Ignition System: Description and Operation

The distributor ignition system features a camshaft driven distributor which uses no centrifugal or vacuum advance. The diecast housing incorporates a Hall effect stator assembly.

Initial timing adjustments are not required unless the distributor has been moved from its factory setting or removed from the engine.

Ignition timing is controlled entirely by the Powertrain Control Module (PCM). Crankshaft position and engine rpm are read by the Crankshaft Position Sensor (CKP). This information is sent to the PCM. The PCM then signals the Ignition Control Module (ICM) to fire the ignition coil. The ICM controls the current through the ignition coil primary windings, turning the current ON between firing points to build up a magnetic field around the coil windings. Then it turns the current OFF on a signal from the PCM. Once the current is turned OFF, the field collapses and a high voltage pulse of about 28,000 volts is induced in the coil secondary winding.

This pulse is transmitted to the central terminal in the distributor cap, through the distributor rotor, to the distributor cap terminal and through the distributor to spark plug wire to the appropriate spark plug. At the spark plug electrodes in the combustion chamber, the high voltage arcs to ground and ignites the compressed air/fuel charge.

High-altitude spark advance correction is entirely electronic and does not affect the relative positions of the armature or distributor stator. This vehicle is equipped with a Barometric Pressure (BARO) sensor housed in the PCM. When barometric pressure drops below 670mm (26.4 in Hg), the PCM alters the Spark Output (SPOUT) signal to initiate high altitude spark advance operation.