Closed Loop Feedback Control System

The heart of the emissions control system is the closed loop fuel feedback control system. It is responsible for controlling the content of the catalytic converter feed gas and ultimately determines how much hC, CO and NOx leaves the tailpipe. The closed loop control system works primarily during idle and cruise operations and makes adjustments to injection duration based on signals from the exhaust oxygen sensor.

During closed loop operation, the ECM keeps the air/fuel mixture modulated around the ideal 14.7 to 1 air/fuel ratio (stoichiometry). By precisely controlling fuel delivery, the oxygen content of the exhaust stream is held within a narrow range that supports efficient operation of the three-way catalytic converter. However, if the air/fuel ratio begins to deviate from its preprogrammed swings, catalyst efficiency falls dramatically, especially the reduction of NOx.

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