Ignition Control Module: Description and Operation

Fig. 55 EZL Control Unit:

The EZL ignition control unit contains a microcomputer, pressure sensor and the power output stage for control of the ignition coil. It is fitted to the left wheelhouse and is installed with heat conducting paste. The control unit receives information concerning engine speed (crankshaft position), intake manifold vacuum (load condition), engine temperature (coolant), air temperature, and full load (throttle valve switch).

Ignition Map:

The EZL control unit compares information from these inputs with ignition maps for typical load and speed ranges which are stored in the microcomputer. Ignition maps for both automatic and manual transmission equipped vehicles are stored in the EZL control unit. Map selection is dependant on the reference resistor.

The optimal ignition timing for each operating condition is determined from stored ignition "maps". The power output stage switches the primary current of the ignition coil between terminals 16 and 31 of the control unit. The EZL also supplies a TD (transistor speed) reference signal to the CIS-E control unit, tachometer, MAS control unit, and diagnostic socket. To further increase operating reliability, a data exchange circuit exists between the EZL control unit and the CIS-E control unit. Information concerning the coolant temperature, intake air temperature and the intake manifold absolute pressure is continuously compared by the control unit of each system.

During cranking and up to approx. 450 RPM, the ignition timing is controlled via the segment edges (fixed) of the flywheel. After approx. 460 RPM has been attained a transition from the fixed ignition timing to dynamic ignition timing (instantaneous, ignition map comparison) is made.

Various ignition characteristic curves are used in the warm-up range depending on the coolant temperature in order to reach the normal operating temperature as rapidly as possible. When a full load signal is received from the throttle valve switch the control unit adapts a fixed full load ignition map characteristic.

Above approximately 212°F coolant temperature or 90°F air temperature, the ignition is retarded to reduce predetonation. Values for ignition retard are combined for both coolant and air temperature to achieve total ignition correction. Timing correction values are as follows:

COOLANT TEMPERATURE
212°F => 2° ignition retard
230°F => 4° ignition retard
248°F => 5° ignition retard


AIR TEMPERATURE
90°F => 1° ignition retard
104°F => 3° ignition retard
122°F => 5° ignition retard