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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.

Misfire monitoring is currently a mandatory On Board Diagnostic (OBD) regulatory requirement in most of the main automotive markets. The most common method used for misfire detection is the one based on the calculation of the derivative of the angular crankshaft velocity in which sharp variations of the derivative signal are associated to misfire events. Therefore, the misfire detection calibration is practically unique for a given engine hardware and installation. Within this context, this Paper will present a practical evaluation and also a computational simulation of the impact of an engine hardware change (front end accessory drive dumpers) on the calculated angular acceleration signal and, therefore, on the overall misfire detection capability. The outcomes of this study will ultimately define the need of calibration changes as well as support a future development of an analytical method to predicted impacts in misfire calibration.