Cascade Crew

fiveoformula · Posted: Sat Apr 30, 2011 7:24 pm Post subject: fuel PSI

whats the rule of thumb on deadhead fuel pressure?
Im working on a '93 Ford Aerostar van, runs very rough at idle, throws a lean code and o2 voltage sits at .10- .17 all the time. fuel pressure is in spec at an idle (37psi) but I could not find a dead-head spec, and it made 70psi key-on.

blue89 · Posted: Sat Apr 30, 2011 10:11 pm Post subject:

I think I hit 80-90 psi on mine. Make sure the pressure doesn't bleed off after it pump UPS.

fiveoformula · Posted: Sun May 01, 2011 1:32 pm Post subject:

Actually it does, goes from 70 down to 55, and also when its running at 35psi, it drops 5 or 6psi if you tap the throttle, but not if you snap it all the way.

blue89 · Posted: Sun May 01, 2011 3:44 pm Post subject:

After a few hours of not running, key on so the pump primes. The fuel pressure should fall too much. Not more than 10psi in 20 seconds?

fiveoformula · Posted: Sun May 01, 2011 6:13 pm Post subject:

Yeah it did it in less than 20 seconds, it went down just after the pump stopped priming.

Twilightoptics · Posted: Sun May 01, 2011 10:10 pm Post subject:

Clamp off the return line. If the pressure bleeds down still, it's injector or fuel pump not holding the pressure. If it doesn't bleed down, the regulator is bad.

fiveoformula · Posted: Sun May 01, 2011 11:04 pm Post subject:

This happened when I dead-headed the pump, I took the fuel filter out and put the gauge on the line straight from the tank, so really the only thing it could be is the pump not holding pressure, if im understanding it right... I did it that way because I couldn't find any rubber line to pinch.

Twilightoptics · Posted: Sun May 01, 2011 11:08 pm Post subject:

So it's 70psi key on dead head.

Holds? 55psi dead head after the pump cycles off?

The deadhead pressure is not a valid tool. You're only testing the max pressure it puts out. And you will get two different readings one with the pump on, and one when it stops.

Dropping 5psi when you rev is not good. The pressure should increase when throttle is applied as vacuum decreases.

Check it under a heavy load. If it drops steadily then you have a delivery issue.

If it moves like a vacuum gauge it's okay and the regulator is vacuum controlled like a TPI car.

If it stays the same the whole time, it's probably fine and is not a variable regulator that runs on vacuum.