If your xj8 will crank but will not start and throws the fuel pump code and trunk fuse box fuel pump relay code. Check to see if your front engine compartment ignition fuse, UHEGO,fuel pump, rear ignition relay coils fuse is HOT all the time. In my case it was fuse #1 and the fuse had no power. It should be hot. We discovered that the built in internal fuel pump relay failed in the front engine compartment fuse box and fuse #1 lost power . A jag mechanic had me install a jumper wire from fuse #2 (Throttle) to the dead #1 fuse This by passed the faulty built in fuel relay. My 06 xj8 started and has continued to run. About 2 years after this problem, my jag quit running all of a sudden. It would start immediately, run for 3 seconds and shut down. It again threw low fuel pressure, fuel pump codes. After checking fuses, relays, replacing the fuel filter and pulling and checking the fuel pump, I was checking the snorkel tube to the throttle body for cracks, I disconnected the mass air flow sensor and the car continued to run. I replaced the mass air flow sensor and the problem was solved. Recently, my check engine light came on but the car continued to run great. When I checked, it threw numerous codes. But the main codes were for the O2 sensors (low current). Again, another built in relay in the engine compartment fuse box that controls the O2 sensor heaters failed. Thanks to the forum and member 34by151 and his knowledge, we were able to install a 4 pronged external relay and follow his directions for wiring. I posted photos. You can find his Thread by entering his ID. 34by151 These may be temporary fixes. But they got me back on the road. In the process of replacing the front engine fuse box. It has already had 2 failures.

 

Here is the link to the fix
https://www.jaguarforums.com/forum/x...1/#post1897244

Post 7 and 10 for adding an external relay
Post 9 for replacing the relay

Cheers
34by151

 

I think that front box is prone to failure being in the harsh engine bay environment. Mine has intermittent issues with the air pump relay connection. Let us know how the replacement goes!

 

Amazing coincidence, I had the similar problem 6 months ago, had to have the car recovered into the dealer, they diagnosed the fusebox and I sourced a used one from ebay for about £60 instead of buying a new one. While they were at it they changed 3 earth studs and did a few other things for me as well