Turbo

Fig. 23 Fuel Injection System Component I.D.:

The basic ignition timing is determined by:
Engine speed
Engine load
An ignition map 256 points (16 engine load, and 16 engine speed points) is programmed into the control unit memory. Depending on these two conditions, the ignition timing will normally be somewhere within the map area.
The benefit of this system is that the ignition timing will always be at the most optimum point for all operating conditions.
If a cylinder develops ignition knock (detonation or "pinging"), the control unit will detect this through the knock sensor. The control unit will then retard the ignition timing until the knocking is stopped. Once the knocking has stopped, the timing will be advanced back towards its normal value.
To prevent erroneous readings, the knock sensor signal will only be processed when the engine is in the operating range where ignition knock can occur. These are when:
Engine coolant temperature is above 70°C (158°F)
Intake manifold pressure is above 0.7 bar (from 7 in. of vacuum to full boost)
Idle switch open