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• A closed loop feedback controlled fuel management system is used for precise control of air-fuel ratio. A simple closed-loop feed back engine fuel management system is shown schematically in Fig. 5.15.
• An oxygen sensor installed in the exhaust system detects presence of free oxygen in the exhaust gas which determines whether the fuel-air mixture is leaner or richer than stoichiometric.
• The signal from the oxygen sensor is fed to a microprocessor controlled fuel management system to adjust fuel injection rate so that the engine operates in a narrow window around the stoichiometric set point.
• Fuel-air ratio oscillates around the set point at a frequency of 0.5 to 1 Hz as the fuel flow is varied.

     Signals of air mass flow rate, engine load, speed, spark timing temperatures and several other parameters are also fed to the engine electronic control unit for management of engine operation. Carburetors were found to be incompatible with such control systems although initially electronically controlled carburetors were developed and used. Now, multipoint port fuel injection system is a standard feature of engines using 3-way catalytic converters.