🔍 Key Concepts

• Fuel injection pump discharge (delivery) valve function – what it normally does during and after injection • Effective stroke of the plunger – the part of plunger travel that actually delivers high‑pressure fuel to the injector • Effect of leakage / loss of pressure in the high‑pressure line on when injection starts and stops

💭 Think About

• When fuel leaks past discharge valve F, what happens to the pressure in the high‑pressure line during the plunger’s upward stroke? Does it build up faster, slower, or stay the same? • Think about when injection STOPS: is it controlled by the pump plunger position only, or also by how quickly pressure drops off in the high‑pressure line after the plunger uncovers the spill port? • If pressure in the line bleeds off between pumping strokes, does the plunger need to travel MORE or LESS distance on the next stroke before the injector opens?

✅ Before You Answer

• Identify clearly on the illustration which volume is the high‑pressure fuel space/line and how it connects to discharge valve F and the injector line. • Review the definition of effective plunger stroke: from the point where fuel delivery (injection) begins to the point where injection ends. • Ask yourself: with leakage at F, will injection begin earlier or later in the plunger’s upward travel, and will the total effective stroke be greater or smaller than normal?