Abstract: Air/fuel imbalance monitoring systems and methods for monitoring air/fuel ratio imbalance of an internal combustion engine are disclosed. In one embodiment, an oxygen sensor is sampled above cylinder firing frequency and a ratio of data from at least one window over a total number of windows is determined. The approach can be used to indicate imbalances between engine cylinders.

Abstract: Air/fuel imbalance monitoring systems and methods for monitoring air/fuel ratio imbalance of an internal combustion engine having a plurality of engine cylinders are provided herein. An example of the method may include routing exhaust gas from a first group of cylinders to an exhaust gas oxygen sensor, and during selected operating conditions, indicating that air/fuel of at least one cylinder in the first group is imbalanced based on a response of the exhaust gas oxygen sensor at frequencies at or above firing frequency of the cylinders in the first group. An example of the system may include an exhaust gas oxygen sensor positioned in such a way that exhaust gas from the group of engine cylinders are routed to the exhaust gas oxygen sensor, and a controller configured to during selected operating conditions, indicate that air/fuel of at least one cylinder in the group is imbalanced based on a response of the exhaust gas oxygen sensor at frequencies at or above firing frequency of the cylinders in the group.