A 1990 XJ40 with a 3.2 engine?
What is the last six of the VIN on your car? If post VIN 529285 then it is a 1991 model (irespective of when it was first registered), the first year that they fitted the 3.2 litre AJ6 engine to the XJ40.
The model year is important - particularly in respect of the fuel system because in 1991 they fitted in-tank fuel pumps to replace the troublesome external pumps on the earlier models.
If you suspect a fuel problem, best to check the fuel pressure at the fuel rail - should be around 35 / 40 psi for the engine to run smoothly. http://www.jag-lovers.org/snaps/snap_view.php3?id=1357201999
This is the sort of kit you will need - http://www.jag-lovers.org/snaps/snap_view.php3?id=1076076938