Microprocessor Control Unit (MCU)
This is the "brain" of the system. It is the central component of the control loop. It constantly monitors EGO signals, throttle angle and coolant temperature. The determined response is sent out to the vacuum solenoid/regulator, which supplies vacuum signal to the fuel metering rod to obtain the proper air/fuel ratio required for optimum operation of the catalytic converter. The MCU also has a time mechanism which varies the length of time required for a change in air/fuel ratio based on engine RPM.
NOTE:
The electronic control unit sends a constantly cycling voltage to the solenoid regulator. Control is accomplished by varying the duration of the voltage within a given time. A "short duty cycle" means the electronic control is sending voltage less than half the time.