Mixture Ratio Feedback Control System

Mixture Ratio Feedback Control:

PURPOSE AND OPERATION
Mixture ratio feedback system is designed to precisely control the mixture ratio to the stoichiometric point so that the three-way three way catalyst can reduce CO, HO and NOx emissions.
This system uses an heated oxygen sensor in the exhaust manifold to check the air-fuel ratio. The ECCS control module (ECM) adjusts the injection pulse width according to the sensor voltage so the mixture ratio will be within the range of the stoichiometric air-fuel ratio. This stage refers to the closed-loop control condition. The open-loop control condition refers to that under which the ECM detects any of the following conditions and feedback control stops in order to maintain stabilized fuel combustion.
1) Deceleration
2) High-load operation
3) Engine idling
4) Malfunction of heated oxygen sensor or its circuit
5) Insufficient activation of heated oxygen sensor at low engine coolant temperature
6) Engine starting
7) Hot-engine operation
8) When all of the following conditions are met:
^ ignition switch "ON"
^ Soft closed throttle position switch "ON"
^ Neutral position switch "OFF"
^ Engine running at idle speed
^ Vehicle running at slow speed

MIXTURE RATIO SELF-LEARNING CONTROL
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from the heated oxygen sensor. This feedback signal is then sent to the ECM to control the amount of fuel injection to provide a basic mixture ratio as close to the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as originally designed. This is due to manufacturing errors (e.g., mass air flow sensor hot wire) and changes during operation (injector clogging, etc.) of Electronic Concentrated Engine Control System (ECCS) parts which directly affect the mixture ratio. Accordingly, a difference between the basic and theoretical mixture ratios is quantitatively monitored in this system. it is then computed in terms of "fuel injection duration" to automatically compensate for the difference between the two ratios.