A HEUI system uses a fixed displacement, axial displacement pump to provide a generally constant pump flow of high pressure hydraulic fluid over the operating speed range of the pump to minimize parasitic power drains on the engine. The axial piston pump includes a orificing suction slot to vary the pump displacement over the operating speed of the pump. A throttling valve at the pump inlet may be provided to starve inlet fluid feed if reduced flow to the injectors is additionally required.