An experimental investigation aiming at extending the operating range of lean-burn turbocharged spark-ignition (SI) CNG engine was conducted on a six-cylinder throttle body injection CNG engine. Cylinder pressure was recorded by using a high sampling frequency transducer, thus allowing the analysis of pressure characteristics introduced by knock. Coefficient of variations (COV) in indicated mean effective pressure (IMEP) was used to define lean misfire. The effects of various engine parameters on an engine's lean burn capability, knock limit, and preturbo temperature limit were examined at various operating conditions. The results indicate that a lean-burn SI CNG engine's operating range is sensitively affected by the mechanical structure of the engine, excess air ratio, spark timing, load, engine speed, intake temperature, ambient humidity, etc. For the turbocharged engine, preturbo temperature is also a key consideration in extending the operating range of the engine.