SilvioRX7

The car started to stumble as soon as it would come into boost like 1 -2 psi. I checked the voltage at the pump, when the engine was reved it would only go from 7v at idle to 9v WOT. So...I wired the pump to 12v and went for a ride. When I hit WOT it was fine up until the boost hit 12 psi, the fuel pressure went from 60lbs down to 40lbs. I took apart the regulator and it seemed fine, there were no pits in the ball or on the seat. I'm going to check the fuel filter tomorrow.

Any help would be greatly appreciated.

Thanks,
Silvio

maxcooper

Start with an understanding of what the fuel pressure should be:

Base pressure is set with the manifold reference hose disconnected from the FPR. It is usually in the 35-50 psi range. Let's choose 40 psi base pressure for this example. The difference in pressure between the manifold and your fuel rail should always be equal to this base pressure. Maintaining this constant difference in pressure is precisely what the FPR is supposed to do.

At idle, you will have some manifold vacuum, so the fuel pressure indicated on a fuel pressure gauge will drop below the base pressure. For out 40 psi base pressure example, 32 psi might be typical, though it really depends on how much vacuum your engine is pulling. The exact number doesn't matter all the much -- just don't be surprised that it drops below the base pressure.

Under boost, the fuel rail pressure should be equal to your base pressure plus the boost pressure. For our example with 40 psi base pressure and running, say, 12 psi of boost, the fuel pressure gauge should read 52 psi.

Potential problems:

- If your fuel pump is failing, inadequate, or you have a leak or a pinched hose before the FPR, the pressure can be lower than expected. This is especially likely under full boost at your power peak (~7000RPM), since this is the time that the engine needs the highest flow at the highest pressure. However, if you have a known problem, I don't recommend boosting!

- If the pressure is too high, you might have a pinched return line. This is most likely to happen at idle.

-Max

SPOautos

No one will be able to give you any good specific advice on your particular problem unlesss they know your setup.

Sounds like the vac line going to the fpr blew off when under boost

pistonsuk

[QUOTE=I'm going to check the fuel filter tomorrow.[/QUOTE]

good idea.

after installing a wb255 my pressure would intermitantly drop. i could "reset" this situation by turning the car off and back on. apparently this would allow the chunk of whatever to drop back out of the way in the fuel filter.

considering the filter was only 9mo old, i only found this problem after: rewiring directly to 12V, exchanging the pump, disassembing the regulator and scratching my head alot...

good luck,
justin

SilvioRX7

I replaced the fuel filter and the regulator and went for a ride, the problem seemed fixed. Then I went out Friday night and it did it again. I took out the pump and checked the filter on the pump, the filter was clean. I went for another ride...the car pulled great through all the gears??? I don't know if the pump is going bad or what? (now I'm scratching my head alot)

ghostrx7

silvio your car has west palm beach rx7 syndrome.

jasrx

in my case my fuel pressure at idle was 80 psi
it turned out to be the factory reg was buggerd , i put a malpassi reg on and its been fine ever since