Nowadays the automotive industry and the motor development are one of the most dynamically developing industries. One solution to the diagnostic systems providing reliability is the acoustic and vibration measurement system, which can indicate and predict a variety of malfunctions after signal processing. The purpose of this experiment is to analyze the effect of the air-fuel equivalence ratio on the vibration components of an internal-combustion engine (ICE) which is a part of the in question measurement system. In the focus of the experiments are the analysis of the time signal, its spectra, and the power content of the signal. With the increment of the air-fuel ratio the amplitudes of the measured signal and its spectral amplitudes showed a downward trend as the RMS values. In addition, certain frequency components disappeared during the actuation of the ICE with an electromotor, so the characterization of the combustion could be come to the front.