🔍 Key Concepts

• Plunger-type fuel injection pump basic parts and their functions • What the control rack actually moves or rotates inside the pump • How fuel quantity is controlled in small diesel injection systems (helix/plunger relationship)

💭 Think About

• Think about which part of the injection pump directly affects how much fuel is sent to the injector on each stroke. • Ask yourself: does the control rack make the plunger move farther up and down, or does it change something else about the plunger’s action? • Consider how the fuel inlet and outlet are opened/closed in a plunger pump—what changes when the rack is moved?

✅ Before You Answer

• Be clear on the difference between stroke length (up‑and‑down travel) and effective stroke that delivers fuel. • Recall that the control rack usually rotates the plunger (with a helical groove) rather than changing its vertical travel. • Eliminate any answer choice that confuses valve spring compression or port location with the main function of the control rack.