Closed Loop Mode

This mode of operation occurs when none of the open loop engine operating conditions exist. In this mode, the MCU regulates the M/C solenoid to adjust the air/fuel mixture according to voltage signals from the oxygen sensor.

The oxygen sensor only measures oxygen content in the exhaust. Because of this, air leakage anywhere between the carburetor and the oxygen sensor can cause incorrect operation during the closed loop mode.

Closed loop operation is characterized by constant variation of the air/fuel mixture. This is because the MCU is forced to constantly make small changes in order to maintain an optimum air/fuel mixture ratio.