Ignition System: Description and Operation

Fig. 1 Schematic view of American Motors solid state ignition system less electronic feedback system:

Fig. 2 Schematic view of American Motors solid state ignition system with electronic feedback system:

This ignition system, Figs. 1 & 2, is used on 1984-87 vehicles. The solid state ignition system consists of the ignition switch, electronic ignition control unit, ignition coil, primary resistance wire and bypass, distributor, spark plugs and on most 1982-87 models with electronic feedback system, an electronic spark retard.
The electronic ignition control unit is a solid state, moisture resistant module. The component parts are sealed in a potting material to resist vibration and environmental conditions. The control unit is incorporated with reverse polarity protection and transient voltage protection.
The distributor incorporates a sensor and trigger wheel. Current flowing through the ignition coil creates a magnetic field in the primary windings. When the circuit is opened, the magnetic field collapses and induces a high voltage in the coil secondary windings. This circuit is electronically controlled by the electronic ignition control unit. The distributor sensor and trigger wheel provide the signal to operate the control unit. The trigger wheel is mounted on the distributor shaft and has one tooth for each cylinder. The sensor, a coil of fine wire mounted to a permanent magnet, develops an electromagnetic force that is sensitive to the presence of ferrous metal. The sensor detects the trigger wheel teeth as the teeth pass the sensor. When a trigger wheel tooth approaches the pole piece of the sensor, it reduces the reluctance of the magnetic field, increasing field strength. Field strength decreases as the tooth moves away from the pole piece. This increase and decrease of field strength generates an alternating current which is interpreted by the electronic ignition control unit. The control unit then opens and closes the ignition coil primary circuit.
Since there are no contacting surfaces and no wear occurs, dwell angle requires no adjustment. The dwell angle is electronically controlled by the electronic ignition control unit. When the coil circuit isswitched open, an electronic timer in the control unit keeps the circuit open only long enough for the spark to discharge. Then, it automatically closes the ignition coil primary circuit.