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. Various systems of controlling spark generation and timing have been devised. These range from completely mechanical to ECU activated electronic to distributorless.
Operation
^ When the ignition switch is turned to the "ON" position, battery voltage is applied to the primary winding of the ignition coil.
^ When crankshaft position sensor signal is input to Engine Control Module (ECM), the ECM supplies a ground path for the [1][2]ignition power transistors one by one.
^ When an [1][2]ignition power transistor is turned on, current flows from ignition coil--primary winding--through the power transistor to ground.
Interruption of current flowing in the primary windings generates high voltage in the secondary windings. The high voltage thus generated is directed by the distributor to the applicable spark plug. 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 detects the crankshaft position by the crankshaft position sensor incorporated in the distributor to provide ignition at the most appropriate timing for the engine operating condition.
When the engine is cold or operated at a high altitude, the ignition timing is slightly advanced to provide optimum performance to the operating condition.
Components
This vehicle uses an ECU controlled electronic ignition system. Components include:
1. Ignition coil.
2. Camshaft driven distributor with integral crank angle and camshaft sensor.
3. Power Transistor.
4. Distributor cap and high tension wiring for distributing high voltage to the spark plugs.
Crank/Cam Angle Sensors
The crank/cam angle sensors are photo-diode types that provide the ECU with signals regarding engine rpm and #1 cylinder TDC (camshaft position). Together with other inputs, the ECU calculates ignition timing over the range of vehicle operating conditions.
The ECU regulates 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 ECU.
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 ECU.