Pre-Injection Phase Ends - Volkswagen 1.9-Liter TDI Owner's Manual

Pump Injection System

Pre-Injection Phase Ends

The pre-injection phase ends immediately
after the injector needle opens.
The rising pressure causes the retraction
piston to move downward, thus increasing
the volume of the high-pressure chamber.
The pressure drops momentarily as a
result, and the injector needle closes.
Roller-Type
Rocker Arm
Injection Cam
High-Pressure
Chamber
Retraction Piston
24
This ends the pre-injection phase.
The downward movement of the retraction
piston pre-loads the injector spring to a
greater extent.
To re-open the injector needle during the
subsequent main injection phase, the fuel
pressure must be greater than during the
pre-injection phase.
Solenoid
Valve Needle
Piston Spring
Pump Piston
Pump/Injector
Solenoid Valve
Fuel Return Line
Fuel Supply Line
Injector Spring
Injector Needle
SSP209/026