I just did 1500+ miles in the XKR in Scotland but it was plagued with "Restricted Performance" messages every now and then. Caused by I think two problems the throttle body and the water coolant temperature sensor. I replaced the sensor the year before because it was playing up then and now I think this one is playing up. It would read that the coolant temp is too high and put the car into restricted performance mode but if you turned the car off and on again it would go away. I checked the actual coolant temp with an OBDII reader and it was at 75C so there isn't anything wrong with the cooling system there I'm pretty sure it's just the sensor. With the throttle body I would fix it by taking the intake off and giving the area around the butterfly valve a good clean out and it would go away for a while and come back again. I'm not sure how to get rid of this problem permanently does anyone know a way and also am I just unlucky coolant sensors or is there a better way to fix it then to keep buying new sensors? It's a 2003 4.2 XKR.

 

how old is your battery ?

It’s likely beating the old dead horse, but try a
load test on your battery or a new battery outright . These cars are exceedingly demanding when it come to having a battery in tip top shape.

many electrical faults on these cars are solved by a new battery, although seemingly there’s nothing wrong with the old one.

also, if not already being done, out the battery on a battery tender whenever the car is not being used overnight or longer. Besides extending battery life, doing this keeps many electrical gremlins away.

Z

 

The battery is brand new repalced last year by me. I also had a "gearbox fault" message on the dash at one point during the trip but it was fixed by turning off the engine and on again. Never came on again. To be fair I was using the J gate a lot and revving the engine out a lot up hills which probably isn't good. I've had it come up in the past as well but it's always gone easily. Never left any codes in the ODBII which is odd. Oil change was done at 60k miles which was only 10k miles ago so that shouldn't be a problem.

 

''Brand new last year'' is not new.

ln my experience anytime my battery drops below 85% from sitting it will throw random codes, ABS - TRAC, TRANS on the dash and also never leave codes on my ''mere mortal'' ODB reader to the point were i plug the trickle charger in every time i get home, not a code since. These are as voltage sensitive car as ive ever come across, to the point were i will change the battery at 2 years. lf i where you i would change the battery.

 

Will look at it but batteries aren't cheap to replace every year.

 

..............................neither are 1000 mile bimbles around Scotland, its all about priorities i guess.

 

Very true but one is fun the other isn't. Think I spent about £350 on fuel. For my yearly holiday that isn't bad.

 

In consideration of your damp climate it would be a good idea to remove and clean the connections of the engine to chassis ground at the right rear of the engine and both battery cables.
If you are able to use a battery maintainer, such as a CTEK that would extend the life of the battery.
A generic code reader will not read the transmission codes.

 

I will give that a shot. I will also check my fuses to make sure they are OK.

Edit: I could only find my engine block ground and that looks a bit green so I suppose that could be the problem. My battery contacts and fuses all look good though at least the ones I could find. I couldn't find the very front ground point and not the transmission ground either. I suppose I will have to get the car jacked up to find them? I might see if I can clean all my connectors and see if that helps or I've read there is a large connector under the car that goes into the transmission.

 

The 6HP26 transmission does have a problem with fluid getting into the cable and causing trouble, so not a bad idea to replace the sleeve. I don't think there is a transmission ground, just the strap from the bell housing to the frame accessed from underneath on the right side.

 

Ah cool. I was looking for another one. I found the engine one and it's a bit green in colour so I will probably have that looked atwhen it's more easily accessible. I will probably have to find someone who can do a full service on the transmission. Do a full oil change and get the rubber sleave seals replaced and the cable sleeve.

 

When was the last time you cleaned the MAFS?

 

I never have, the previous owners may have though. Might look at doing that as well.

 

One of the things that get overlooked on these are the fuel filters and MAFS. My craiglist cat ('01 XK8) was original fuel filter, and air could barely go through it. @rothwell Happened to drop by one day with and extra Fuel Filter he happened to have.... When does that ever happen?! . That and the MAFS was dirty as all get out. Threw restricted performance codes anytime I tried to rev over 3k.

Get the real CRC MAFS cleaner and clean BOTH wires good JUST WITH SPRAY. Don't touch it with anything.

Gus has great info here:

MAFS Reading

MAFS Cleaning

 

I have bookmarked those readings and will look at that tomorrow when the sun rises. Not sure if my OBDII can read the MAFS readings but I will have a look. It can read the fuel trim and all that stuff so I guess it should.

 

It's a good start to check, but I'm going to start adding the MAFS cleaning to my "yearly" once over checklist. Easy to do, just spray it good and let it dry. Put back in. I didn't even get sweaty.

 

It sounds like the problem I had with my 2000 XK8. I ended up sending the throttle body out to be remanufactured and haven't had a problem since, until my ca was run into by a careless driver.
That is another story.

 

Is there anyone in the UK that can rebuild them? I've seen a place that can do the 4.0 throttle body but they don't list the 4.2.

 

I took some readings this morning. My 900 rpm is at around 11 g/s, 800 about 9.4 g/s, 2500rpm 25 g/s and 700rpm about 7.6 g/s. So I think my MAFS will need cleaning. I took some other stats to see if they where OK as well. Short term fuel trim bank 1 is at about -4.7%, long term is at 3.1%, bank 2 short is at 0.0% and long term is at -0.8%. Intake timing advance is at 7.0-6.0 degrees on 1cylinder? Fuel rail pressure is around 380kpa and intake manifold pressure is at 38kpa.

I bought some MAFS cleaner and throttle body cleaner so I can give it all a good clean. Just have to wait for it to come down.

 

Replace the MAF sensor plug, it gets loose and doesn't make good connections anymore. I did this on my 2002 xk8 and had no more problems!