A method of operating an engine having an after-treatment system that treats exhaust gas from the engine with an oxidation catalyst includes adjusting the operation of the engine to increase the temperature of the exhaust gas, continuously sensing a cylinder pressure with a pressure sensor disposed at at least one cylinder of the engine to identify a unstable combustion event, i.e., an engine misfire, and adjusting the operation of the engine to prevent a future unstable combustion event when the unstable combustion event is detected.