Ignition System: Description and Operation

The ignition system consists of an ignition coil, ignition module, distributor, spark plugs, and spark plug wires. Ignition spark timing correction is achieved by centrifugal advance weights, a vacuum control diaphragm, and the ignition module. The ignition timing is modified by the Electronic Control Assembly (ECA). Based on inputs from the Barometric Pressure Sensor (BP), at altitudes of 3,280 ft. (1000 m) or higher, the ECA will signal the ignition module to advance ignition timing.

The crankshaft angular position is sensed by a pulse generator, consisting of a four-lobed armature mounted on the shaft and rotating in the field of a two-pole permanent magnet stator. As the armature lobes pass the stator poles, magnetic pulses are generated, which induce weak currents in a pickup coil, which is part of an electronic ignition module. The module controls the current through the ignition coil primary winding. The module turns the current on between firing points to build up a magnetic field around the coil windings. When a signal is received from the pulse generator and pickup coil the current is turned off. Once the current is turned off, the field collapses and a high voltage pulse over 20,000 volts is induced in the coil secondary winding. The pulse is transmitted to the central terminal in the distributor cap, and through the rotor to the distributor cap terminal for the spark plug whose turn it is to fire. At the plug electrodes, in the combustion chamber, the high voltage arcs to ground, to ignite the compressed air/fuel charge in the cylinder.