Fuel pump always on

[AndyP]

I connected the battery today after an extensive engine re-build and found that the fuel pump is always running, even with no key in the car!

I have a second fuel pump relay under the rear seat which is switched using the green/yellow wire that originally drove the pump and this seems to be live all the time. I've checked the original J17 pump relay and the G28 engine speed sensor, both seem to be working normally, but the pump still runs, even with both of these unplugged.

I know the ECU looks for 13rpm from the G28 before switching on the pump, so what could be broken on mine that making the pump live all the time??

[S2central.net]

Could be sticky contacts on the relay itself preventing them from opening - or someone has bodged some wiring to activate them regardless of control signal from ECU ?
Heck if the pump runs when J17 relay is unplugged then someone must have wired the pump up directly to bypass that !

[AndyP]

Apart from re-locating the battery to under the rear seat, nothing has been changed electrically from how it was running before, and it worked fine.

I'm going to have to trace that yellow/green wire and see where it's getting power from. I presume it should go to one of the pins on J17

[DJones]

Andy, whilest I can't remember the colour of the wire, the trigger from the ECU is earth. I.e. A switched earth.

Darren.

[rj scotty]

Andy, whilest I can't remember the colour of the wire, the trigger from the ECU is earth. I.e. A switched earth.

Darren.

This is true.

Live side of the fuel pump relay coil is fed from an ignition switched live, negative side is pulled to ground when he ecu detects that the engine is rotating.

[S2central.net]

Yes its a brown/green wire usually that connects to control side of J17 from ECU... if it is getting shorted to ground that would activate pump when key is ON.
But the behaviour described here suggests a short to 12V onto the green/yellow wire that powers the fuel pump - could it be rubbing through under rear seat after that battery relocation work ????

[AndyP]

Thanks for all the usefull info, I'll have a poke around with the multi-meter tomorrow and see what I can find

[S2central.net]

Meantime I sincerely hope the battery is disconnected (cough) !