Methods and systems are provided for controlling a duty cycle of a purge valve configured to regulate a purge flow from a fuel vapor storage canister to an intake of an engine during canister purging events. In one example, a method includes controlling a duty cycle of a purge valve configured to regulate a purge flow from a fuel vapor storage canister to an intake of an engine during a canister purging event based on a degradation factor obtained by comparison of durations at which a predetermined pressure is reached in an evaporative emissions system at multiple purge valve activation levels. In this way, a flow map stored at a controller may be updated for controlling the purge valve during subsequent purging events.