Fuel Pump Direct Feed Rewire.

[heller44]

Not really sure; from what I can see its pretty straight forward whats going on.

When the FPCM receives the signal from the ECU the the voltage earths directly.

When the FPCM doesn't receive the signal from the ecu the earth passes through the dropping resistor.

The GTR is essentially identical apart from the FPCM containing the dropping resistor and receiving 2 signals from the ecu to determine if the fuel pump is high or low.

The voltage reduction isn't an issue, thats easy to understand, more that I was just wondering what the 'air regulator' that is on the load side of the fuel pump relay actually did.

[Cubes]

The air regulator has nothing to do with the fuel pump control.

Ignore the big arsed diagram as it can be misleading.

[wlspn]

I am sorry to hijack your thread but it seemed easier than starting a new one. I have an r32 GTST with some mild mods (hi-flow,etc). I am wondering, is there any advantage in re-wiring the stock pump like this? & can I just earth out a wire rather than replace everything. If so, which wire? I am just after a slight increase until I fit a new pump. Am going to go & check voltages now. Will post them up when found

[Cubes]

The problem is the + feed; earthing to the chassis does increase voltage slightly but when the pump is working hard against high fuel pressure (base pressure + boost pressure) voltage drops as the std wiring cannot handle the current draw.

[B0oStEr]

Not really sure; from what I can see its pretty straight forward whats going on.

When the FPCM receives the signal from the ECU the the voltage earths directly.

When the FPCM doesn't receive the signal from the ecu the earth passes through the dropping resistor.

The GTR is essentially identical apart from the FPCM containing the dropping resistor and receiving 2 signals from the ecu to determine if the fuel pump is high or low.

Does anyone know whether ecu pin 104 earths or gives a 12v trigger to switch the fpcm to direct earth?

[heller44]

According to the service manual, at idle (after warm up) 0v, at 2500rpm during middle load 4v. This is for 104.

Active high i take it to mean.

james.

[robots]

Can anyone post some pics or a diagram of their fuel pump feed/ground rewired ?

Thanks!

[GeeTR]

Pics of what specifically?

[Duncan]

this is the autocad diagram we used to plan the install:

[robots]

Pics of the wiring job/relays etc.

Damn, this diagram is tough ))) Got to check if my setup looks similar to the diagram lol

[dmac_25]

From what i have read and understood is that the standard 12v turns the relay on so the constant 12v from the battery flows to the pump.

Also i had an amp in my boot at on stage and the wires are still there just not hooked up to the battery could i use that wire i carnt remember what gage it is but is pretty big.

Cheers

[Oosh]

Other than weight there's not really any downsides to using overkill sized wire.

Why not use something a little more sensibly sized and used to the existing chunky wire as your draw cable?

i.e. Tape the new wire to old, and pull it thru.

[B0oStEr]

I had a bit of time on my hands this week.

I swapped my r32 gtst pump over to a r32 gtr pump and decided to do the wiring upgrade.

After reading this thread through I used the schematic from the thread and traced all the fuel system wires in the car with a multi meter and found the fuel pump control modulator and factory relay in the boot. I also located the dropping resistor for the low speed in the enginebay.

This process has shown me how the system works but there is one thing about the system I still don't understand.

The black/yellow wire that is the power from the factory relay to the fuel pump and also supplies power to the fpcm but then for some reason runs back into the loom toward the front of the car.

The schematic doesn't show this.

What does it do?

Has anyone got an actual wiring diagram?

[_x_FiReStOrM_x_]

Just wondering if this mod poses any safey concerns relating to the fuel pump safety shut off (ie, event of an accident)? Or is it totally unrelated?

Cheers.

[Cubes]

Providing you use the original wiring to trigger the relay it poses no problem.

[B0oStEr]

Just wondering if this mod poses any safey concerns relating to the fuel pump safety shut off (ie, event of an accident)? Or is it totally unrelated?

It does actually bypass one safeguard.

The power to the factory relay is switched by ignition so even if the relay fails and locks on the pump will only run when the ignition is on.

With this mod if the relay locks on the pump will run regardless of whether the ignition is on or off.

[Cubes]

It does actually bypass one safeguard.

The power to the factory relay is switched by ignition so even if the relay fails and locks on the pump will only run when the ignition is on.

With this mod if the relay locks on the pump will run regardless of whether the ignition is on or off.

Easy fixed... run another relay that is activated by the ignition switch. As per factory.

[Duncan]

or one of those oil pressure switches that cut the fuel pump as soon as the oil pressure goes

[Cubes]

I'm really not worried about it.

With the factory setup...

Your in an accident and for what ever reason the factory relay fails the system will still run until you kill the ignition.

If the factory relay were to take a hit and some how weld on chances are it would short the wires attached so its unlikely the fuel pump would run.

If the relay were to weld on under normal conditions; you turn the car off WTF the fuel pump is still running. Some things not right with that I'd better fix it.

I believe its unlikely to become a problem. Sure it doesn't meet ADR's but hell it doesn't anyway nor does that bigger turbo or rb30 sitting under the hood. :S

[mtopxsecret6]

well.. i did the mod on my car today, but i re wired it all the way to the fuel pump itself. but i t still didnt fix my problem. Though.. i did notice my injector duty cycle did increase dramatically after doing this mod.