A method is disclosed for controlling an injector of a combustion engine. The injector includes an injection valve housing with an injection valve cavity, a valve needle axially movable within the injection valve cavity, a valve seat on which the valve needle rests in a closed position and from which the valve needle is lifted for an open position, and a spring element configured and arranged to exert a preload force on the valve needle acting to urge the valve needle in the closed position. A calibration value is provided, which is representative for the preload force. A base quantity is provided correlated to the fluid volume to be dispensed by the injector. A set-point opening time length is determined based on the calibration value and the base quantity. The valve needle of the injector is controlled to be in the opening position correlated to the set-point opening time length.