Ignition System: Description and Operation

Ignition System Circuits:

PURPOSE
The ignition system turns electrical energy from the battery (12 volts DC) into a high voltage electrical pulse. This pulse is routed to the appropriate spark plug and once there, must possess sufficient voltage to jump the spark plug's gap, which extends into the combustion chamber, and ignite the air/fuel mixture. The ignition system must deliver the energy pulse at precisely the right instant at a rate of up to 300 times per second.

OPERATION
The engine control module (ECM) is programmed with data for optimum ignition timing under all operating conditions. Using data provided by sensors which monitor various engine functions (rpm, intake air volume, engine temperature, etc.), the ECM triggers the spark at precisely the right instant.

The ECM monitors the engine condition by signals from each sensor, calculates the ignition timing and sends an ignition signal to the igniter. The high voltage discharge from the ignition coil is distributed to each spark plug, in the appropriate order, through the distributor rotor, cap and cables.

Listed below are various components of the ignition system and a brief description of their function.





Igniter
The igniter temporarily interrupts the primary current with the ignition signal (IGT signal) from the ECM and generates sparks at the spark plug, Also, as a fail-safe measure, when ignition occurs an ignition confirmation signal (IGF signal) is sent to the ECM.

Ignition coil
The ignition coil uses a closed core coil with the primary coil wrapped around the core and the secondary coil wrapped around the primary coil. This allows the generation of a high voltage sufficient to cause a spark to jump across the spark plug gap.

Distributor
This distributes high voltage to the ignition cable of each cylinder in the specified ignition order.

Pickup coils
The NE coil detects the crankshaft position (rpm), G1 and G2 coils detect the camshaft position (TDC).