For whatever reason the car seems hesitate on more than half throttle. There are no codes or lights just this issue with the car. If the car is given upto half throttle it runs great n has not hesitation. Give it some more and it feels like "restricted performance". Any ideas as to what it it...my thoughts are fuel filter or plugs.

Thanks in advance

 

A good place to start is to check the fuel pressure while at speed. There is a fuel pressure test port on the right side fuel header. Use a test guage with a long hose- tape the guage to the windshield (on the outside!) and make sure you have about 40 psi.
You did not say if you have an XJ8 or XJR. If you have a pressure problem on a XJR it is probably a failed second fuel pum. On the XJ8, I would look for a clogged inlet screen.

 

01 XJR is what I have. I was in the process of doing a maintenance on the car since ive only had it for 2 months and not sure if they mantained the car. If it is the pump...is it accessable thru the trunk and fairly easy to get to?

 

Q-
No, I am afraid it is inside the tank, and changing it requires removing the tank from the vehicle. The XJR has two pumps. There is a known wiring haerness problem as well as reports of a good many failed pumps. You might try checking the relay for the auxilliary pump. Check the archives for location.
I would test the pressur before I tore into the tank, though. Tank removal is a PITA because of te two push in hoses located under the car. I remove the rear boltsd and loosen the fron bolts on the subframe to get my fat hands in there, but others get the hoses loose without that. I beleieve I remember someone claiming to have gotten the pumps out without tank removal, by just displacing it some, but I would not do that due to the possiblity of crushing the fuel lines.

 

Well, if this fuel pump issue is the case I would assume its best to change out both of them while the tank is open and out...with the car having 83k? I wasnt really expecting this as I just got the stuff preped for the tranny fluid & filter change but might as well do it in one shot. I will check the fuel pressure on the rail as well.

By the way driving the car on the one pump...even though it runs without issues besides the full throttle has there been prior issues driving it like this?

 

Several folks have reported it. Some have claimed that it went on a long time before they realized a problem. I would fear potential serious engine problems due to lean burn as the pressure drops, although I do not remember anyone claiming that happened. The wiring harness also has a problem, which I am niot personally familiar with. Mine were OK. Maybe someone with knowledge of the inside the tank wiring connector can chime in.