Abstract: A cartridge vane pump for a motor vehicle power steering system exhibits improved cold start performance. The pump includes a plurality of radially disposed vanes which are received within a rotor which is rotatably supported within a cylindrical cam ring defining two diametrically opposed pumping lobes. An inlet (upper) section and an outlet (lower) section engage the ends of the cam ring and define suitable passageways which provide fluid into and out of the pumping lobes. Under vane porting in the inlet section provides high pressure fluid to the inner edges of the vanes received within the rotor as they traverse the intake portions of the pumping lobes urging the vanes into contact with the cam ring surface.