[D's Bimmer]

Is there a way to test the effectiveness of the HPFP and the LPFP? I am trying to determine if some shadow codes are indicators of a failing pump.

Thanks,

[orteeze]

If you have a JB4, you can review your logs; in specific the FP L and FP H.

FP L: Fuel pressure, low system. Pressure is read on the left hand scale X 10. Otherwise known as the in tank low pressure fuel pump. This value typically ranges from 55-70psi. If dropping below 50psi it indicates a problem with your low fuel pressure pump. Most often that problem is it needs to be augmented with an inline pump to keep up with the higher fuel demands required by ethanol usage.
　
FP H: Fuel pressure, high system. Otherwise known as the high pressure pump. Note all N54 include this and other platforms can only log this if also equipped with the flex fuel connector. This value represents the voltage of the high pressure 0-5V sensor, where a value of 20 is 5v. Each unit of measure is roughly equal to 150psi. Typical values at full throttle are 10-14, or 1500 to 2100psi. Values of less than 900psi as full throttle indicate a fuel delivery problem and the JB4 will failsafe at 700psi at full throttle. Note when not at full throttle a typical value is 5 or 750psi

[weehe126]

There is no lpfp sensor on N55, I swear that needs to be put in a sticky. As for testing the hpfp, you can with either rheingold or INPA I believe. I had a buddy check mine when I thought my pump was bad. Said everything was good even though I was getting long cranks. Never had a proble in my logs either and I was running E50 the whole time. For over a year I ran with long cranks then got a hpfp code. Got a new hpfp and now have normal cranks and no codes.

My point is, it is very difficult to diagnose a bad hpfp outside of replacing it to see if it fixes the problem.

[Kevin39]

I was under the impression that the N55 cars don't have a low pressure pump sensor.

Edit: Weehe beat me to it.

[orteeze]

Learned something new today.