The filling characteristics of a Newtonian electrolyte through a microchannel with grafted polyelectrolyte layer on its inner walls have been investigated. A reduced order model has been deployed for the analysis. The streaming potential triggered by the interfacial electrochemistry, followed by an involved electrostatic interaction between polyelectrolyte macromolecules and the electrolytic ions, alters the filling characteristics in the microchannel. An oscillatory behavior of the filling dynamics is observed as the interface moves in the capillary. It has been demonstrated that the capillary filling dynamics can be altered through selective and tunable input parameters used in the investigation. A qualitative study has been performed on the variation in the filling dynamics by invoking scaling-estimates of the reduced order model. The scales of various participating forces on a spatiotemporal map have been identified to demarcate various regimes of the filling dynamics.