Ignition System: Description and Operation

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OVERALL DESCRIPTION
The ignition timing advance and spark duration characteristics are controlled by the engine control unit (ECU).
This engine uses a Direct Ignition System. It employes a multiple power transistor pack and ignition coil pack. There is no distributor, cap, or rotor.

Refer to COMPUTERIZED ENGINE CONTROLS for further information on the control of the ignition system.
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.
It accomplishes this in the following manner.
When the ignition key is turned on, battery Voltage is supplied to the positive side of the primary and secondary windings of the ignition coils through the ignition coil relay. As the engine begins to turn, the crank angle sensor determines the engine rpm and camshaft position and sends this information to the ECU. Based upon a determination made by several sensors as to the proper ignition timing requirements, the ECU then supplies a pulsed ground signal to the base of the power transistors. The power transistors cut the Voltage to the primary windings in the ignition coils. 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 (approximately 20,000 Volts) flows out of the coils and into the spark plug. The Voltage then jumps the gap at the spark plug electrode completing the path to ground, igniting the fuel mixture.

SYSTEM COMPONENTS
The ignition system consists of these components:
Battery
Coil Pack
Ignition Relay
Power Transistor
Spark Plugs

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:
Acceleration
Hot engine operation
Idle
Starting
Warm-up