Sorry about the brevity of the previous answer! It was getting late at night for me! This particular figure came from JTIS - the Jaguar issued 'Jaguar Technical (Some say Technician!) Information System'. Google it for endless information about it! I find it an indispensible source of info for myself and to pass on to others who may not wish to become too involved in technical publications.
A number of things can cause low fuel pressure - failing pump (Two in XKRs), dodgy pressure regulator or, a good start point, a blocked fuel filter. That's where I'd begin.
Sorry for being a further pain but you couldn't tell me where in the JTIS (Have looked in fuel sytems and charging to no avail).
The pump has been out once before and I am fairly sure I have not re-assembled it properly.
I agree, JTIS can be a pain when trying to locate some details! In my version, the info you need is under Powertrain-Fuel System, General Information-Specifications. It gives Tank Capacity -75 liters(sic!), System Pressure, supercharged - 5.0 bar, not supercharged - 3.8 bar.
If I press the 'New' icon, it says JTIS Release 21. It covers the XK range to MY2004.00. Fuel Charging and Controls is Section 303-04, but Fuel System, General Information is further down the Powertrain Menu at Section 310-00
Thankyou Astro for those detailed instructions I have now found the left hand numbered column with 310 etc (Version 17 in use) and can confirm to have the same recommended fuel bar pressure as you mention and the same pump is fitted to the car as the one described in Version 17.
A furtherence: this pump has been removed before due to poor running and was found to have broken clips allowing the ball valve and spring to escape to the bottom of the tank. It is now thought that the ball has been put the wrong end of the spring.
I'll post some pictures and hopefully someone with better knowledge can advise.
Thankyou for your help.
To support the installation of the 4.2-liter engines and continuing the drive for fuel
consumption benefits, a new fuel system including fuel tank, fuel pump, pipes, breather
pipes has been installed.
The XK now benefits from the use of the return-less fuel delivery system very similar to the
X-Type and S-TYPE models.
One major change on supercharged (S/C) variants is the use of only one fuel pump instead
of the usual two as used on all previous S/C models (XJR, XKR and S-TYPE R).
The fuel pump uses the same principle of operation as the on the X-TYPE where the ECM
monitors differential pressure across the fuel injectors and the injector pulse width and
duration to accurately calculate the fuel quantity being delivered to the cylinders. It uses
this to demand a specific fuel flow rate, which it communicates to a fuel pump driver
module located in the right hand side rear wheel arch.