🔍 Key Concepts

• Control rack moves a gear that rotates the plunger with the helical groove • Rotating the plunger changes when the spill port is uncovered during the stroke • Cam lift (up‑and‑down motion) and injection timing for each cycle stay essentially the same

💭 Think About

• Look at how the rack teeth mesh with the gear on the plunger: what does changing the plunger’s angular position actually change inside the barrel? • If the cam lift and pump stroke do not change, what part of the injection event can still be varied by rotating the helical plunger? • Does the rack movement directly act on pressure, or does it change how long high pressure is maintained before fuel is spilled back?

✅ Before You Answer

• Identify on the illustration where the helical groove meets the spill port and how rotation would change that relationship. • Decide whether the duration of effective stroke (before spill) or the basic cycle itself is being altered. • Confirm that the fuel pump delivery pressure is primarily a result of cam lift and plunger area, not rack position.