Electronic Control Unit
The Electronic Control Unit (ECU) is the central component of the control loop. See Fig 1. It constantly monitors exhaust gas oxygen sensor, throttle angle vacuum switch and coolant temperature vacuum switch.
The determined response is sent out to the vacuum solenoid/regulator, which supplies vacuum signal to the fuel metering rod in carburetor to obtain the proper air/fuel ratio required for optimum operation of the catalytic converter.
The ECU also contains circuitry that, based on engine RPM, varies the length of time required for a change in the air/fuel ratio. The ECU sends this constantly cycling voltage to the vacuum/solenoid regulator.