What are the reasons for the diesel high-pressure fuel injection pump not delivering oil?

[StMia]

Diesel high-pressure fuel injection pump not delivering oil is a problem with the high-pressure fuel pump, where the fuel supply rack of the high-pressure fuel pump plunger is stuck in the fuel cutoff (shutdown) position. Working principle: In the last 1/3 segment of the pump piston stroke, the fuel pressure regulating valve is energized, keeping the intake valve open during the initial upward movement of the pump piston to allow fuel return. Fuel return stroke: The intake valve remains open during the initial upward movement of the pump piston, and excess fuel is pushed back to the low-pressure side by the pump piston. The pressure damper's role is to absorb pressure fluctuations generated during this process. Fuel pumping stroke: At the beginning of the fuel pumping stroke, the fuel pressure regulating valve is de-energized, causing the intake valve to close under the combined action of the rising pressure in the pump chamber and the closing spring inside the valve.