Rail pressure is much higher than just before FPR pressure?

[turbogrill]

Hi,

 

I have just redone my fuel system ($$$): Hydramat, stainbraided lines, AN fittings, Automotive FPR, nice fuel rail, new pump, new injectors, yada yada.

I have one pressure gauge in the rail and one in the FPR (dedicated port). The FPR gauge before the regulation but not inline with the feed, it's a port on the FPR itself. So it's intended to measure pressure before regulation.

 

It's EFI, 1 rail, return system.

 

The thing is that they read very differently:

Pump on, engine off:   Rail: 40 psi,  just before FPR: 20psi

Pump on, engine on:    Rail 40 psi,  just before FPR: 0psi

 

I would think that there are no or just a slight pressure drop between the rail and just before the FPR.

 

Any ideas?

 

 

Edited September 22, 2017 by turbogrill

[Team Infiniti]

The FPR controls pressure by releasing anything over it's setting, pressure will be the same from fuel pump outlet to the regulator then virtually 0 after, at that point it is return fuel.

[Ogren-Engineering]

Pics and direction would help. As long as you have the 40 , you should run fine.

    The rail  is fed before the FPR returns the fuel to the tank.    My guess is that you have a gauge in the wrong place.  No reason for a gauge  at the FPR return line. It should be zero to 4 # as it returns. Maybe the FPR has a vacuum port for corection? 

  ED,  Mediocre minds think similar.  

Edited September 22, 2017 by flyinglizard

[turbogrill]

1 hour ago, flyinglizard said:

Pics and direction would help. As long as you have the 40 , you should run fine.

    The rail  is fed before the FPR returns the fuel to the tank.    My guess is that you have a gauge in the wrong place.  No reason for a gauge  at the FPR return line. It should be zero to 4 # as it returns. Maybe the FPR has a vacuum port for corection? 

  ED,  Mediocre minds think similar.  

 

This is a gauge port on the FPR, it's after the rail but before the actual regulation. So it's not measuring the return line. Vacuum is connected properly.

 

Pressure should be almost the same all the way up until the actual valve in the FPR right?

 

Maybe the sensor just broke  I don't think it's a bad ground because that would should high PSI and not low.

 

 

[Ogren-Engineering]

Swap the gauges.

[ABR-Glen]

The regulator is like a pressure relief valve, it goes on the *outlet* end of the fuel rail. The injectors should be between the pump and the regulator (because that is the part of the system you are regulating the pressure in). i.e. the regulator controls the pressure before it, not after it. 

[LAMR2]

Why two gauges? If you have the correct pressure in the rail, who cares what it is at some point internally in the regulator.