Ignition System: Description and Operation

Ignition Timing Control:

The programmed ignition system (PGM-IG) consists of a distributor, ignition coil, distributor cap, distributor rotor, igniter, spark plugs, secondary ignition wires, crank angle sensor, and TDC sensor.
Battery voltage is supplied to the positive side of the ignition coil by the ignition switch. As the crank rotor (reluctor for the crank angle sensor) inside the distributor rotates it collapses a magnetic field surrounding the crank angle sensor. The collapse of this field produces a voltage pulse in the crank angle sensor windings. The pulse is transmitted to the power switching transistor located inside the igniter unit. The pulse of the power switching transistor interrupts current flow through the primary circuit. This interruption induces high voltage in the secondary coil. The high voltage travels through the coil wire to the distributor cap where it is transferred, by the distributor rotor, to the specified secondary ignition wire. Finally the high voltage reaches a spark plug where it jumps a specified gap and ignites the air/fuel mixture within the combustion chamber. The crank angle sensor and crank rotor are located inside the distributor.

Basic Control:

During normal engine operation the PGM-IG system provides maximum control of the ignition timing by utilizing a microcomputer in response to electronic signals transmitted by the TDC/CRANK sensor, throttle angle sensor, coolant temperature sensor, and MAP sensor. During cranking the ignition timing is fixed at 10° BTDC.