Engine Ignition: Operation

The ignition coils are supplied with electrical power from the battery via the engine control module (ECM) relay in the engine junction box (EJB). The engine control module (ECM) controls the operation of the engine control module (ECM) relay.

The engine control module (ECM) sends a separate signal to each ignition coil to trigger the power stage switching. The engine control module (ECM) calculates the dwell time from the battery voltage and engine speed, to ensure a constant energy level is produced in the secondary coil each time the power stage is switched. This ensures sufficient spark energy is available without excessive primary current flow, which avoids overheating and damage to the ignition coils.

The engine control module (ECM) calculates the ignition timing for individual cylinders from:

• Engine speed
• Camshaft position
• Engine load
• Engine temperature
• The knock control function
• The shift control function
• The idle speed control function.