🔍 Key Concepts

• Relationship between the camshaft, push rod, and rocker arm in producing mechanical motion and pressure in a unit injector • Role of the electronically controlled solenoid in starting and stopping fuel flow (controlling injection event) • Difference between pressurization, timing, and metering of fuel in modern electronic unit injectors

💭 Think About

• From the illustration, trace the force path from the camshaft up to the injector body. Which part is actually capable of squeezing (pressurizing) the fuel? • Think about what an electronic solenoid can do quickly and precisely in an engine cycle. Is it better suited to create high mechanical pressure, or to open/close a small passage at precise times and durations? • If the rocker arm motion is fixed by the cam profile, what aspects of injection can still be varied electronically without changing the cam?

✅ Before You Answer

• Identify which component directly moves the injector plunger to create high fuel pressure. • Decide which device (mechanical or electronic) can most accurately control start and end of injection (timing) and quantity of fuel (metering). • Eliminate any option that asks the solenoid to do the heavy mechanical work of pressurizing the fuel instead of the cam/rocker/push rod train.