Method for operating fuel system, controller and fuel system

The invention relates to a method for operating a fuel system of an internal combustion engine, the system comprises a gas rail for a gaseous first fuel, a liquid fuel rail for a liquid second fuel, and a dual fuel injector attached to the gas rail and the liquid fuel rail for injecting or injecting fuel into a combustion chamber of the internal combustion engine, the pressure in the gas rail is regulated by means of a hydraulically controlled gas pressure regulator, and the liquid fuel in the liquid fuel rail is supplied to the gas pressure regulator via an input throttle device for hydrauliccontrol. According to the invention, in the learning operation mode, the pressure in the gas rail is forced to be equal to the pressure in the liquid fuel rail, an electrically actuatable overflow valve is closed until the gas pressure regulator sets the pressure in the gas rail to the pressure in the liquid fuel rail in the form of a pressure balance, and the overflow valve is used to return theamount of liquid fuel sup