HIRISK

Hi Guys,

I was just wondering if someone can help me with a question on fuel pressure.

I currently have a fuel pressure gauge tapped into the fuel line BEFORE it enters the FPR. I have done this as I wanted to test the pressure that the pump was generating.

Now, I understand that if you test the fuel pressure at the regulator it should be 38psi (+/- 1psi) at idle and 43psi (+/- 1psi) at idle with vacum line removed (i think that is right??).

But, what should the pressure be at the point I have tapped in my fuel pressure gauge??

From memory, EFI pumps make about 60 to 70psi??

Thanks in advance.

ws6transam

Your fuel pressure, before the regulator, should be 35 to 43 PSI. The regulator regulates fuel pressure in the rail, and the pressure in the rail is supposed to be the same as the pressure in the line, all the way back to the pump. The pressure AFTER the regulator should be near zero, as there should be no further restrictions to the fuel that gets returned to the tank.

Your EFI pump pressure of 60 - 70 PSI represents the DEAD-HEAD pressure of the fuel pump. i.e. the highest potential pressure that it can produce when pumping into a dead line. As the pump pressure increases, it's fuel flow rating decreases, and 60 - 70 PSI is the point where the pressure rises until flow drops to zero. In reality, you do not run the pump at this pressure. You run it at whatever the regulator is set at.

HIRISK

Thanks for the reply - much appreciated.

I am basically trying to pin point an intermittent problem.

The car is all good, then for no reason starts to splutter and almost dies all together. It then does not really want to accelerate and splutters. If I then pull over and shut it dpwn then a minute or two later restart it - all good?

I am just trying to figure out if the pump OR the regulator are stuffed.

The only thing that concerns me with the pump is that I tapped a gauge in BEFORE the regulator and only get about 35psi. I thought it would need to be 43-4psi?

ws6transam

You know, the fuel pressure on my TPIS miniram is usually around 37-38 PSI. So I think 2PSI difference won't explain it. Can you watch the pressure when the malfunction occurs? If its not dropping much, then it's probably not the fuel delivery.

87tpita

Check the iac, reset it according to the steps on thirdgen.org. Also check the tps to ensure its working properly.