Method and apparatus for monitoring a multiple step valve lifter

A method and system for monitoring performance of an internal combustion engine equipped with individually actuated valve control mechanisms, such as a two-step finger-follower rocker-arm assembly, using a strategy that identifies cylinder-to-cylinder variations, is disclosed. The method and system preferably include monitoring engine operating conditions, based upon input from an exhaust gas sensor and engine sensors, and determining an engine operating point. Individual cylinder fueling modifiers are determined, each corresponding to one of the cylinders at the determined engine operating point, based upon input from the exhaust gas sensor. It is determined that the each individually actuated valve control mechanism is operating properly when a difference between the individual cylinder fueling modifier and a predetermined individual cylinder fueling modifier, each said modifier determined for the corresponding cylinder at the determined engine operating point, is less than a predetermined difference.