A high pressure pump system (14) for use with a hydraulic engine system (10), such as a fuel injection system (10) or a compression release brake system, provides variable delivery of pressurized fluid using sleeve metering principles. The relative position of metering sleeves (56) with respect to pumping pistons (32) is controlled electro-hydraulically by a control circuit (60, 160). The control circuit (60, 160) receives pressurized fluid from the pump delivery gallery (50) or another high pressure area (50, 52) and, using a pressure reducer (64, 164), reduces the operating pressure within the control circuit (60, 160) to a substantially constant pressure lower than the pump output pressure. Lower operating pressure within the control circuit (60, 160) improves the manufacturability of the control circuit components and helps to achieve better control of the pump output.