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Old 05-02-2022, 09:42 AM
andrewwynn's Avatar
andrewwynn andrewwynn is offline
Join Date: Jun 2015
Location: Racine, WI
Posts: 9,784
andrewwynn will become famous soon enough
Three e53 brain has no way to know what is the fuel pressure so no way to report an error based on it. You will get random errors that hint at a possibility of a fuel pressure problem.

The fuel delivery is calculated based on assumption that fuel pressure is 50.00 psi. If it's anything else even briefly, the wrong amount of fuel is delivered.

When wife's FPR was defective she would have random difficult starts but other than than rarely ever any problem.

When I finally got the pressure gauge, what I discovered was the pressure at idle would vary with every pulse of injectors (think: water hammer). It only changed about 1/2 psi but so fast it basically made the needle transparent.

The defect was determined to be a 50 o-ring (4 in quantity). I replaced the whole FPR+fuel filter since they were about 20 years old and 170,000 miles and it would have taken days to source the exact o-ring.

Take a slow motion video of the pressure at idle to see if the needle is dead solid or wiggles. Then the acid test of FPR is to leave the gauge on overnight and determine if it holds pressure.

The other main test is for the pump itself: does the pressure stay constant at WOT. At end of life, the pump won't be able to produce the excess pressure needed to input into the FPR and you'll get a pressure drop at WOT but it holds fine at lower demand.
2011 E70 N55 (me)
2012 E70 N63 (wife)
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