Fuel Control System

The engine is equipped with a feedback carburetor which contains vacuum-operated fuel control actuators. The ECM, responding to inputs from the data sensors, constantly adjusts the air/fuel ratio to maintain engine performance. The ECM sends electrical signals to a vacuum control valve. The vacuum control valve converts the ECM signals to vacuum signals to operate the actuators.

The vacuum control valve consists of a vacuum regulator and a vacuum control solenoid. The regulator changes the inconsistent vacuum levels from the intake manifold into constant vacuum levels. The solenoid, controlled by the ECM, uses the vacuum from the regulator to operate the fuel control actuators.

When the ECM responds to signals received from oxygen sensor, the system is in closed loop operation. Under certain operating conditions, the ECM may ignore inputs from various data sensors and use a pre-programmed calibration control to operate the engine under that particular condition.

During cold engine starts, the vacuum control solenoid is turned off by the ECM to provide a rich mixture. Operating conditions which cause the ECM to ignore oxygen sensor signals cause the system to operate in the open loop mode.