Engine Ignition: Operation

Four ignition coils are fitted directly to the spark plugs and are located in the center of the camshaft cover. The two inner coils for cylinders 2 and 3 are secured to the camshaft cover with screws and the two outer coils for cylinders 1 and 4 are secured with two studs and nuts. Each ignition coil has a three pin connector, which incorporates the following connections:

• A power supply from the BJB by the ECM relay, through a 15A fuse.
• A power ground which allows the secondary winding to connect to ground.
• A signal connection from the ECM, to control the ignition coil power stage switching (to open and close the primary circuit).

The ECM sends a separate signal to each ignition coil to trigger the power stage switching, to close and open the primary current. The 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 ECM calculates the ignition timing for individual cylinders from the following inputs:

• Engine speed from crankshaft position (CKP) sensor.
• Camshaft position from exhaust and intake camshaft position (CMP) sensors.
• Engine load.
• Engine temperature.
• The knock control function.
• The shift control function.
• The idle speed control function.