Method for the combined identification of a piston stroke phase difference, of an inlet valve stroke phase difference and an outlet valve stroke phase difference of a cylinder of a series-production internal combustion engine during operation, wherein - dynamic pressure oscillations, assignable to the cylinder, of the intake air in the air intake tract and/or of the exhaust gas in the exhaust-gas outlet tract of the respective series-production internal combustion engine are measured during operation and a corresponding pressure oscillation signal is generated from these, and wherein a crankshaft phase angle signal is determined at the same time, - wherein, from the pressure oscillation signal, using discrete Fourier transformation, the phase positions of more than two selected signal frequencies of the measured pressure oscillations in relation to the crankshaft phase angle signal are determined, characterized by the following further steps: - on the basis of the determined phase positions of the respective selected signal frequencies, determining more than two lines of equal phase positions of the selected signal frequencies, which lines are dependent on inlet valve stroke phase difference and outlet valve stroke phase difference, using reference lines of equal phase positions, which reference lines are stored in reference line characteristic maps or determined by means of a respective algebraic model function; - determining a single common intersection point of the determined lines of equal phase positions of the selected signal frequencies by projection into a common plane spanned by inlet valve stroke phase difference and outlet valve stroke phase difference and signal-frequency-dependent phase shifting of the determined lines of equal phase positions; - determining the inlet valve stroke phase difference and the outlet valve stroke phase difference from the determined single common intersection point of the lines of equal phase positions of the selected signal frequencies, and - determining the piston stroke phase difference from the values of the phase shift that has been performed to the single common intersection point of the lines of equal phase positions of the selected signal frequencies. - dynamic pressure oscillations, assignable to the cylinder, of the intake air in the air intake tract and/or of the exhaust gas in the exhaust-gas outlet tract of the respective series-production internal combustion engine are measured during operation and a corresponding pressure oscillation signal is generated from these, and wherein a crankshaft phase angle signal is determined at the same time, - wherein, from the pressure oscillation signal, using discrete Fourier transformation, the phase positions of more than two selected signal frequencies of the measured pressure oscillations in relation to the crankshaft phase angle signal are determined, characterized by the following further steps: - on the basis of the determined phase positions of the respective selected signal frequencies, determining more than two lines of equal phase positions of the selected signal frequencies, which lines are dependent on inlet valve stroke phase difference and outlet valve stroke phase difference, using reference lines of equal phase positions, which reference lines are stored in reference line characteristic maps or determined by means of a respective algebraic model function; - determining a single common intersection point of the determined lines of equal phase positions of the selected signal frequencies by projection into a common plane spanned by inlet valve stroke phase difference and outlet valve stroke phase difference and signal-frequency-dependent phase shifting of the determined lines of equal phase positions; - determining the inlet valve stroke phase difference and the outlet valve stroke phase difference from the determined single common intersection point of the lines of equal phase positions of the selected signal frequencies, and - determining the piston stroke phase difference from the values of the phase shift that has been performed to the single common intersection point of the lines of equal phase positions of the selected signal frequencies. - on the basis of the determined phase positions of the respective selected signal frequencies, determining more than two lines of equal phase positions of the selected signal frequencies, which lines are dependent on inlet valve stroke phase difference and outlet valve stroke phase difference, using reference lines of equal phase positions, which reference lines are stored in reference line characteristic maps or determined by means of a respective algebraic model function; - determining a single common intersection point of the determined lines of equal phase positions of the selected signal frequencies by projection into a common plane spanned by inlet valve stroke phase difference and outlet valve stroke phase difference and signal-frequency-dependent phase shifting of the determined lines of equal phase positions; - determining the inlet valve stroke phase difference and the outlet valve stroke phase difference from the determined single common intersection point of the lines of equal phase positions of the selected signal frequencies, and - determining the piston stroke phase difference from the values of the phase shift that has been performed to the single common intersection point of the lines of equal phase positions of the selected signal frequencies.