Engine Fuel Pump Mechanics

Study Notes

Suction Action

Cranking the engine rotates the crankshaft and the master timing gear.
The Acc drive gear, meshed with the master timing gear, drives the camshaft of the High-Pressure Fuel Pump (HPFP).
Cam lobe No.3 rotates, moving away from the feed pump plunger.
The return spring of the plunger completes its tension, bringing the plunger downward.
The piston returning spring also completes its tension, pulling the piston downward.
As the piston descends, a suction effect is generated at the top of the piston.
This suction opens the one-way inlet check valve, allowing fuel to be drawn from the fuel tank into the feed pump.

Ejection Action

The driving action remains consistent; however, cam lobe No.3 positions itself under the plunger.
As cam lobe No.3 comes under the plunger, the plunger moves upward.
The plunger returning spring compresses in response to the upward movement.
The piston, located atop the plunger, also moves upward, compressing its returning spring.
The upward motion of the piston exerts pressure on the fuel, leading to the opening of the one-way outlet check valve.
Fuel is then sent to the HPFP through a fine fuel filter.

Back Pressure Action

This action assumes that the HPFP requires no fuel.
Following the suction action, as the piston moves upward for ejection, its spring compresses.
The absence of fuel demand results in pressure being exerted on the fuel.
Fuel enters beneath the piston via a bypass and settles there.
The piston remains in a half-cocked position until fuel demand increases.

Description

This quiz covers the mechanics of the High-Pressure Fuel Pump (HPFP) in automotive engines, focusing on the suction and ejection actions. It details how engine cranking and camshaft movement generate suction to draw fuel and the mechanisms involved in pushing the fuel into the engine system.