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This study is an experimental investigation of rare misfire and partial burn cycles in a spray-guided spark-ignited direct-injection optical engine. Spark discharge energy, discharge duration, flame imaging, velocity and equivalence ratio were measured every crank angle degree. Imaging was performed using high-speed 2-D particle image velocimetry (PIV) and planar laser inducted fluorescence (PLIF). The engine was operated near its optimum but produced rare and random partial burn and misfire cycles. Spark energy and spark duration for the partial burn and misfire cycles fell within the range of those for the well-burned cycles, with a slight bias toward low-energy, short-duration discharges, indicating no abnormal spark discharge events. PIV and PLIF measurements extracted from a 4mm×4mm region adjacent to and downstream of the spark plug at spark timing revealed that the partial burn and misfire cycles …