Mixture Control Solenoid

The fuel control system is primarily an emission control system, designed to maintain an ideal air/fuel ratio of 14.7:1 under most operating conditions. Control system uses a mixture control solenoid to constantly adjust air/fuel mixture. When the ideal ratio is maintained, the 3-way catalytic converter can control carbon monoxide (CO), hydrocarbon (HC) and oxides of nitrogen (NOx) emissions.

Air/fuel ratio is judged to be rich when voltage produced by O2 sensor is greater than .5 volt. As a result, control unit energizes mixture control solenoid to pass a greater quantity of air into carburetor. This additional air leans air/fuel mixture. Air/fuel ratio is judged to be lean when voltage produced by O2 sensor is less than .5 volt. As a result, control unit de-energizes mixture control solenoid to pass less air into carburetor. The elimination of air enrichens air/fuel mixture.

This energizing and de-energizing process takes place 16 times per second. The factor which determines whether the carburetor air/fuel mixture is leaned or enrichened is the time which the solenoid is energized and de-energized during each of these 16 cycles.