🔍 Key Concepts

• Study how a unit injector works: the cam and tappet create pressure, but a separate part controls when injection stops by uncovering or blocking spill/ports. • Distinguish between parts that only create motion/pressure (like cams and plungers) and the part that actually meters and cuts off the fuel flow. • Trace the path from the cam (bottom) up to the injector tip (top) and find the component that varies the effective stroke of the plunger to end injection.

💭 Think About

• Which labeled part is directly rotated or positioned by the fuel control/governor linkage to change how long injection lasts? • Looking at letters C, H, I, and K, which one actually changes the point at which high‑pressure fuel is released (spilled off) so delivery to the cylinder stops? • Is the cam itself terminating injection, or is there a part attached to/around the plunger that opens a spill port and drops pressure so the nozzle closes?

✅ Before You Answer

• Be sure you can follow the high‑pressure fuel path from the plunger to the nozzle and see where that path is suddenly opened to spill fuel. • Confirm which component is linked to the fuel rack or control lever rather than being fixed in shape like the cam or simple rocker arms. • Verify that the part you choose is the one that actually ends pressure at the nozzle (causing the needle to close), not just one that starts the plunger moving.