Zero secondary flow ejectors/vacuum ejectors are primarily used to produce low back pressure condition in a high altitude test facility where high area ratio nozzles are tested at ground level condition. Here we performed experiments in the subscale model of the vacuum ejector to study the flow physics involved during the starting as well as stopping transient operation. Simultaneous acquisition of unsteady pressures and time resolved schlieren helped in establishing a relation between the jet dynamics to the unsteady pressure fluctuation in the secondary chamber of the vacuum ejector. The degradation of vacuum for pressures higher than the starting jet chamber pressure was studied. The pressure evolution curve of the vacuum ejector operation during the started regime showed the degradation of vacuum level for pressure ratio values above and below the optimum line of operation. The modal analysis of the time resolved schlieren images revealed the influence of longitudinal and lateral oscillations of the jet on the unsteadiness measured in the secondary chamber. The frequency of the longitudinal oscillation and lateral oscillation of the jet were found for different cases of unstarted (P0 = 2, 3 bar) and started condition (P0 = 3.8 bar). It was found that the frequency of oscillation of lateral modes were higher compared to the longitudinal mode of oscillation. The jet oscillation mode responsible for causing frequency peak at started mode of operation (P0 = 3.8 bar) was also identified.