not passing current as it should. My car acted very strangely as my ground cable gave out. It looked fine too. The crimp where the braid meets the cable end was not a good connection. A new battery ground cable took care of that for little money.

 

On mine, the ground strap got a conductive grease massage all over the braid.

The paint had to be removed at the grounding points at the body on both ground strap and battery ground cable. The conductive grease was then slathered generously over the connection.

As built, Jaguar seems to rely on the star washer and bolt or stud thread for contact. They do not remove the paint so that the flat surface of the ring terminal has a direct interface to the metal.

 

Well, just to finish my story and add another thing to check . . .

This afternoon I decided to begin cleaning out the car to prepare it for sale and to check things in and around the battery. I discovered that someone (and I will assure you that someone was not me) had not connected the negative cable from the battery to its ground stud quite tightly enough. It was clear that there had been occasional arcing at this point and it was evident on the cable connection (both sides) and the retaining nut. I am presuming this occurred when the new battery was installed, but I cannot be positive of that.

After cleaning both battery terminals, their line connectors, the crud off of the chassis end of the negative cable, and giving everything a thin coating of No-Ox-Id I started the car and am now getting a voltage reading of 14.09V at the battery.

While I was at it I cleaned up the connections that are on ground studs exactly like the one for the battery that are just fore and aft of same, along with their connectors.

Thanks again for the assistance. Having this fixed moves the car back into "I can sell with a good conscience" range.

 

Good find! Charging problems usually turn out to be something easily fixed like your issue.

 

On practically every make of car I have ever owned, this has always been the case ;o]
Have just finished doing my daighter's Hyundai and my wife's Peugeot for the very same reason.
Really perks up the systems once this is done ;o)

 

I'm glad you have finally nailed it. Brian...pity you now have to sell the car ;o]

 

Xjay8,

The sale is a combination of "have to" and "want to." When I bought this car, literally from a little old lady, she was selling it because she decided she no longer was able to drive in general and found getting into and out of this car in particular was difficult.

I've had the car nine years now and with knee and back issues creeping in am finding it difficult to get out of the car. My finances have also changed and I know that at its age and mileage (153K) I am going to continue to have some major repairs happening more routinely, and I'm not willing to spend more than the car is actually worth to keep it alive.

I am hoping that it will end up in the hands of a Jaguar loving person who has the time and money to love her as she deserves to be. This car is not a rust bucket nor an utter disaster, but is a 15 year old car that would need some TLC, mostly cosmetic TLC, to bring her back to her prime.