we have upgraded the hpfp on simos 18.1 equipped car.
the pump used is a factory pump and so the fuel mass per stroke value from the original software has been copied to the software of the car.

this seems to work ok, however the fuel mass delivered by the pump during idle is about 3* the injected quantity.
the pdf states the fuel mass should be equal to the injected fuel mass. this large variation causes the ecu to pulse the vcv on the pump. this pulsation of duty % causes a negative and positive deviation of act bar vs req bar fuel pressure.
i have logged several other cars and the fuel mass does = the injected mass and the vcv duty % along with req/act bar stays steady within about .1 bar.

i have tested both raised and lowered fuel mass per stroke value with little success. lowering the value did help to the lower the variation however it was still large enough for the ecu to pulsate the vcv and cause an oscillation in the bar pressure.

the oscillation seems to only begin after the ecu begins to adapt fuel trims (as they are about -8% at idle currently when the car is first started).

i have read the FUSL_Fuel_pressure_actuator_control: "FUSL_Fuel_PRS_actuator_CTL-AE904B01.00E-xxxxxx-SIMOS18-xx-JJMMTT" function of the pdf many times and will read many more.

i assume there is a current or PWM value i need to transfer from the original software.
was just curious if maybe someone had a bit of insight.
maybe lpfp duty can help.

the car is usa market car, we changed the entire pump.

original pump is same as mk6 tsi gen1 motor. replacement pump is mk7 gti.

that being said, i found a way to disable the oscillation. the fuel mass is still about double but no more pulsing vcv.
when i have more time i will test a new idea to lower fuel mass at idle.