2007 r56 n12. have an issue with no pressure at 1st start of the day, and rough idle, like a chugging sound when trying to move forward or reverse. i have to usually leave it on the ON position to prime, and wait for the rpms to settle down a bit before moving.
using a pressure gauge w/car running, pressure would be at 54psi, but when off it would drop quickly past 45psi. i replaced the fuel pump and filter. tested the pressure, this time it stayed around 48psi after 20 minutes w/car being off. from the manual and your article, it shouldn't go past .5 bars.
but i still get the rough idle. i couldnt find any apparent leaks around the fuel rail/line or under the car. does the fuel rail have a check valve or is it only the pump? could it be the fuel pressure regulator on the filter unit?
also need to mention that i replaced the fuel injectors a couple months ago but can't recall if i had the rough idle before that. i bought the car a month before i replaced the injectors.
thanks in advance
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MINI Cooper R56 Fuel Pump Testing (2007-2011) | Pelican Parts DIY Maintenance Article