I know what you're saying I'm saying you aren't correct. FPR is affected negligibly from back pressure from siphon jet when working properly.

The siphon jets take about 15psi to operate properly and they get the "leftovers" from the fuel pressure regulator. It's not like a+b=c math eg 65psi from the pump to the FPR then 50 to the engine and 15 back to the tank but it's something like that.

The FPR is defective if the backpressure from the jet pumps is affecting the set output pressure.

The output pressure is nearly instantly adjusted you should not see more than 1-2psi difference at the rail and almost always if you see a dip in pressure it is the fault of the pump which must supply the excess pressure to supply the set 50psi forward and 15-19 psi return to the tank to operate the jet pumps.

When the pump can't supply enough PSI to supply enough volume at 50psi going to the engine it is remotely possible the back pressure from the jets could help supply a fraction of a PSI but the difference in back pressure from full to empty is only 0.5 psi where the jet pumps operate at 15-19 so only about 2-3% difference full to empty. You won't "feel that" you will feel when the electric pump drops to say 60psi and gets only 45psi to the rail because that is a TEN PERCENT drop in fuel delivery at WOT which means 225hp is suddenly 180hp and pushing 5000# you will definitely feel that every time.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)