Can you slow down a fuel pump? - Opposite of boost a pump
 

Hay guys,

I know that you can get booster for fuel pumps to increase their rating, but is it possible to do anything to the wireing of an external pump to get it to flow LESS fuel?

Reason I ask is I am helping my brother out with an engine swap (admittidly, its not a rotary, or an RX7 for that matter). We have put a 4AGE in his KE35 carolla. The fuel system is a lift pump, surge tank and 500hp feel pump. Factory 4AGE FPR.

This feel pump is way too big for the little NA 1600 but its all we have to work with and he has no money for a reg.

The factory fuel regulator cannot return enough fuel, resulting in a really rich car at anything other then WOT.

So is there anyway to include resisters or somehting in the wireing to slow the pump down and flow less fuel?

you could run a restrictive return line back to the tank from before the regulator but thats some macgyver shit. or you could trade pumps with someone with something smaller. I have a s5 na pump :)

A note on using resistors - your pump probably pulls around 7 or 8 amps at 12 volts and 40psi. You will end up with very large wattage resistors which are not exactly cheap.

The problem I have is finding a small external pump thats not gonna cost mega bucks.

I have managed to find an external BMW pump at a wreckers, but I tried that last night and it was seized :(

All the external pumps are 500hp+ raited ones over here so Im a bit stuck.

Looks like it might be a new FPR and fittings to connect the dots. :icon_no2:

Try using a factory S4 T2 fuel pump resistor/relay box. A lot of people cut them out anyway.

https://www.rx7club.com/attachment.p...1&d=1255650011

you can see in this circuit diagram that, from the factory, the resistor relay is supplied voltage from the circuit opening relay through a lightblue/red wire. The wire branches off into two sections. With the resistor relay off (coil disengaged such as at idle), it passes through the resistor inside the box and comes out one of the light blue wires. When the ECU wants to run the pump in high speed mode, the coil in the relay is engaged by a ground supplied by the Green/Red wire. The current now passes through the path of least resistance, through the other matching pair of light blue/red and light blue wires.

Because the wires are two pairs (light blue/red and light blue) of the same colors, you would want to check for resistance across each pair to determine which wires to use. One pair (the two wires you want to use) should have some decent level of resistance because it passes through the internal resistor. I believe the other should be open circuit unless you trigger the relay by supplying power and ground to the black/white and green/red wires.

It sounds more complicated than it is. just put the resistor pack inline with the fuel pump wire you have on this car. Two wires and you're done. If you pick the wrong set, it won't work.

get the car tuned?

^ You can't always fully "tune out" a steady state increase in fuel pressure.

spend 200 and get an aftermarket fpr with -6an lines and some fittings? Or sell the pump and buy a smaller one?

I found the problem :rolleyes:

We got a new fuel pump and the same thing happened.

Hooked up a FP gauge and 170psi :(

After checking all sorts like how much fuel was comming out of the return = a dribble, and even drilling out a FPR so it was just straight through and still getting the high reading, I pulled the pulsation damper off and found the previous owner had somehow managed to get a washed jammed in there blocking it off almost completey :icon_no2:


Took it out and put it all back together and 40psi and running a WHOLE lot better. :lol:

Expect the unexpected!