BMW E39 long cranks and rough on take off

[TheRB]

hello all this is my first post and im really stumped with this issue i have been working on BMWs since i was 17 using a lot of the knowledge I've learned from everybody on this form i have a 1998 BMW E39 528i touring it has about 330,000kms on it I've owned it for nearly four years so far i have replaced the fuel pump, PCV and all hoses, done both oil filter housing and rocker cover gaskets, and some other stuff i cant fully remember but i have also replaced the crank sensor twice as it failed twice and the car wouldn't start the last one was about 4 months ago and all was going well until its started long cranking times and rough on take off only when just touching the pedal then would immediately go smooth again it stalled once but like turning the key to shut the engine off no chugging i was looking around the engine bay and noticed that i had not put a hose back onto the evap purge valve and i thought well there's the problem reconnected it took it for a drive and seemed fine but then it started playing up again i don't unfortunately have a way to scan it yet do you guys have any idea what could be wrong i feel like its the crank sensor again witch was replaced by the dealership and the car is going back there Monday if i cant fix it and help would be great

[TheRB]

right arfter posting this i checked the fuel pressure at the rail and nothing primed it with the ignition and pressure came back so its seems to be losing pressure when the engine is turned off but what could be causing that i already replaced the pump about 3 years ago

[coolpersob]

Considered doing the Fuel Pressure Regulator? Or check the screen on the fuel pump to make sure nothing is clogging it up.

[jclausen]

When the engine is shut off it should hold fuel pressure with a slight drop in psi the pump has a check valve that holds line pressure part of the pump

[JimLev]

The spec is a 7 PSI drop after 20 min.
Over night is will eventually drop to 0, which is OK.