Hey Lads,

This is a cautionary tale for those that are having issues with their XJ6 similar to mine.

You can find a number of threads on the forum relating to issues I was having including:

Temp Gauge Pegging -
Lumpy Idle -
A dip in idle every 32 seconds -

This all started on one single day when my son was following me in the Jag to drop off my RV for service. When we got to the business, he said the temp needle was pegged in the car. It's Vegas so I take any temperature related issue seriously. When I started the car, the needle was at normal so I asked what was up? Within about 30 seconds, the needle pegged again so I was sure we were overheating even though the car didn't seem hot? I even opened the overflow tank and touched the coolant in there and it wasn't even hot, just warm. The car was also started stalling and causing some major grief. If I restarted it, it would start fine and the temp gauge would go back to normal for a minute or so and then would peg again. It would also run ok for a few minutes and then start to stumble really badly. These are things I feared were related to the car overheating and it sent me down a path of investigation that took a long time to finally rectify.

The car was bought as a restoration and I got it for a song due to it not running. The starter would not even engage so the owner just wanted it gone. It didn't take much investigation to discover that the issue was the ground strap between the chassis and the engine which lives on the drivers side down by the starter motor. After cleaning this up, the car started and ran perfectly. But that was then!

So over the last months (I travel a lot I replaced a number of parts dealing with two specific issues, one being the constantly pegging temp needle and the other being a poor, lumpy, idle. I didn't invest a ton of money but some of the things I replaced were the fuel pressure regulator, had the fuel injectors cleaned and flowed, replaced the CTS and even installed an aftermarket temp gauge which also showed the car running in the 220F range. I also recently replaced the thermostat and the overflow cap which was definitely shot. The car seemed better but the temp needle still shot to hot and the idle was still not as smooth as it used to be. This forum helped me immensely and patiently as I jumped from one possible solution to another but nothing truly "fixed" the problems.

There was one other thing that was happening too and that was the battery needed constant recharging. I would charge it up and the car would start fine but after a couple of days, the starting would be sluggish and I would charge it again, I thought it may be the battery going bad or maybe a parasitic drain was happening - great, another issue.

So just by chance, I noticed something the other day after I had replaced the overflow cap and was taking it out for a test drive. When the needle pegged as it always does for temp, I noticed that my voltage gauge was below the 13V middle. When I got back to the house, I turned the car off, checked to see that my new cap was making pressure and then I restarted the car again. The temp needle went to the middle and the voltage needle went to about 14V. I let the car sit and run for about 20 minutes and neither needle moved.

I should also mention that every single test I did with temperature confirmed that the car was NOT overheating but was in fact running around 185-195F at full soak. The car itself was saying otherwise but I trusted my external meter and temp gun which were in agreement with each other.

So I put all the pieces of the puzzle together and said to myself "You know what, even though you cleaned that ground strap, let's do it again and see what happens". So I jacked up the car and pulled the strap right off of there. Wire-wheeled the terminals and used some sandpaper to clean up the contact surfaces on the chassis and the engine. I used some dielectric grease on the terminals and torqued the bolts down good and tight. I really didn't have much hope for this but dropped the car off the jackstands and fired it up.

The voltage meter went to 14V and after a minute or two the temp needle went to just below N which is where it always sat. The idle seemed very stable with just a very small wobble on the engine which I consider very normal on a car with nearly 180,000 miles on the clock. I let the car run for an hour and the temp needle never moved and neither did the voltage. The 32 second dip in idle is completely gone and the car starts with authority every time.

So after dancing around with dozens of possible scenarios, it looks like the ground strap was the culprit all along even though I had already cleaned that before? The really odd thing is that I live in Vegas which is a really dry area so it baffles me that this was an issue to begin with? I would suspect it more in cold, wet climates where corrosion is a factor.

So before I call it completely fixed I am going to drive the car for a day or two and see if any of the original symptoms return but given the rather drastic change in everything, I think its licked.

