I got a "Restricted Performance" warning light and limp mode on my XJR. My mechanic had his OBD on it and tells me it's the knock sensor (or perhaps he said NOx sensor? It was over the phone and hard to tell...). He said it's a pain to replace because the manifold and supercharger have to come off to get to it. Sounds like I'm in for a big labour bill... is this a problem that anyone else has had with thier XJR? Seems to me, we might as well refurb the supercharger as well whilst it's off (75k mile car). Any advice please?

 

It's the knock sensor (I don't remeber the car having a NOx sensor), and your mechanic is right, the manifold and supercharger have to come off.

As the car has two knock sensors, one for each bank of cylinders, I would replace both of them.

I don't hink the that the supercharger needs a refub at 75k miles. My SV8, that has the same engine as your car, meanwhile has double that figure without any refub of the supercharger.
If the supercharger blades are a nice black, which can be seen once the intake manifold has come off, it means that the coating is fine. If then the supercharger spins without any noise, I do not see any no need for a refub and I would just replace the supercharger oil while it is out of the car, it makes the job easier.

What is highly recommeded, instead, is that at the same time you replace the so called "valley hose", which is the cooling hose that runs between the cylinder banks underneath the supercharger.

There are numerous threads about the replacement of this hose, for example this one:
https://www.jaguarforums.com/forum/x...valley-134108/

In my case, it was the other way round: while doing the valley hose, I replaced the knock sensors, as well...

Best regards,

Thomas

 

Hello Thomas. I've passed your comments on to my mechanic Richard. and told him not to refurb the supercharger, but to do the 'Valley Hose' and other consumable gaskets, seals and pipes on the list instead. As always, your wisdom is much appreciated by this particular layman. My love affair with the car remains intact, however, my kids may now be disappointed at how little Santa leaves them this year! (But tough - I would sell them and their Mum on, before the car... )