Druken

Just a quick question, I was wondering how much pressure is required from the FPR for the fuel to flow properly because I was going to buy an adjustable one off of ebay. The FPR is required no matter what correct? Even if I have a surge tank?
Thanks

Turblown

iTrader: (12)

Most common base fp is 40psi. Yes you need one even if you have a surge tank.

V8slayer

+1 40 psi is the most common

NZConvertible

Stock static fuel pressure is 37psi. Unless you have a fuel controller or programmable ECU, that's where you should set it. If you can alter fuelling to suit a higher pressure, you can pretty much set it where you want as long as your pump can maintain that pressure (plus boost pressure for turbos) right through the rev/load range. 40-45psi is normal.

scathcart

To add to this:
You COULD set it to whatever you wish, but you wouldn't want to. Atomization suffers with both higher and lower rail pressures. Set it lower, and the fuel spray pattern is not as finely "misted", set it higher and the fuel tends to spray more on the the opposing runner walls, especially on the primaries where the intercept angle is close to 90 degrees. The only reason to increase the fuel pressure is when high volume injectors are installed, where the spray pattern is already quite poor and atomization suffers, or when the intercept angle is more optimized on an aftermarket manifold.

hhn2002

what if my static was 43psi and all fuel pressure is lost in literally 10seconds once key is removed. note: this is all without the engine running.

FPR? or leaky injectors?

will the secondary fuel rail from an s4 fit an s5?
will i need to use the s4 injectors if it isnt plug and play?

Spectator

iTrader: (1)

fire hazard.

The Wankler

iTrader: (14)

S5 will fit the S4. No need for different clips. S4 is a better fuel rail anyhow in regards to modifying it. Notice the Pulsation dampener is welded on the S5 rail. It is screwed into the S4.

hhn2002

it cant be a fire hazard when it cant stay running. haha

hhn2002

well im just replacing the secondary fuel rail(the one with the FPR welded on; not the primary) so if s5 secondary rail will fit s4 then the opposite is also true?

HAILERS

There's a checkvalve built in the pump that keeps the pressure from decaying. If it isn't working, then the pressure will drop like a rock.

I guess it could also be the FPR. Just put the pressure gauge at the fuel filter outlet (deadhead it) and turn the pump on, then off. The pressure should go to what??? no manual here, 80psi approx? So if it decays right away like you stated in your thread, then it would be a pump checkvalve problem. If it does not decay right off, then it's the FPR or bad *** leaking injectors. But if it was leaking injectors you wouldn't be able to start the engine because it's flooded. That'd be a lot of fuel leaking in 10 seconds.

The Wankler

iTrader: (14)

Ya know, I was going to write FPR, but got *** backwards on it.

Druken

So the FPR should stay at 40psi no matter what? I adjusted mine to approx. 40psi, since it seems anything around 40 would be okay, when the car was at idle then it goes back down to 0psi after maybe 2-5 seconds when the car is off. That's normal right?

As for the high volume injectors, I don't think I do have them, but I have a s5 n/a with 460(?)cc primaries and 550cc secondaries. Since I didn't upgrade the injectors drastically, 40psi should still be good right? Can't hurt to ask. Heh

hhn2002

ok cool thanks hailers ohh and for future reference in the fsm it says the maximum pressure for fuel pump should be about 71.1 to 92.4 psi

hhn2002

no it should hold pressure more or less even after the engine is shut off. the fsm specifies that it should not lose more than 2.8 psi 15mins after the engine is shut off.

Druken

... Crap?

Could it be that there is a vacuum leak or something?

hhn2002

s4 secondary fuel rails do not fit s5 secondary fuel rails nor vice versa. found out the hard way .ohh well 10 bucks at junkyard didnt hurt the finances too much.

hhn2002

three possibilities exist
fuel pump
leaky injectors
fpr


well i've just found out that for me it might just be very leaky primaries as when i keep the engine revs above 4k the rpms stable out below that its completely chaos. so ill get them cleaned and report back.

Druken

I don't think I have leaky injectors, because like how HAILER stated the engine would have been flooded. And if it was flooded, then it would take a lot to start up the car... but she starts up right away now...