Method for controlling an injector of a combustion engine, wherein - the injector comprises - an injection valve housing with an injection valve cavity, - a valve needle being axially movable with 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, - a spring element being designed and arranged to exert a preload force on the valve needle acting to urge the valve needle in the closed position, - a calibration tube being designed and arranged to form a seat for the spring element, wherein the preload force is during manufacturing of the injector adjustable for a predetermined injection volume at a predetermined fluid pressure for a predetermined opening time length by changing the axial position of the calibration tube, - a calibration value is provided, which is representative for the preload force, and wherein the calibration value is dependent on the axial position of the calibration tube, - a base quantity is provided, correlated to the fluid volume to be dispensed by the injector, - dependent on the calibration value and the base quantity a set-point opening time length is determined to operate the injector for the injector-specific set-point opening time length, which takes into account the injector-specific calibration value, - the valve needle of the injector is controlled to be in the open position correlated to the set-point opening time length. - the injector comprises - an injection valve housing with an injection valve cavity, - a valve needle being axially movable with 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, - a spring element being designed and arranged to exert a preload force on the valve needle acting to urge the valve needle in the closed position, - a calibration tube being designed and arranged to form a seat for the spring element, wherein the preload force is during manufacturing of the injector adjustable for a predetermined injection volume at a predetermined fluid pressure for a predetermined opening time length by changing the axial position of the calibration tube, - an injection valve housing with an injection valve cavity, - a valve needle being axially movable with 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, - a spring element being designed and arranged to exert a preload force on the valve needle acting to urge the valve needle in the closed position, - a calibration tube being designed and arranged to form a seat for the spring element, wherein the preload force is during manufacturing of the injector adjustable for a predetermined injection volume at a predetermined fluid pressure for a predetermined opening time length by changing the axial position of the calibration tube, - a calibration value is provided, which is representative for the preload force, and wherein the calibration value is dependent on the axial position of the calibration tube, - a base quantity is provided, correlated to the fluid volume to be dispensed by the injector, - dependent on the calibration value and the base quantity a set-point opening time length is determined to operate the injector for the injector-specific set-point opening time length, which takes into account the injector-specific calibration value, - the valve needle of the injector is controlled to be in the open position correlated to the set-point opening time length.