Closed Loop
When all input data and engine operation meet programmed criteria, the CEC system goes into closed loop operation. In this mode, oxygen sensor input signals are accepted by MCU to determine proper air/fuel mixture based upon oxygen content of exhaust gases.
The MCU may also receive signals from the knock sensor and adjust ignition timing accordingly. Air injection is routed "downstream" or both "upstream" and "downstream" for various throttle positions.
NOTE:
Closed loop operation is characterized by constant movement of the metering pins. The MCU is constantly making small corrections in air/fuel ratio in an attempt to create the ideal air/fuel ratio.