ENGINE COMPONENT AND LOCATION 99 There are four phases to the injector cycle of operation. These include: Fill phase Spill phase Injection phase Pressure drop phase Fill phase (A) : During the filling phase, the pump plunger is on its way up, the camshaft lobe is passing its highest point and the rocker arm is on its way toward the camshaft base circle. The fuel valve is open, allowing fuel to flow into the unit injector from the lower fuel gallery. Fuel flows into the cylinder head and the unit injector pump cylinder. Filling continues until the pump plunger reaches its upper position. Spill phase (B) :
The spill phase begins when the camshaft lobe forces the rocker arm to push the pump plunger down. The fuel can now flow through the fuel valve, through the holes in the unit injector and out through the fuel gallery. The spill phase continues as long as the fuel valve is open. W2033330 1.Pump Plunger 2. Fuel Gallery 3. Injector Nozzle