Ignition System: Description and Operation

PURPOSE
The automotive ignition system is designed to:
^ Increase battery voltage to 20,000 volts or more.
^ Distribute voltage to the spark plugs.
^ Ignite the air fuel mixture.

OPERATION
When the ignition key is turned on, battery voltage is supplied to the positive side of the ignition coil. As the engine begins to turn, the crank angle sensor determines the engine rpm and camshaft position and sends this information to the ECM.

The ECM takes the information, based upon a map programmed into the ROM memory, supplies a pulsed ground signal to the base of the power transistor. The power transistor cuts the voltage to the primary windings in the ignition coil. This causes the magnetic field surrounding the primary windings to collapse and a voltage surge is created in the secondary windings of the ignition coil.

High voltage flows out of the coil directly to the spark plug. Jumping the gap at the spark plug electrode completes the path to ground, igniting the fuel mixture.

For more information regarding the control factors of ignition timing, refer to COMPUTERS AND CONTROL SYSTEMS.

SYSTEM COMPONENTS
The ignition system consists of these components:
^ Battery
^ Ignition Relay
^ Power Transistor
^ Coils (6)
^ Spark Plugs

Ignition Timing Control System:

CONTROL FACTORS
The ignition timing is controlled by the ECU to help maintain the best air fuel mixture under all operating conditions.
The ECU uses several sensors to calculate the amount of timing based on a map stored in its memory. The ECU varies the timing during:
^ Starting
^ Warm up
^ Idle
^ Low battery voltage
^ Engine detonation
^ Hot engine operation
^ Acceleration