According to CONAMA Resolution 354/2004, all passenger and light commercial vehicles manufactured in or imported to Brazil (except compression ignition engines) must be equipped, from 2010 on, with the Brazilian On Board Diagnostic level 2 (OBDBr-2). Among the OBDBr-2 features, the misfire detection is by far the most challenging due to the Brazilian Flex Fuel context and also due to its interface with several powertrain components. Ford Motor Company has developed a series of peculiar studies and validation procedures to check the robustness and effectiveness of the OBDBr-2 misfire monitor. One of them focused on the correlation between engine production variation and misfire monitor detection capability. Experiments were performed varying the following characteristics: crankshaft position sensor air gap, torque to turn, spark plug depth and compression variation among cylinders. The results of the analysis of the mentioned experiments helped Ford Motor Company to revise its misfire monitor calibration in order to make it more robust and compliant with the regulation within a wide range of product variation.