Ignition System: Description and Operation

System Description:

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.

This vehicle utilizes an ECU controlled Electronic Spark Advance (ESA) System. Components include:

^ Ignition coil.
^ Camshaft driven distributor with crank angle sensor.
^ Igniter.
^ Distributor cap and high tension wiring for distributing high voltage to the spark plugs.

The crank angle sensor generates two signals utilized by the ECU in its calculations for ignition timing and other outputs. The sensor is a magnetic pick-up type with reluctor (signal rotor) turned by the distributor shaft. The "Ne" signal detects crank angle at 30° intervals and is utilized by the ECU to determine engine rpm. The "G1" and "G2" signals detect #1 and #4 cylinders TDC and are utilized by the ECU to determine fuel injection and ignition timing.

An ECU controlled igniter 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 ECU. A knock control system consisting of a knock sensor and knock control unit signal the ECU to retard timing when detonation is detected.

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.