Ignition Control Module: Description and Operation

The RX-7 distributorless system utilizes two coil and igniter assemblies located on the left side of the engine compartment. One unit fires the leading pair of spark plugs in each rotor chamber and the other fires the trailing pair.

The ignition coils are constructed using the principle of mutual induction to step up low (battery) voltage to high (ignition) voltage capable of firing the spark plugs. The coils consist of two windings of wire, primary and secondary, around a laminated iron core. When battery voltage flows through the outer, primary winding, a magnetic field is created. When current flow is stopped by the igniter interrupting the ground connection, the magnetic field collapses onto the secondary windings, producing high voltage in the secondary windings. The ratio of turns in the primary winding to turns in the secondary winding determines voltage multiplication.

The igniters are transistorized switching devices utilized to interrupt ignition coil ground connections and induce high voltage from coil secondary windings. A signal from the ECU controls igniter switching, enabling the ECU to regulate ignition timing based engine operating condition information received from various sensors.

The ECU calculates input from these devices to control ignition timing:

Intake air thermosensor (engine)
Crank angle sensor
Water thermosensor
Airflow meter
Throttle sensor
Pressure sensor
Oxygen sensor
Mileage sensor
Oil pressure switch
Neutral and clutch switches (M/T)
EC-AT control unit/inhibitor switch (A/T)
Back-up light and 5th switch
Electrical loads
A/C switch
PS pressure switch
Ignition switch ("START" position)
Test connector (for base timing adjustment)