Ignition System: Description and Operation

PURPOSE
To produce a spark that will ignite the air/fuel mixture within an engine's cylinders, ignition systems generate high voltage and direct it to spark plugs at each cylinder. Voltage must be high enough to jump the spark plug gap under compression and it must be supplied at the correct time under a wide range of operating conditions.

OPERATION
When the ignition switch is turned on battery voltage is applied to the ignition coil primary winding.
As the distributor shaft rotates the signals from the crankshaft position sensor and camshaft position sensor are sent to the engine control module.
These signals activate the ignition power transistor which causes the ignition coil primary voltage to flow through the negative terminal of the coil, through the power transistor and to ground being interrupted repeatedly.
The ignition system induces high voltage in the secondary winding of the ignition coil. From the ignition coil the secondary winding current flows through the coil, coil wire, distributor cap, rotor, spark plug wires to the spark plugs igniting the fuel/air mixture in each cylinder in firing order.


COMPONENTS
- Spark plugs
- Ignition coil.
- Camshaft driven distributor with integral crankshaft position sensor and camshaft position sensor.
- Power transistor.
- Distributor cap and high tension wiring for distributing high voltage to the spark plugs.

CRANKSHAFT POSITION AND CAMSHAFT POSITION SENSORS
The crankshaft position sensor and camshaft position sensors are photo-diode types that provide the engine control module with signals regarding engine rpm and #1 cylinder top dead center (camshaft position). Together with other inputs, the engine control module calculates ignition timing over the range of vehicle operating conditions.

POWER TRANSISTOR
An engine control module controlled power transistor is used as a switch to regulate current flow through the coil primary circuit. Each time current flow is interrupted, high voltage is induced to fire the spark plugs. Except for the initial setting, timing is determined by the engine control module.

SECONDARY IGNITION COMPONENTS
A distributor cap, rotor and high tension wires are used to direct high voltage from the coil to each spark plug at the appropriate time as calculated by the engine control module.