: Driven by the engine's camshaft, the plunger moves upward. Once it covers the barrel ports, the trapped fuel begins to compress.
If you'd like to explore a specific part of the system further, I can help you with: A deeper look at the and how it meters fuel. Comparing mechanical governors vs. electronic ECU control. Fuel Injection pump working principle - Animation
: To stop injection, a helical groove on the plunger eventually uncovers a spill port . This allows pressurized fuel to "spill" back into the lower-pressure gallery, causing the delivery valve to close instantly. : Driven by the engine's camshaft, the plunger moves upward