How high does your XJR rev?
#21
#22
With the car off, you can jump each fuel pump individually, by pulling the relay and jumping the two correct pins (the center one and the perpendicular one) and listening for the pumps. If a pump doesn't run when the secondary pump relay is jumped, then you know that that is at least part of the problem. If each pump runs, then you can go onto more involved tests. Also worth checking for kinked fuel lines in case the previous owner didn't do so good a job with them...
#23