This is a cautionary tale for those having any issues similar to mine or any type of rough idle, poor starting or mystery meters on the dash. Do yourself a favor before you start slinging parts at it and remove and thoroughly clean that ground strap and connection points for it. It very well may be the issue you are having too! I am going to go one step further and add an additional strap somewhere else in the engine compartment just to insure that the ground is always secure.

So relieved that it is finally resolved and I can move on to replacing all the bushings and balljoints for the front end. I have been putting that off until I resolved these running issues. Again, thanks to everyone who rallied around me on this issue.

Bernie

 

Well done.

I have mentioned that earth strap/s for as long as I can remember, as sorting that little sucker usually solves so many issues.

We V12 guys know all about earth strap failures.

 

Given the many issues that can arise on these cars from a ground strap problem, I think it is the best place to start before looking at replacing any parts.

Another simple test is to use a set of jumper cables in the engine bay to create a temporary ground to see if any of the issues clean up. Obviously you don't want to drive the car this way but it can help to quickly identify if a grounding issue is causing your problems.

Bernie

 

Are there any opportunities to add other grounding straps/locations to the engine and frame?

One doesn't want to go wild doing so, but I've seen that advice for other auto and motorcycle makes/models to solve poor grounding problems.

.

 

Al,

There are plenty. I usually look around under the car when I change the oil, and find a suitable sump bolt, and a chassis bolt nearby, and fit said strap whilst waiting for the oil to drain.

 

posting of picture of the straps would help those who are novice.

 

bump

 

I'm putting mine on the lift tomorrow to take a look, but a reference pic would be nice beforehand.

 

For the guys interested. I cleaned mine up today. It was a bit greasy and nasty on the chassis side. I'll report back with results once I drive it a bit.

 

Thanks a bunch man. Appreciate it.

 

Just want to make sure that you guys know you need to remove it and clean the terminals and the mounting areas.

I used some medium grit sandpaper to clean off the terminals and the spot on the starter and spot on the chassis where it mounts.

I then used a bit of di-electric grease to coat everything to keep moisture off the areas. Tighten the bolts down good. Not breaker bar tight but tight.

Easy job that shouldn't take more than 30 minutes to complete.

Bernie

 

After driving around a bit, it seems cleaning the ground didn't solve my particular issue.

 

Remember that dielectric grease is an insulator, not a conductor. So if one puts dielectric grease on the surfaces that need to compete a circuit, you are impeding the connection.

.

 

I have used dielectric on connections for years and years. On battery posts, chassis connections and even on bulbs. Never had an issue. It has very low film strength and keeps moisture off the parts.

So get this,
I had to tighten the strap down for the third time! Yes you read that right.
The gauges went funny again and when I got underneath to check it was loose on the starter side ------------------- again!

I suspect that the vibration and torque of the starter might be causing it to loosen off. So this time I went with blue loctite and also a star washer just to make sure it doesn't happen again.

The difference this time is that the problem I thought I was having with my starter has now been fixed with the strap issue again. LMAO

 

I add an extra strap or 2 wherever is convenient.

Doing the 2 S Types over this holiday weekend, coz I believe it is a preventative thing.

 

Is it possible that the lubrication of the dielectric grease is interfering with the friction the ground strap screw needs to remain tight, allowing it to vibrate loose?

Dielectric grease is generally fine on high-power connections, but given how sensitive Jaguar electricals and electronics are, I've adopted the practice of securing connections clean and dry, then covering the exposed terminals and screws with dielectric grease only after everything is tight.

And I never use dielectric grease on the contacts of low-power circuits such as those for sensors and such. I just apply a little grease to the outside of the inner half of a plastic connector to help prevent oil or water from contaminating the connector.

My two cents....

Cheers,

Don

 

I guess it is possible but that wouldn't explain it the first two times when I didn't use any grease at all. When I purchased the car it wouldn't even turn over the starter - engine strap. When I fixed that it worked for a while and then we started having the problems with the gauges and the poor idle - engine strap. Then I started having starter issues again and then the gauges went funky again - engine strap...........lol.

I only used it the third time when I did some serious cleanup of the connection points. Certainly, with a star washer and loctite, it is not going to find its way loose again and if it does, I will be looking for a reason other than the obvious.