Fuel Pump Relay Switched Earth

[Ryan.G]

Hi Guys

 

Need abit of help, Basically wiring in a link ecu on a auto supra and trying to figure out which pin is the switch earth for the fuel pump relay.

 

Have looked at the voltage signals and the FPC and DI are both not switched earth. They both supply power. From what i can see FPC is the pulse that tell the fuel pump ecu to change from 9v to 12v and then DI looks like its a switch live. But on most car i have wired in the link they have switched earth so just wondering if the supra does not use a switched earth and sends 12v to switch the relay.

 

[Supra ST Myster]

when i made the 12V fuel pump method, there is a pin that switches to 12V as thats the pin that you tap onto to give it the 12V rather than 9V all the time when ignition is on.

[SimonB]

There is no fuel pump relay as such. There is the fuel pump ECU, which as you have found has FPC which the ECU pulses to send 9V or 12V down and DI which is the diagnostics line back to the ECU. It also has a 12V thicker gauge power cable which goes to the EFI main relay. So to turn the fuel pump on the ECU activates the main EFI relay (which in turn switches the EFI 2 relay) to supply power, then switches FPC to tell the fuel pump ECU to send that power to the fuel pump.

 

My Motec is wired up so the fuel pump relay output on the Motec switches the EFI main relay on, and the fuel pump ECU is bypassed by connecting the main 12V feed to the fuel pump direct. At least it was that way, now I have 2 pumps I have a couple of relays that are switched from the 12V feed and a 40A cable direct to the battery.

 

The wiring diagrams are on mkiv.com but it doesn't seem to be working atm.

[Ryan.G]

Thanks for your reply simon this was the answer i was looking for

 

Good man

 

Ryan