Diagnostics of mechanisms and systems allows estimating their current state and taking measures if necessary to carry out preventive or other actions for elimination of possible malfunctions. Diagnostics of mechanical parts of combustion engines, as well as other mechanical devices, mechanisms and systems as a whole, is the relevant objective. The purpose of the paper is to research the possible use of time-frequency autocorrelated function to analyze the combustion engine vibration signals to determine possible defects in its work. The paper introduces the basic possible definition of engine operation processes characteristics, being accompanied by emergence of additional frequency components in a spectrum of engine vibrosignal. The time-frequency correlation analysis allows receiving out of spectrum of engine vibrosignal additional information on weak periodic signals characterizing existence of any malfunctions of its mechanical part.