Question about the fuel pump relay.

[adampecush]

I'm going to be wiring in a bosch relay in place of the stock toyota unit, while maintaining the stock resistor system. I have looked at the diagrams of aarons, and just wanted to confirm the stock system operation before wiring everything up.

at idle/low throttle, the stock relay is energized, connecting +B and PR (and hence including the fuel pump solenoid resistor)
under sufficient load, the relay is not energized, connecting +B and FP (giving the pump full voltage)

if this is incorrect let me know (as far as I know, it is though...)

 

[tlo86]

is your oem relay damaged or something?

 

[adampecush]

no, i'm wiring in a bosch-style relay to send +12V straight from the battery to the pump (bypassing the existing wiring)

 

[3p141592654]

As you state, relay energized for low-voltage.

 

[isnms]

You need 2 relays:
Fuel pump rewire diagram

 

[isnms]

no, i'm wiring in a bosch-style relay to send +12V straight from the battery to the pump (bypassing the existing wiring)

Was that helpful?

 

[adampecush]

yeah, the diagram was helpful. Is this the exact setup you used on your own car? I'm debating going with the straight +12V mod or the dual relay setup. Did you notice a more stable operation of the pump at idle? This is where my pump was having "issues" with producing sufficient pressure. Jumping +B and FP of course brought the pressure up.

 

[isnms]

Well... I haven't implemented it yet. I have not installed my mkiv pump yet.

It looks good on paper and jj says "Crude...but effective".

I have wired the relays and a resistor that I will try to get a picture of. I attached both relays to the resistor and they mount in the stock location. It could use some shorter wires and tidied up a little to keep the engine bay pristine.

[thumb]http://i80.photobucket.com/albums/j187/isnms/Supra/rewire_relays_fp.jpg[/thumb]

 

[3p141592654]

Adam, are you running a non-stock fuel pump?

 

[adampecush]

the standard walbro

 

[3p141592654]

What voltage do you measure at the pump terminals with the low-speed resistor enabled?

My thinking is that the stock pump draws less current and so the dropping resistor (0.7 ohms) is a little too big for the high volume pumps like the Walbro and the MKIV turbo pumps. The stock pump draws about 8 amps on low speed if I remember correctly.

Mouser.com and others sell 50W and bigger power resistors with lower resistance than the stock unit.