Hey Guest!
Hello Tino
Welcome to the forum.
You should try posting in the Jaguar section of the forum. I am sure someone there will be able to help with your Hot Cat.
Post some photos of your XJ v12
David
Was about to post the same about the gas being sent into the exhaust unburnt and eventually burning in the cat.
David
Look farther down the listings until you see Jaguar, and we'll see if we can talk you thru the diagnostics. Not a hard car to figure, but a lot of work to get there. Whatever you do, do not continually get the cats red hot.