WTF!!!!!! Who knows the F/P

[red92]

OK, I hear all kinds of numbers out there SO WHAT is the CORRECT F/P?
I am having alot of problems with my fuel system and can not figure it out, here is what is going on:
Installed the dual FPDM system and the plug and play harness; checked the volts when cycling the key and found both pumps are getting 11.9 volts. got 60lb inj, GT pumps with upgraded fuel line to the hat, -6's to a Y-block, -8 up to a mallory big fuel filter, and a -8 to the fuel rail no leaks any where. I tried to tune it and it was lean and found that when cycling the key once I had 3psi then cycle it again and get 7psi that was as high as it got and it bled off to 0 but when starting the car it would run at 30psi and stay there. I put a whipple on too and have not been able to get on it yet so if anybody could help that would be great.
thanks

:beer:

 

[04CobraMatt]

39

 

[red92]

Thanks, but when it goes under boost what happens to the F/P?

 

[04CobraMatt]

Thanks, but when it goes under boost what happens to the F/P?

39 ;-)

 

[11ride4life]

39 ;-)

Are you sure?

I thought that FP had to go up one pound per pound of boost to overcome manifold pressure:idea:

 

[04CobraMatt]

As i understand it, the FRPS uses vacuum/boost as a reference to calculate pressure in the line, the Actual fuel pressure is always being corrected to 39, boost or not.

 

[red92]

So the needle on my fuel pressure gauge should not move at all from the point that I turn on the car and idling all the way up to WOT?

 

[04CobraMatt]

So the needle on my fuel pressure gauge should not move at all from the point that I turn on the car and idling all the way up to WOT?

It will cycle between 36-42 and sometimes spike at 60 when you get off the throttle from a WOT, but roughly yes.

 

[red92]

so it's not good if it were to go to 30psi as the RPM's are going up?

Man I hate looking for a ghost!

 

[Posi]

On a WOT pull on the dyno mine was at 38.66 I think.

 

[Nutty 5.0]

It just holds the injector open longer = pulse width I believe. Someone can confirm I hope. The pressure it seems stays constant on these cars for the most part.

 

[04CobraMatt]

It just holds the injector open longer = pulse width I believe. Someone can confirm I hope. The pressure it seems stays constant on these cars for the most part.

Thats right.

 

[RealBadDude]

i have had a fuel pressure gauge installed since the car was new. i have no pully or fuel mods.

my stock fuel pressure is around 30 at idle and goes up to just over 40 at WOT.

as said that is stock fuel system and boost levels.

also according to AllData (the cracked 9.30 version i have w/ no hardware key)

says fuel pressure should be:

engine running: 27-37 psi
key on engine off: 30-50 psi

hope that helps.

 

[RealBadDude]

Are you sure?

I thought that FP had to go up one pound per pound of boost to overcome manifold pressure:idea:

correct.

 

[04CobraMatt]

So the needle on my fuel pressure gauge should not move at all from the point that I turn on the car and idling all the way up to WOT?

I was not understanding the difference between Actual Fuel-pressure and Pressure Drop accross the Injectors.

This put things in perspective for me.

Vac is normal at 20inhg. You lose 1psi of fuel pressure for every 2inhg.
Ford has a base fuel pressure or what they call pressure drop of 39. So if you lose 10psi at idle you should be around 29. At wot, fuel pressure increases the same.
For every psi of boost you will get an increase in fp to about 55 give or take.
If a mechanic is watching this on a datalogger they will see 38-39 at all times as they are watching the pressure drop accross injectors and not fuel pressure.

 

[fjules]

You might want to read this:

http://www.modularfords.com/forums/f17/understanding-our-fuel-system-91066.html

 

[ShelbyGuy]

39 delta P
cant really add anything that fjules didnt post over on that place where the fords are modular