Hi guys,
I'm only new to this forum, but love the great information and help everybody has provided.

My XJR is having a issue when I overtake. It kicks down and continues to pull hard but it refuses to change back up until i'm back down to about 80km/h. The traction and stability control lights come on as well as the abs, and if i have my lights on the headlights flicker and blow.
I have had the battery checked by 5 different places and it is 85% at 900 crank amps, the codes that I have pulled off it related to LHF sensor, and high temp gearbox sensor. Which stops me having a little fun, I have also taken it to a number of auto electricians where one informed me that my dash was blinking when this happens??
Any advice would be greatly appreciated. Sorry for the long first post.

 

Welcome to the forum Kascol,

I've moved your question from New Member Area - Intro a MUST to X308 forum.

Members here with the same model will be able to help.

Graham

 

Thank you Graham, and nice xk

 

So, if the battery is good and the "headlights fliker and blow" it sounds like you have an overvoltage condition from the alternator OR a wiring problem from the alternator to the battery. That would include the "false bulkhead" connectors near the firewall- the big power connectors for the big black wires. Check the archives for more info, but you are looking to see if those connectors are not corroded, and to make sure they are tight. I would also have a look at the battery and engine ground straps.

The "blown light" description was not very specific but I believe it is the key differentiation to determine your root cause. If it is not the root cause of the other problems, it sure as hell needs to be fixed anyway!

 

I don't think he meant his headlights actually blew out, Ross, maybe just flicker and get brighter ? In any event, I would second the possibility of a grounding problem. I've had it before, not the same issue, but related to grounds. I replaced all the braided cables with heavy solid ones. Maybe that's ****, but I spent a lot of time worrying and wondering if it wasn't some major problem.

 

You may try replacing the battery anyway, that sounds EXACTLY like what mine was doing right before the battery failed as the voltage got lower. It's also right before my alternator failed, which might have had something to do with it. Get your alternator checked as well.

 

Thanks guys,
I will have a look at the earthing this weekend. It blew one bulb two days ago, so i replaced both and then it blew both last night during overtaking lucky for fog lamps.
Checked the alternator and is charging at 14v, battery after a half hour trip is sitting on 12.4v. Will be checking it tomorrow morning after sitting overnight.
Just asking, as i am not up to speed yet with all this electrical stuff on the jags, would this problem cause the car not to change up a gear?

 

I recommend you get your alternator tested for overvoltage QUICK before you blow something besides bulbs!

 

Will do, thanks Ross

 

Look in my signature, there's a link to a step by step procedure to go through the electrical systems and possible issues. Report back and let us know what you find.

Good luck!

 

On the Merc transmission in the XJR, there is an electrical connector at the right front corner of the transmission. It is common for the seal to leak. When this happens transmission fluid wicks up the harness amongst other things. This has the potential to be the source of the problem if the harness is shorting out.

The sleeve is cheap to replace. Get one from a Merc dealer because they carry the new improved design.

 

Hi guys,
Thank you for all your advice regarding my problem.
I have checked the voltage from the battery, alternator, false fire wall and the connection where near the battery where the power meets prior to going to the rest of the car. All read about the 14.2v.
I have the car booked with an auto electrician for Friday where we will plug in the reader and go for a drive to see real time what is going on. Didn't get to crawl under the car for checking earth leads will get to this, this week.
Will let you know how I get on.

 

I changed my alternator on Friday and I had changed the alternator on my other XJR two years prior and this is not fun . If you have access to a lift I highly recommend it It can come out the top yes but you have to take a lot more off...

 

May be time to find the common power supply to all the problems - do they all come from the same fuse box, do they share a common earth
Cheers
DC

 

Will have to look into that.
Thanks DC

 

Hi guys,

Just thought i would let you know how things are progressing. Well i took the auto electrician for a ride and the only thing we found was that when the problem happened there was a spike in the electricals, no codes just a spike. So after returning to his shop we tried a few different things and found a voltage drop of 1/2 a volt from chassy to engine and under load at the false firewall without engine running at 800 crank amps we had a voltage of about 10v. I have changed the engine earth lead and will be getting a new battery soon, i have also cleaned my front speed sensors.
Everything under the car is spotless with no oil leaks, but i did notice a lead coming out of the front of my gearbox ( centre) which was a little sus. Think it might be speed sensor imput, not sure.
Thanks again for all your help and i will see how it goes over the next couple of weeks.

 

Clean your earth leads and engine ground and starter ground. Make sure you have correct voltage during running. Take the car to napa for a free battery analysis. A healthy correct size battery should have a thousands amps. If the alternator is bad in the x308 you will get "ghost" check engine lights. most recently I had a ABS/Traction control failure even the scan tool said it was the problem. I knew better and big surprise/not really the ABS/traction failure is gone.

 

Hi guys,
Just wanted to let everyone who helped me.
I changed my battery and also found an earth lead (loose) attached to the bonnet hinge (now tight).
This seems to have fixed a lot of the problems- now just have to clear the codes and service. Hope this will stop the little bit of surging and allow her to rev a little easier.
Will also be changing plugs, and fuel filter.
Again I just wanted to thank everybody for all your assistance.
KK

 

Thanks for posting the fix. Always good to have a conclusion and it could help others troubleshoot the same symptoms in future.

Graham