Patent ID: 8548718

Claim:
An air/fuel ratio variation abnormality detection apparatus for an internal combustion engine in which each of a plurality of cylinders has a plurality of fuel injection valves, comprising: an abnormality detection device that detects an inter-cylinder variation abnormality in an air/fuel ratio based on a fluctuation of a predetermined output of the internal combustion engine; an abnormal-place discernment device that, if the variation abnormality is detected, discerns which of the fuel injection valves and an intake path to the cylinders bears a cause of the variation abnormality based on the fluctuation of the predetermined output between before and after injection proportion between the plurality of fuel injection valves is altered; and an index value calculation device that, if it is discerned that the cause of the variation abnormality exists in one of the fuel injection valves, calculates an index value that represents a degree of the abnormality by normalizing the predetermined output regarding the fuel injection valve based on the injection proportion.