Question 59Motor Plants - Assistant Engineer

The correct answer is B) rotating the plunger and position of the helix. The control rack of a unit injector regulates fuel delivery by rotating the plunger, which in turn alters the position of the helix. This changes the effective length of the plunger's stroke, thereby controlling the amount of fuel injected into the cylinder. Rotating the plunger and helix is the primary mechanism used to regulate fuel delivery in unit injectors, making B the correct choice. The other options are incorrect because they do not accurately describe the mechanism used in a unit injector. Altering spring tension (A), regulating check valve lift (C), or changing the actual plunger stroke length (D) are not the primary means of fuel delivery control in this type of system.