Patent ID: 7143755

Claim:
A system for controlling an air/fuel ratio of an internal combustion engine mounted on an outboard motor, comprising: detectors detecting operational state of the engine including an engine speed and engine load; an oxygen sensor disposed at an exhaust system of the engine and producing an output whose property changes near a stoichiometric air/fuel ratio; a first controller controlling the air/fuel ratio of the engine to the stoichiometric air/fuel ratio by correcting a basic fuel injection quantity to be supplied to the engine determined based on the detected operational state of the engine, by a feedback correction coefficient determined based on the output of the oxygen sensor; a memory having a plurality of storage areas divided by the engine speed and engine load and each storing a learned correction coefficient that is used for correcting the basic fuel injection quantity; a learned correction coefficient calculator calculating the learned correction coefficient based on the feedback correction coefficient; a learned correction coefficient updater updating the learned correction coefficient by writing the calculated learned correction coefficient over the stored learned correction coefficient, when the engine load is within a predetermined range relative to the engine speed; and a second controller retrieving the learned correction coefficient from the engine speed and engine load and controlling the air/fuel ratio to one other than the stoichiometric air/fuel ratio by correcting the basic fuel injection quantity by at least the retrieved learned correction coefficient.