Ignition Control

• The ECM determines operating condition of the engine based on signals from the manifold absolute pressure sensor, engine coolant temperature sensor, intake air temperature sensor, crankshaft position sensor and other sources. The ECM then selects the ignition timing most appropriate for the condition thus determined from those stored in its memory and outputs at that timing a primary current OFF signal to the igniter to initiate ignition.
• This control uses a quick-to-response learning feature by which the data stored in the ECM memory is processed in comparison with information from various sensors and switches.
• Thus, the ECM can always perform optimum ignition timing taking into account the output, fuel efficiency, exhaust gas, and other factors for every engine operating condition.
• Ignition control during start-up

  Engine speed fluctuates during start of the engine, so the ECM cannot control the ignition timing. During that period, the ignition timing is fixed at 10° BTDC by using the 10° signal from the crankshaft position sensor.

  Fig 1: Flow Chart Of Ignition Control

  Courtesy of SUBARU OF AMERICA, INC.
• Ignition control after start of engine

From the time to receive crank angle signals indicating 180° of a turn, the ECM measures the engine speed, and by using this data it decides the dwell set timing and ignition timing according to the engine condition.

Fig 2: Ignition Temperature Graph

Courtesy of SUBARU OF AMERICA, INC.