🔍 Key Concepts

• Port-and-helix fuel injection pump operation (how fuel starts and stops flowing) • Difference between total pump stroke and effective pump stroke • What the helix on the plunger actually controls in the timing/control of injection

💭 Think About

• Ask yourself: what event in this pump design actually ends fuel injection—reaching the top of the stroke, or uncovering a port? • Which part(s) of the plunger motion really move fuel into the cylinder at high pressure, and which part(s) are just mechanical movement without injection? • How would changing the plunger helix angle affect when the spill port is uncovered during the stroke?

✅ Before You Answer

• Be clear on the definition of effective pump stroke versus total pump stroke • Visualize when pressure is high enough to open the injector nozzle and when it drops off again • Confirm which factor directly sets the time interval during which fuel is actually being injected, not just being pressurized or moved in the pump