GASOLINE DIRECT INJECTION FUEL PUMP WITH ISOLATED PLUNGER SLEEVE

An improved high-pressure fuel pump for a gasoline direct injection system is provided. The fuel pump includes a pump body defining a low-pressure side, a high-pressure side, and a pumping chamber therebetween. The pump body also defines a central bore and a drain port extending from the central bore to the low-pressure side. A slip-fit sleeve is clamped within the central bore, the slip-fit sleeve including upper and lower guide ribs. A plunger is moveable within the sleeve for compressing fuel within the pumping chamber. The plunger and the sleeve define a first diametral clearance, and the guide ribs and the central bore define a second diametral clearance. Fuel diverting around the upper guide rib during pumping operations can recirculate through the drain port to the low-pressure side. To accommodate thermal expansion of the sleeve, the second diametral clearance is at least 75% of the first diametral clearance.