Ignition System: Description and Operation

DESCRIPTION AND OPERATION
The Multiport Fuel Injection System consists of sensors which detect the engine conditions, the ENGINE CONTROL MODULE (ECM) which controls the system based on signals from these sensors, and actuators which operate under the control of the ECM.
The ECM carries out activities such as fuel injection control, idle air control, and ignition timing control. In addition, the ECM is equipped with several diagnostic test modes which simplify troubleshooting when a problem develops.

IGNITION TIMING CONTROL
The ignition power transistor located in the ignition primary circuit turns ON and OFF to control the primary current flow to the ignition coil. This controls the ignition timing to provide the optimum ignition timing with respect to the engine operating conditions. The ignition timing is determined by the ECM from the engine speed, intake air volume, engine coolant temperature, and atmospheric pressure.



GENERAL INFORMATION
Interruption of the primary current flowing in the primary side of the ignition coil generates high voltage in the secondary side of the ignition coil. The high voltage thus generated is directed by the distributor to the applicable spark plug. The engine firing order is 1 - 3 - 4 - 2 cylinders.
On application of high voltage, the spark plug generates a spark to ignite the compressed air fuel mixture in the combustion chamber.
The engine control module makes and breaks the primary current of the ignition coil to regulate the ignition timing.
The engine control module detects the crankshaft position by the crankshaft position sensor installed at the front end of the crankshaft to provide ignition at the most appropriate timing for the engine operating condition.
When the engine is cold, the ignition timing is slightly advanced to provide optimum performance to the operating condition.




SYSTEM DIAGRAM

OPERATION
- Turn ignition switch to "ON" position, and battery positive voltage will be applied to primary winding of ignition coil (incorporated into the distributor).
- When the crankshaft position sensor signal is input to engine control module, ON-OFF control of ignition power transistor is performed by engine control module.
- When ignition power transistor is turned on, current flows from the ignition coil (primary winding) to ground through the ignition power transistor.
- When the ignition power transistor is turned off, high voltage is generated in the primary winding of ignition coil which induces even higher voltage in the secondary winding, causing a spark at the spark plug(s).