TDI and timing

[dalek]

Dumb question: how does the TDI pump know when it is time to open and spill the fuel? Is it the ECU or the mechanically though the engine (which talks to belt and pump)?

[gigaz2]

the selenoid under the pump controls the timing plunger, that retards or advances the roller ring
thats the dynamic timing, its ecu controlled.

as fuel pressure increases over the injector set pressure they open and atomize fuel into the chamber

the number 3 injector has a sensor to know when the needle lifts, the ecu calculates how much time has passed from TDC (via the flywheel sensor) and computes the REAL timing, then changes the pump timing as required. its a loop