🔍 Key Concepts

• Study how the upper port, lower port, and recessed/helix area line up with the barrel in each vertical position 1–4 in Figure A. • Remember that injection begins when the spill (horizontal) port is closed and high pressure can build above the plunger. • Injection ends when a port is uncovered again, allowing fuel to spill off and pressure at the nozzle to drop.

💭 Think About

• In Figure A, at which numbered position is the plunger’s recessed/helix area first opening a passage back to the port so pressure can no longer be maintained at the nozzle? • Compare positions 2, 3, and 4: in which one is there a clear flow path from the high‑pressure area above the plunger back to a port, so the pump can no longer deliver fuel? • Ask yourself: if the plunger kept moving downward past the end‑of‑injection point, would that change the fact that the ports are already uncovered and pressure has collapsed?

✅ Before You Answer

• Identify in each position whether the horizontal drilling/port is covered or uncovered by solid plunger metal. • Confirm where the recessed/helix area connects the high‑pressure side to the port – that position corresponds to the end of injection. • Make sure you are looking only at Figure A (vertical plunger travel) and not the rotational positions in Figure B when choosing among 1–4.