b'The InternalsTwo pistons in the high pressure pump generate the necessary pressure in the fuel system. The inletcamshaftdrivesthehighpressure pump mechanically. The maximum fuel delivery pressure is 120 bar. There is a volume control valve on the high pressure pump. If youve been servicing and repairing MINIsThevolumecontrolvalve for any length of time, the topic of high pres- adjusts the flow of fuel from the sure fuel pumps is a familiar one. The secondlowpressuresideintothehigh generation of MINIs introduced the concept inpressure side of the high pressure the S models which, along with other improve- pump. This achieves the desired rail ments,boostedhorsepower,butnotwithoutpressure. The volume control valve somebirthingpains.Highpressurepumpis forced to open hydraulically by failures and carbon buildup highlightpressure in the high pressure side the top of the list.ofthehighpressurepump.The volume control valve is a compo-The BasicsWhen most of us were introduced to gaso-line direct injection, the diesel guys had a head start on us. The concept of a high pressure fuel rail, or common rail, was limited to our experience with port fuel injection. The pressure was constant throughout the system. Ingasolinedirectfuelinjection,twopressureTobeconsis-systemsareutilized.Ahighpressurefuelcontroltentwithtorquedemandandenginespeed,high system is necessary for fuel preparation and meter- pressure fuel delivery has to be adjusted to values ing, whereby a low fuel pressure line from the fuelbetween 5 and 12 mPa. (Note:BMW denotes pres-pump module within the tank is boosted by the highsuresinmegaPascals.OnemPaisapproximately pressurefuelpumpandadjustedtoadesired145 psi. You may also find some specs specified in set-point fuel pressure.suredandcon trolledwiththehelpofthefuel bars.) Therefore the fuel pressure in the rail is mea-The high pressure fuel system consists of a commonvolume control valve.fuel rail for all high pressure injection valves, a fuel rail pressure sensor, a high pressure fuel pump withAccordingtothedesiredfuelpressureset-point a built-in fuel volume control valve, and an over- value, the pre-control calculates the driver-signal for pressure valve.the fuel volume control valve.31 34'