Hello,
I'm Jan Douglass proud owner of a new , to me, 2001 XJR purchased the end of July. It is titanium/oatmeal in amazing overall condition except, starting Wednesday of last week when I punch it, it really bogs down and runs like crap. I drove it from FL to PA and on my way back to FL I filled the tank with 87 octane gas and that's when it seemed to start. All of the cheap fuel is out of the tank now. I have filled it three more times with 93. I have tried it in all traction/sport combinations. Any ideas? Injector?

 

The first thing I would do is replace the fuel filter. You may have pumped some fuel with a lot of sediment, or maybe the tank had a lot of sediment to start with. The XJR has two fuel pumps, and the second opperates when you punch it. That pump may have failed.

 

Is that a fairly easy thing to replace?

 

With my 2001 XJR I read up on replacing my own filters seemed like a DIY project but filters were hard to get at and so I ended up buying the filters w/o-rings and having local Jiffy Lube center put them in place.
Cost of service $45.00 but well worth it .

 

You can test the 2 fuel pumps using a jumper wire from the battery to the pump relays in the trunk and listening to hear each fuel pump. There are multiple threads in this forum explaining how to connect the jumper.

If your car cranks for a long time before starting when cold this is a strong indicater that your secondary fuel pump is dead. The 2 pumps are in the fuel tank and require the fuel tank to be removed from the trunk to replace them.

As RJ suggested replacing the fuel filter is a good first step