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A new vibration signal processing technique is applied to a four-cylinder spark ignition engine for characterization of its transient motion during crank-on/idling/engine-off. This technique utilizes the directional Wigner distributions(dWDs) of the transient complex-valued vibration signals measured from the engine block. In order to avoid the aliasing problem and the interference terms between the forward(positive) and backward(negative) frequency components, the transformations of complex-valued signals to the forward and backward pass analytic signals were developed for calculation of the two types of dWDs: the auto-dWD essentially tracks the shape and directivity of the instantaneous planar motion, whereas the phase of the cross-dWD indicates its inclination angle.