HIGH PRESSURE FUEL PUMP

The invention comprises a high pressure diesel fuel pump (20) comprising a pumping assembly (30) and a drivetrain assembly (40). The pumping assembly (30) comprises a plunger (32) extending from a pump head (34) along a pumping axis (A-A'). The drivetrain assembly (40) comprises a drive shaft (42) and a cam (44) mounted thereon within a cambox (46) of a housing (48), a plunger-driving assembly (50) for contact with a lower end (32a) of the plunger (32) and mounted substantially between said plunger (32) and the cam (44). The plunger (32) is arranged for reciprocating linear movement along the pumping axis (A-A') within a pumping chamber (36) of the housing (48) upon rotation of the cam (44). The pumping chamber (36) comprises a pressure regulating member (60, 80) adapted to adjust its volume in response to changes in pressure in the cambox (46).