Ignition System: Description and Operation

Fig. 1 American Motors (Motorcraft) Solid State Ignition (SSI) System. 1983 6-258 & 1984-85 4-150 Engines:

Fig. 2 American Motors (Motorcraft) Solid State Ignition (SSI) System. 1984-87 6-258 engines:

Fig. 3 American Motors (Motorcraft) Solid State Ignition (SSI) System. V8-360 engines:

Fig. 4 Exploded view of distributor assembly. 6-258 shown, 4-150 & V8-360 similar:

The solid state ignition system, Figs. 1 through 3, consist of an ignition switch, electronic control unit, ignition coil, primary resistance wire and bypass, distributor, spark plugs and on models with electronic feedback system, an electronic spark retard.
The electronic ignition control unit is a solid state , moisture resistant module. Internal components are sealed in a potting material to resist environmental conditions and vibration. Reverse polarity and transient voltage protection are incorporated into the module.
The distributor incorporates, Fig. 4, 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 secondary windings. This current is electrically controlled by the electronic ignition control unit. The signal to operate the control unit is provided by the distributor sensor and trigger wheel. The trigger wheel is mounted ion 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 a ferrous metal. When a trigger wheel tooth approaches the sensor pole piece, reluctance of the magnetic field is reduced, increasing field strength. As the tooth moves away from the sensor pole piece, field strength will decrease. This increase and decrease of field strength produces and alternating current which is interpreted by the electronic ignition control unit. The control unit then opens and closes the ignition primary circuit.
Since there are no contacting surfaces, no wear occurs and dwell angle requires no adjustment. Dwell angle is electronically controlled by the electronic ignition control unit. When the coil circuit is switched open, an electronic timer in the control unit keeps the circuit open only long enough for the spark to discharge. After the spark discharge, the electronic control unit will automatically close the ignition primary circuit.