Fuel/Timing Control Unit

The fuel/timing control unit is located under the instrument panel on right side of passenger compartment. It receives the information pulses from the various sensors. It then determines the optimum ignition timing and fuel mixture for all engine operating conditions, actuating the ignition control unit and frequency valve.

When the throttle valve is closed, ignition timing is determined by the idle stabilizer function in the control unit. This function switches on when engine speed is below 820 RPM. Between 720 and 820 RPM, ignition timing is advanced from 6° to 26° BTDC. The idle stabilizer advances timing to 26° BTDC when engine speed is between 600 and 720 RPM.

Below 600 RPM, the idle stabilizer does not function. Timing is retarded to ensure easy starting. During deceleration, basic timing is advanced depending upon engine RPM, to ensure low exhaust emissions and to prevent backfiring.

When the throttle valve is opened, ignition timing is determined by engine speed, intake manifold pressure, and coolant temperature.

Above 14.5 psi (1.02 kg/cm² ), ignition timing is also influenced by intake air temperature. On deceleration, ignition timing is determined by engine speed characteristic line, programmed into the control unit memory. Closed loop control is not possible until coolant temperature is above 90°F (32°C).

Until coolant temperature rises above 90°F (32°C), and oxygen sensor warms up, duty cycle is regulated between 42-65%. The fuel/timing control unit works in conjunction with a frequency valve to vary the amount of fuel delivered to the engine.