Feedback System

Fig. 2 Oxygen sensor installation:

The mixture ratio feedback system includes an oxygen sensor, ECM and carburetor mounted Mixture Control (MC), solenoid. The feedback system provides precise control of engine air/fuel mixture ratio in order to allow proper operation of the three-way catalyst while maintaining acceptable driveability and fuel economy. The ECM monitors exhaust gas content, and thereby air/fuel mixtures entering the engine, through the exhaust manifold mounted oxygen sensor, Fig. 2. The ECM cycles the MC solenoid on and off at a constant rate of 16 times per second, and controls air/fuel mixtures by varying the amount of solenoid ``On'' time (dwell period) per cycle. The MC solenoid controls the main air bleed in the carburetor primary metering circuit, opening the bleed when energized and closing the air bleed when de-energized.