A system and method of detecting fueling imbalance(s) in an internal combustion engine is provided. The method includes receiving data regarding an oxygen content of engine exhaust for the engine operating at a cycle rate. Frequency component analysis is performed comprising a filtering operation on the received oxygen content data. The filtering is done at the cycle rate of the engine or harmonics thereof to obtain filtered oxygen content data. Then, the method/system determines at least one of: 1) one or more angles of the engine at which the filtered oxygen content data exhibits a first amplitude value characteristic relative to amplitude values at other angles; and 2) a shape of the filtered oxygen content data obtained by sampling at pre-defined engine angles. The method/system then identifies a cylinder experiencing a fueling imbalance responsive to the determined at least one of one or more angle(s) and shape of the data.