Synchronisation of the crankshaft and camshaft is necessary in order to ensure the engine start procedure functions correctly.
The crankshaft sensor registers the crankshaft position. The control unit’s internal parameters correlate this information with the various top dead centre positions.
The level of the signal from the camshaft sensor distinguishes between gas-expulsion TDC and injection TDC.
By comparing these two signals the control unit can actuate the correct injector to inject fuel into the cylinder.
Injection is then repeated in the sequence corresponding to the engine’s firing order, namely cylinders 1-5-3-6-2-4 (M57).
The M67 sequence for fuel injection is 1-5-4-8-6-3-7-2.
Fuel injection ceases if no valid edge change is detected in the signal from the camshaft sensor after two complete engine revolutions (for example because no camshaft sensor installed, static level was coincidental).