Hi there, been clipping along with trying to bring my newly acquired 84 XJS back to road worthiness but I have hit a new snag. My fuel pump does not prime with the key in the run position. The pump runs when the key is in the start position but then when the engine starts running and the key is back in run position the pump shuts off again. Pump runs and engine stays running when the orange ground wire on the fuel pump relay is jumpered to ground. I removed the electrical portion of the keyswitch and cleaned contacts (that sucked). Everything seems to be happening correctly, relays clicking and such but the problem remains. Any suggestions? Bought a used switch on e-bay but wondering if it will make any difference?

 

The fault is almost certainly the fuel pump circuit inside the ECU....that's the typical thing. Your jumping the orange wire to ground confirms it.

The ECU can be repaired or you can permanently leave the orange wire grounded. There's a safety issue in doing so but, if you did so, I'm sure you wouldn't be the first.

Or get a good used later ECU...the '16CU' type. I think these later version are not prone to the fuel circuit problem

Cheers
DD