PhoKing714

iTrader: (21)

I have 850/1600 w kg rails, ss lines, fpr. At idle, fuel pressure is at 33. With my single turbo setup, I'm only boosting 12-13 lbs., as pressure starts to drop anywhere above that boost amount. My shop told me that idle pressure doesn't matter, that I need better fuel pump. I current have walbro 255. Should I bump my idle fuel pressure up? What should it be at? Is my shop/tuner wrong?

limepro

iTrader: (2)

first thing to do is find a rotary shop, don't let just anyone touch your cars as they have less give and a rotary specialist will know what to do.

PhoKing714

iTrader: (21)

This is from a well known shop rotary specialist in Southern California.

limepro

iTrader: (2)

Then no reason to second guess them, although there is nothing wrong at all with getting more info, if they are reputable they most likely know what they are talking about.

C. Ludwig

iTrader: (27)

They're corect. If the fuel pressure is dropping under high load, then the fuel pump isn't moving enough volume. Raising the base pressure will likely make the situation worse. Pump volume will drop as the pressure rises, so asking it make more pressure at a volume it already can't produce is not the solution.

Having said all that, a Walbro 255 in good shape should flow plenty of fuel for any stock or street port engine at that boost level. Veryify the pump is getting good voltage and the wiring is heavy enough to supply the necessary amperage.

Also, verify the fuel filter is not clogged or you have some other form of restriction like the fuel sock on the pump being clogged or a damged line.

wstrohm

On page F-60 (and also F-108) of the 1994 workshop manual, operation of the "fuel pump relay (speed)" is illustrated. PCME terminal 1K controls the relay. Terminal 1K is the signal return for the speed relay coil. (See also page Z-28 of the manual.)

Terminal 1K voltage "high" = "speed" relay contacts open, i.e. pump resistor in circuit; 1K voltage "low" = contacts closed, i.e. fuel pump resistor jumpered.

The manual states on page F-108 that "high speed and heavy load" should cause terminal 1K to go low, and also activation of the PRC solenoid valve should cause terminal 1K of the PCME to go low. (Also see page F-154.)

So on a stock FD fuel system, there should be a jump in voltage at the fuel pump (also at the white/red wire at the speed relay) when terminal 1K of the PCME (blue wire with white stripe at the speed relay) goes low. If that is not seen, there is a problem with the relay itself (open coil or oxidized contacts).

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Page F-111 shows that a "high" voltage output from PCME terminal 4M activates the PRC solenoid valve, so a "high" voltage on 4M also causes a "low" voltage at terminal 1K. So under hot start conditions, fuel pressure should rise from the combination of opening the PRC solenoid vacuum hose connection to the fuel pressure regulator and the jumpering of the pump resistor by closing the "speed" relay.
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Maybe this info will be helpful if troubleshooting the fuel pump "speed" relay.

Gorilla RE

iTrader: (1)

simple bolt-on street setup, run 42-45psi (set with no vac). For your issue, check your filter, electrical signal and ground to the pump, make sure that the high speed relay is being engaged under load and don't rule out the fuel pressure reg.

-J

scotty305

iTrader: (2)

It's not a bad idea to double-check the fuel lines inside the fuel tank. A loose connection or torn line inside the tank would cause a drop in fuel pressure.


Another option could be to use a multimeter and measure the voltage between the fuel pump power and ground wires. This could help track down a problem in the power supply (for instance, if the fuel pump speed relay isn't operating properly), or a problem in the ground wiring.

Gorilla RE

iTrader: (1)

VERY true

-J

JonnyQuestions

iTrader: (8)

turn key to on position and under the hood in the diagnostics box jump GND and F/P together and see what your base fuel pressure is. Now you can check for fuel leaks by cranking up the pressure with the regulator +15psi or whatever you plan on boosting and check around for any fuel leaks. Also have you rewired your fuel pump? Stock wiring has been proven in most cases to handicap the fuel pump

JonnyQuestions

iTrader: (8)

Good idea to check that little rubber hose from walbro to hardline. If you didnt use a submersible fuel hose i bet that that rubber line will be all swollen