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Ignition system, knock regulation

Ignition system, knock regulation


The Saab Trionic ignition system is a capacitive ignition system and consists of four ignition coils and electronics built into the ignition discharge module. The ignition coils are controlled by the electronics in the ignition discharge module, which in turn are regulated via low-level outputs from the ECM.

When the engine is cranked, the ignition system produces a spark on two spark plugs simultaneously, 1 and 4 or 2 and 3, for a number of consecutive complete combustion processes. Following this, on the basis of the ionization current flowing through the spark plugs and signals from the crankshaft position sensor, the system has sufficiently reliable information to synchronize spark generation and fuel injection to the correct cylinder.

To improve starting performance when the engine temperature is below 0°C, the ignition system generates a large number of sparks in quick succession (multispark function), while the starter motor is engaged (10°BTDC - 20°ATDC).

The crankshaft position sensor consists of an inductive sensor mounted in the crankcase wall of the engine. The rotor is a perforated disc with 58 ribs, which is mounted on the rear counterweight of the crankshaft.

Ignition timing

The ignition timing is calculated by the control module chiefly on the basis of the following information:


• engine load

• engine speed

• any knocking

• throttle position (idling only)



The control module determines whether knocking is occurring in any of the cylinders by analyzing the ionization currents passing through the spark plugs. If knocking occurs, ignition is retarded. In the event of major ignition regtardation or high boost pressure, a richer fuel/air mixture is also produced. The boost pressure is reduced as a final step.