Abstract: An oil pump for use in a vehicle engine includes a rotary pump for pressurizing oil to be pumped, and a movable piston cooperating with the rotary pump to facilitate metering of oil to and from the pump. The oil metering device is incorporated directly into the pump by means of a cam-actuated piston or a spring-loaded piston which cooperates with a displacement chamber for metering oil. Alternatively, a solenoid-actuated piston may be provided for selectively blocking pressurized fluid from entering a spring-loaded diaphragm chamber. The diaphragm is stroked alternatively by a spring and by oil pressure for metering of fluid therethrough in desired increments.