86 Jaguar XJS V-12 convertible project


Power the relay with an external 12V source and see if it will operate the pump.
Check if the fuel pump relay gets the 12 signal from the ECU at the relay socket.
If not check the corresponding pin at the ECU plug.
If the ECU gives power to the relay then it’s either the realy or the wiring in between.
If not then the replacement ECU also has a problem.

Does the car start with the new ECU if you bypass the fuel pump relay?

One question you may be able to answer that I started another topic for. Could my buzzing ignition have anything to do with my fuel pump not operating when key is turned. Thanks

Maybe this has been suggested, but doesn’t buzzing means the lights have been left on? Could the light switch be faulty?

Jim 1984 XJSC Brighton UK

It could be in some cases but not this time. Makes sense to check though.

I can’t see a direct correlation between the buzzer and the fuel pump or ECU, but if the ignition switch is suspect and it could very well be that it’s not switching the main relay and ECU on?

I can see that a fuel pump that was seized might draw a high current and the fuel pump relay or ECU might a circuit that detects the high current and switches it off & this would cause the buzzing. Not very likely, but you could pull out the fuel pump relay and see if the buzzing goes away.

Jim Brighton UK XJSC 3.6 manual.

Nope… it’s still 80’s tech, no fancy gizmos.
ECU energises fuel pump via relay, so ECU has no idea if pump is seized or not.
More likely the pump will fry.