A starved lubrication experiment and analytical model have been developed to investigate the friction condition transition (FCT) at the interface between a piston ring and a cylinder liner with the piston ring reciprocating liner test rig. To obtain a solution for the friction condition transition, phase space trajectories are used to extract the transient features of the friction force. The trajectories have three typical patterns for starved lubrication conditions. The irregular friction force of different strokes is classified based on the trajectories. When the projection of the trajectories in the phase space enters into the third pattern variation, this indicates the onset and progression of scuffing. The autocorrelation analysis of the wear surface topography at the stroke end validates the characterization method.