The factory manual states that there should be a residual pressure of at least 36psi (2.5bar) in the fuel rail after the engine is turned off. This is precisely the case when I use a stock fuel pressure regulator.

I recently purchased a stock-fitting adjustable fuel pressure regulator from 034 Motorsport. When I turn the engine off with that AFPR installed, pressure in the line immediately drops to 0. There's no residual pressure whatsoever.

So my question is: why does the manual state there should be a residual pressure? Is it actually needed for some reason?

I did notice that the engine needs to crank a bit longer before it catches when I use the AFPR vs the OEM FPR. I do let the fuel pump pressurize the system first (my other vehicle is an old diesel pickup, I'm trained to wait for glow plugs, even when there are none), but it still takes sometimes twice as much cranking before the engine catches. Seems odd to me, but 034 Motorsport claims this is normal behavior.

 

The only reason for residual fuel pressure is so that the car starts more easily. Having to crank for longer is pretty normal with many after market FPR's. I have the same problem but on a different car. It might be worth asking 034 if this is normal for their item or whether its just a poor seal on the check valve mating face.

 

Thanks! That confirms what 034 Motorsport said, so I'm satisfied.

 

my pressure drops to 0 after a couple hours and i have no issues starting it up. im running a ecs tuning afpr. its weird that it drops off immediately but not weird that it drops off to zero. as long as it starts and maintains fuel pressure after started there shouldnt be any problem

 

yeah, pressure is maintained just fine. Although the gauge needle is a bit more jittery with the AFPR than with the OEM FPR. But the difference is minimal.