Fuel Pressure for MFI?

[422flat6]

Is 10 psi adequate, measured at the rear most connection to the fuel console (i.e. the return hose from the MFI pump)? I have cleaned the strainer, replaced all fuel hoses, replaced fuel filter and replaced the overflow check valve. Replacing old kinked hoses increased pressure from 2.5 psi to 9.0 psi. Replacing overflow valve increased pressure to 10.0 psi.

I know the spec is 11.8 +/- 3.0 psi. I was really hoping that replacing the overflow valve would get me to at least 11.8 psi. Want to make sure that I have adequate fuel pressure before adjusting mixture at the MFI pump. I don't know what else I could do to raise pressure. I have tried measuring pressure with the gas cap off to make sure it's not a tank venting issue. I have tested the electric fuel pump and it is capable of over 30 psi.

[gled49]

It doesn't matter that much. My MFI race car has a fuel pressure gauge mounted in the fuel filter console at the cold start selinoid fitting, as I don't need cold start. Fuel pressure in the AM can run as high as 13-14 psi, in the afternoon in hot weather the pressures drop as low as 8 psi. It always run perfect. I never would of guessed there was that much fluctuation in fuel pressure based on temp and atmospheric conditions.gordon

[422flat6]

Thanks for the sanity check. I'll try to get some data points at different temperatures just for my own curiosity.

[gled49]

BTW my gauge is in the the cockpit so pressures are real time driving conditions. G

[Richardnew]

My 911 runs about 4 psi. The pump was designed for an MFI system.

You might want to talk to the folks at Fuel Injection Corp. Give them the numbers from your pump and they can tell you exactly what you have. My "original" pump turned out to be a pump for an MFI system. It was actually built in 1984.



It's always interesting to find out how non-original your original car might be.

Richard Newton
Fuel Filters