So if you installed a After Market FPR, and set it to 43.5PSI, would you be lean now since the MAX fuel pressure you would see is say 64.5PSI on 21 PSI of boost?


Does the stock FPR being over run at 52PSI mean that it STAYS at 52PSI UNTIL teh boost needed to make teh FPR increase the fuel pressure from 43 to 52 (9PSI) is reached? Or does it simply raise from there, meaning with a Base Fuel Pressure of NO 52PSI, with 20PSI of Boost you hit NOW a 72PSI of fuel pressure?

Help?

It shouldn't. Unless the fuel pump in the Evo is duty-cycle regulated (like a Focus) the pump just pumps and the regulator opens the return line when the pressure is higher than its set point. If there's too much of a restriction on the way back the pressure will increase until the flow out equals the flow in. If the flow in stays constant then as you squirt more fuel out the injectors some of the pressure is released and the regulator can get closer to its set point.

Dave

Say that again?


I am saying I Think the FPR is STUCK at 52PSI until it see's atleast 9 PSI of boost from the Turbo (43PSI + 9PSI of fuel over run=52PSI) and THEN it increases the Fuel pressure on a 1:1 Basis, so at 20PSI, you would see 63PSI of Fuel Pressure on a STOCK Fuel rail.


I am hoping that adding a FPR that can turn DOWN the Base Fuel Pressure to 43 PSI and STILL hit the same PSI above. The other alternative is that the Stock FPR starts at 52 and goes to 72 with 20PSI of boost But I do not think it does this.

If I were you, and if my car were dyno tuned at the present, I would not change anything until I could find my way to another tuning session, whereby I would upgrade the FPR and retune simultaneously.

Doing that THIS Saturday

In that case, get your hands on a FPR ASAP.

Comes in tomorrow, tune goes on Saturday

I don't think it's stuck, and I'm not sure I know what you mean by that! You said you're only running rich around idle, right? Your larger pump is trying to push a lot of fuel into the rail. At idle the stock FPR has opened its return valve as far as it can go. Apparently it's not enough, so the pressure builds up to 52psi. When the engine needs more fuel or the manifold pressure increases the FPR closes the return line to keep the pressure up -- it doesn't have any problem doing that! I'll bet it's doing just fine maintaining the correct pressure when the engine is under load, even without positive boost.

I think someone's already brought this up, and maybe Ted can comment, but if the ECU tries to adjust fuel trims based on idle behavior (where fuel pressure is higher than what the ECU thinks) then what happens in open loop under load when the FPR is able to bring the pressure to what the ECU thinks it should be? Seems like you might run lean.

Dave

If you can't run teh proper fuel pressure under with the stock Fuel injectors then you will run rich and your idle will suffer. My car is running rich, I think a FPR will cure this and I will tune it right after. Having a 100%Linear fuel curve is important especially for just crusing around or off boost. Is it necessary? No, especially WOT as you will have the fuel there either way, I just want it the way it was when it was designed.

It is stuck at 52PSI and can't drop belowthat, so at 10PSI of BOOST or less and into vaccum, you have 52PSI of fuel Static . It is supposed to dop on a 1:1 ratio all the way down to a proper Base Fuel Pressure of 43.5 PSI and BELOW for vaccum.


With this mod give you ANY power, nope, BUT it will ensure proper fuel control, probably aid in spoolup and do something about those Fireballs I have been shooting . It will also allow you to run close to stock until WOT then you can have all the fuel you need and the idle/Gas Milage/Save your plugs/ WAY easier to tune and so on

You are over thinking this. The regulator will still add 1psi/1psi of boost. It doesn't care that base is now 52 from 43. Your fuel curve is still linear.

I'm not sure about whether or not the pressure gets stuck at 52 psi until you build 10 psi of boost, but I'm fairly certain that stock fuel pressure will not drop below base fuel pressure due to vaccuum. The fuel pressure regulator is not allowed to see vaccuum due to the fuel pressure solenoid, so the fuel pressure does not increase until positive boost is attained.

I don't agree. FPR solenoid is there for cold/open loop conditions to bump oil pressure back up to 43.5 to richen the car.
The FPR is 1:1. Regardless of base fuel pressure it will raise it for every psi of boost up to the max pressure obtainable from the fuel pump/system.

Idle fuel pressure with hose connected is 33.
No hose is 42 to 45

I have 680s and im making good power with about 23-24 psi and an agressive tune.

Oil pressure Timmy?

It goes up and down. I don't see how it could start at 52PSI. I mean it is now STUCK at 52 right? SO it can't return ANY less fuel then that, and as the boost opens I think it may creep up a little but not fully till 10PSI or so is hit then a 1:1 ratio.