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The purpose of this study was to develop a method for detecting combustion fluctuation and noise to improve homogeneous charge compression ignition (HCCI) engine system robustness. In the present study, the maximum rate of pressure rise (dp/dθmax) was used as an index of noise and the standard deviation of indicated mean effective pressure (σIMEP) was used as an index of HCCI combustion fluctuation. A knock sensor and crank angle sensor, which are equipped with a conventional spark ignition (SI) engine system, were used as combustion noise and fluctuation detection sensors. For acquiring knock sensor signals, the time series of data were analyzed using fast Fourier transformation (FFT). The integral value of the power spectrum shows the vibration intensity of the engine. For acquiring crank angle sensor signals, the time series of data were analyzed using the average calculation of crankshaft revolution.