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A fuel injector pump in a direct-injection fuel delivery system for an internal combustion engine including a solenoid valve for controlling transfer of fluid from a high pressure chamber to a fuel injector nozzle. A supply passage and a return passage provide a fuel flow circuit for the fuel delive

A fuel injector pump in a direct-injection fuel delivery system for an internal combustion engine including a solenoid valve for controlling transfer of fluid from a high pressure chamber to a fuel injector nozzle. A supply passage and a return passage provide a fuel flow circuit for the fuel delivery system, the high pressure chamber being defined in part by a camshaft-driven plunger. An independent fuel leak flow path is provided to accommodate fuel leakage past a plunger of the pump, the fuel leak flow path extending to a zero pressure fuel tank.

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1. A fuel injection pump assembly for an internal combustion engine comprising an injector body defining a cylindrical fuel pumping chamber, a plunger mounted for reciprocation in the pumping chamber, a high pressure fuel delivery passage extending from the pumping chamber to an injector nozzle;a co

1. A fuel injection pump assembly for an internal combustion engine comprising an injector body defining a cylindrical fuel pumping chamber, a plunger mounted for reciprocation in the pumping chamber, a high pressure fuel delivery passage extending from the pumping chamber to an injector nozzle;a control valve in the fuel delivery passage, an actuator for the control valve for establishing and interrupting delivery of fuel from the pumping chamber to the injector nozzle;a cam mechanism driven by the engine including a cam drivably engageable with the plunger whereby the cam mechanism strokes the plunger in a stroking direction to effect high pressure fuel delivery to the injector nozzle, the cam mechanism being in communication with lubrication oil in the engine;a fuel supply passage in the injector body communicating with the control valve;a flow return passage in the injector body communicating with the control valve;a zero pressure leak flow passage in the injector body;the zero pressure leak flow passage being independent and separate from the fuel supply passage and the fuel return passage;at least one fuel leak flow port in the pump body communicating with the pumping chamber and located relative to the plunger whereby it is covered by the plunger as the plunger is stroked, the leak flow port extending to the zero pressure leak flow passage;the plunger displacing fuel in the pumping chamber as fuel is delivered by the high pressure fuel delivery passage to the injector nozzle; anda predetermined dimensional clearance between the plunger and the pumping chamber defining a leak flow path leading to the leak flow port from the pumping chamber as the plunger is advanced in a pumping stroke by the cam mechanism, thereby avoiding mixing of fuel with engine lubrication oil. 2. The fuel injection pump assembly set forth in claim 1 wherein the actuator for the control valve comprises a solenoid forming a part of an electronic controller responsive to engine operating variables for establishing fuel flow from the pumping chamber through the control valve to the high pressure fuel delivery passage when the control valve is moved by the actuator to a closed position and establishing fuel flow from the fuel supply passage through the control valve to the pumping chamber when the valve is moved to an open position. 3. The fuel injection pump assembly set forth in claim 1 wherein the leak flow path is defined in part by a flow path created by the predetermined dimensional clearance, the zero pressure leak flow passage extending to a fuel supply tank. 4. The fuel injection pump assembly set forth in claim 1 wherein the leak flow path is defined in part by an annulus formed in the plunger, the annulus communicating with the leak flow port as the pump plunger is stroked by the cam mechanism whereby fuel leakage around the pump plunger escapes through the leak flow port. 5. The fuel injection pump assembly set forth in claim 2 wherein the leak flow path is defined in part by an annulus formed in the pump plunger, the annulus communicating with the leak flow port as the pump plunger is stroked by the cam mechanism whereby fuel leakage around the pump plunger escapes through the leak flow port. 6. The fuel injection pump assembly set forth in claim 3 wherein the leak flow passage is defined in part by an annulus formed in the pump plunger, the annulus communicating with the leak flow port as the pump plunger is stroked by the cam mechanism whereby fuel leakage around the pump plunger escapes through the leak flow port. 7. The fuel injection pump assembly set forth in claim 1 wherein the engine comprises an engine housing configured to support the injector body, the zero pressure leak flow passage extending from the leak flow port through the injector body to a leak flow outlet location on the injector body that is external of the engine housing. 8. The fuel injection pump assembly set forth in claim 7 wherein the zero pressure leak flow pas sage extends from the leak flow port through the injector body in a direction that is generally parallel to the stroking direction of the plunger. 9. The fuel injection pump assembly set forth in claim 8 including a zero pressure leak flow passage connector at the leak flow outlet location whereby leak flow is returned through a conduit to a zero pressure tank.