Not sure how relevant this is ---- but the injector/engine timing is produced from 2 sensors. Number 1 injector has a sensor built into the body of it and is for tdc timing on no1 piston. The 2nd sensor is on the top of the gearbox housing looking down onto the flywheel. It is down the back of the bulkhead. Sometimes it is slanged the 'knock sensor'
No, this is not a knock sensor. This is the TDC sensor, or Crank Postion Sensor (CPS) On early TDi's it was mounted on the timing gear case, on all later ones, it is on the bell housing. It is inductive and picks up on the teeth machined in the flywheel. There are two teeth missing about 90 deg *before* TDC- so the ECU has time to compute...
The ECU has a set of figures for timing advance stored in its memory, which vary according to revs, throttle position and load. Measuring timing advance off load is only half the story.
The ECU controls the timing via the timing control solonoid on the bottom of the Inj. Pump. The TCS is fed by a pulse width modulated square wave signal. The ECU receives feedback from when no.1 injector actually opens, and compares this with the required value. So it is an active system.
Basically for good running and emisions you want quite retarded timing off load and at low revs. As revs & load increase more advance is needed to allow time for more fuel to be injected. More fuel needs more time to inject, and has a longer burn time.
For cold running you need quite alot of advance since the fuel is slow to begin burning. This is why the TDi's sound very rattley when cold- the ecu is using alot of advance.
At high revs and load the ecu actually retards the timing again, as this keeps EGT's down so you dont melt the turbo & ex valves, and also reduces peak cylinder pressures to protect the HG.
Hope this helps.
