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. This vehicle uses an Engine Control Module (ECM) controlled electronic direct ignition system. Components include:

^ 2 Ignition coils.
^ Cam and crank angle sensors.
^ Ignitor (power transistor).

CRANK/CAM ANGLE SENSORS
The crank/cam angle sensors are mounted in the distributor that provide the ECM with signals regarding engine rpm and #1 cylinder TDC (camshaft position). Together with other inputs, the ECM calculates ignition timing over the range of vehicle operating conditions.

IGNITOR
An ECM controlled ignitor 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 ECM.

SECONDARY IGNITION COMPONENTS
Secondary voltage is supplied by two ignition coils, resistor cables and resistor spark plugs. Each coil supplies voltage to two cylinders. Coil #1 supplies voltage to cylinders #1 & #2, coil #2 supplies voltage to cylinders #3 & #4 simultaneously; one cylinder on firing stroke and one on exhaust stroke.