Okay, So i'm driving, and suddenly when I start to pull out from a stop light I have pretty much no power, and I had to floor it just to get up to speed. Plus the check engine light popped on (thanks jag...) So when I got home I popped the hood and looked in, on side of my exhaust was cherry red around the cat. I quick turned the car off and checked the VCM, it said fuel fail 44. With some looking around it said that it was my O2 sensor. Now, with some more looking around, I found some XJ-S info saying something about the Marelli ignition making them run on 6 cylinders instead of 12. I dont know if my car has the Marelli, but that said all the symptoms (no power, rough idle, glowing red exhaust) seem to indicate that is it. That said, I dont know how to fix that, and I have had no luck finding the information on how to do so. If that is even the issue, I dont know. Any one on here have the same issue or know what is the matter, any information would be greatly appreciated!

 

Your frame is like the rest of the XJ40's in this section of the forum, your engine is a whole different beast. Your answers to your engine issues can be found in the XJS section.
With that said, and I owning the same v12 as you, but in an xjs, advise you not to drive your car or it will, and I repeat, it will catch on fire. You got away with this one, next time maybe not. Your car has 2 ignition coils, when one fails it will run on 6 cycl while unburnt fuel finds its way to those cats, which will start a fire. I know because it happened to me.
The coil needs replacing. My advise to you is to go to the XJS section and read the 800 page V12 book that is available there so you can get to know your engine. The beginning of the book explains the ignition fail fire issue. And if you are sweating the mechanics involved in changing the coil, or don't even know where it is, you better have a treasure chest buried somewhere, because it's going to cost $$$ to keep up with that engine if you are incapable of doing it yourself.

I don't want to discourage you, and have you get turned off by a jag, its just that the v12 isn't the most gentlest approach to owning your first one.

I owned 3 XJ6's for a few years prior to getting the XJS.

If you still want to have at it, visit the XJS section, if it wasn't for those members in there I wouldn't have bought one, they know their stuff over there.

Oh, and always keep a fire extinguisher in your car.