Question 45 UFIV01 - Chief Engineer - UFIV

The Correct Answer is C. ### Explanation for Option C (3) The illustration (MO-0144, which depicts a common type of jerk pump fuel injection system) shows a fuel pump plunger that controls both the start and end of injection using a helix (or scroll) cut into its body, interacting with inlet/spill ports in the barrel. Position **3** corresponds to the end of fuel injection. This occurs when the upper edge of the helix/scroll aligns with and uncovers the spill port (or relief port). Once the spill port is uncovered, the high-pressure fuel trapped above the plunger rushes out through the port and returns to the suction gallery (or fuel tank). Because the pressure immediately drops to zero, the delivery valve closes, and injection into the engine cylinder ceases. ### Explanation for Incorrect Options * **A) 1:** Position 1 represents the plunger at or near the bottom of its stroke (Bottom Dead Center) or during the suction phase. Both the inlet and spill ports are open, allowing the fuel gallery to fill the space above the plunger. No injection is occurring. * **B) 2:** Position 2 represents the point where fuel injection begins. The plunger has moved upward, and its effective top edge has just covered both the inlet and spill ports (the "effective stroke" begins here). From this point until the spill port is uncovered by the helix, the fuel is pressurized and delivered to the injector. * **D) 4:** Position 4 represents the plunger near the top of its stroke (Top Dead Center) and well past the point where injection ended (position 3). The spill port has been uncovered for some time, and the pressure relief has occurred. This position merely signifies the end of the plunger's upward travel (or the end of the overall pump stroke).