engine and drivetrain Anyone have a wiring schematic for an electric fuel pump?

[OH2DRV]

I'm not sure how you wire it up since you want it to turn off if the car dies or if you wreck so gas doesn't keep pumping...

It is my understanding that you need to tie into a circuit that is only on when the engine is running but also have a bypass for starting the car initially.

Any suggestions? Thanks

[Zenon]

To make the pump run only when the motor is running, you could ground the relay coil via the oil pressure switch. This would not run the pump until the oil pressure comes up, but on a carbed car this may not be such a big deal since the float bowls will usually be full enough to start the engine (the original mechanical pump is not doing that much during starting either).

Of course, it would still be nice to have a way to enable the pump to fill the carbs before you start - otherwise, if the bowl was empty, you would have to crank until the oil pressure comes up. You could do this with a manual pushbutton or perhaps another relay controlled by the starter solenoid trigger from the ignition switch.

So, you would supply power to one terminal (#85 on a Bosch relay) of the FP relay coil via any solid green wire (which on a 2002 is ignition-switched 12V that is on when in start and run positions but not in the acc position) and then ground the other relay coil teminal (#86) via the oil pressure switch. Just tap-in to the existing wire to the switch - the dash light will still work. The + power for the pump can come directly from the battery via a suitably fused 14 or 12 AWG wire to one of the normally-open relay contact terminals (#30) and proceed to the pump directly from the other (#87).

If you want to have a manual priming button, wire it between the relay coil terminal that goes to the oil pressure switch (#86) and ground (in addition to the connections described above, i.e. "across" the oil pressure switch). If you want an automatic prime, use a second relay controlled by the starter signal whose normally-open contacts complete the FP relay's ground as for the manual switch. There's probably a more clever and simple way to acheive the automatic pre-run pump action, but it escapes me at the moment.

For added safety you could also fit a shock-triggered cut-out switch. Many 80's-90's EFI Ford cars have these, usually in the trunk area. They are designed to break a circuit in case of an accident, especially a roll-over. I have not used one myself so no direct experience with wiring - you would probably just have it interrupt the power to the FP relay coil.

regards,

Zenon

[TimNC]

Thanks for taking the time to write this detail explanation. . . I too will soon be switching from the stock mechanical fuel pump to a Crane P4070 (as recommended by others here on the board) and had some of the same sort of questions you have just answered. Thanks again, Tim

[Mike Self]

Carbed '02s built after tii production began (1972 models) have a stray wire under the dash near the turn signal flasher box that's meant to power the tii electric fuel pump. It goes on and off with the ignition and is a good power source for your electric fuel pump. For safety, you could wire in an impact switch (magnetic reed or even a mercury switch) that would interrupt the current flow in an impact (magnetic reed switch) or if the car was tipped from its normal position (as in a rollover) (mercury switch). All you racers out there, what do you use to reliablly switch your electric fuel pump off in an accident?

mike

[OH2DRV]

I think that does make sense with the oil pressure, provided the float bowls haven't drained...it would just take some cranking. Good thinking.

I also found the extra wire on 72 (post tii introduction) for the fuel pump info quite interesting. I'll have to take a look on mine later. I have #2581446, I don't know where in the VINs it would start, but I'll look anyway.

[KFunk]

I'm not sure why you guys make this so complicated, theres a starter bypass on my Holley oil pressure switch. You run a wire from your starter solenoid up to post on the oil pressure switch (can't remember the name of that post). But when your starter is engaged, it bypasses the oil pressure switch function, and gives full power to the fuel pump while you're starting. The wiring diagram came with the switch.

http://store.summitracing.com/default.asp?target=partdetail.asp&autofilter=1∂=HLY-12-810&N=115+400178+300719&autoview=sku

Mine hasn't worked very well because I haven't had enough oil pressure to keep it on at idle. But I'm changing my oil pump now, and hopefully that fixes that.