SAAB WIS ONLINE

Starting ignition timing

Starting ignition timing


From the time the engine is stationary until it reaches the requested idling speed, starting ignition timing is active.

The ignition timing is normally 10° BTDC but is retarded when the temperature of the intake air exceeds 4 °C. When the temperature of the intake air reaches 100 °C, the ignition advance is 3° BTDC. The reason for retarding the ignition when the air temperature rises is that the combustion speed then increases as well.

On starting, the control module triggers each cylinder with 200 Hz for 60 crankshaft degrees, whereby a multiple spark is generated. As the engine speed exceeds 450 rpm, this frequency will be increased to 330 Hz. The function is terminated when the engine speed exceeds 650 rpm. If the engine speed drops below 450 rpm again, the function will be reactivated, provided the coolant temperature is below -10°C.

The aim is to ensure ignition under unfavourable starting conditions and to prevent the engine dying after starting.