Ignition System: Description and Operation

PURPOSE

The purpose of the Ignition System is to provide a high voltage spark to each cylinder at the optimum time and with sufficient power to promote complete burning of the fuel/air charge.

OPERATION

The Engine Control Module (ECM) has, stored within it, complicated "ignition maps" to determine the correct ignition timing depending on engine speed and intake manifold vacuum pressure information calculated from the various input devices.
This system, not dependent on a governor or vacuum diaphragm, is capable of setting the timing with more accuracy than a conventional system with governors or diaphragms.
With the ignition switch in the ON or START position, voltage is applied to the Ignition Coil and the Ignition Control Module (ICM). As the distributor shaft turns, the ICM acts as a switch, controlled by the Engine Control Module (ECM), to control current flow through the primary winding of the ignition coil. When the current flow stops, a high-voltage current is induced in the secondary winding of the ignition coil. This high-voltage current flows through the distributor cap and rotor to the proper spark plug , where it must jump a gap to reach engine ground. When the voltage pulse jumps the gap to ground, it creates a spark (ignition spark) strong enough to ignite the air/fuel mixture in the combustion chamber.