In a first operating state, the fuel metering of one of the cylinders is controlled in first metering pulses with the same pulse characteristic during a respective one working cycle, and the metering of fuel into the other cylinders by at least one second metering pulse with a different pulse characteristic. The first pulse number and characteristic is predefined such that the same fuel mass should be metered based on an assumed injection valve characteristic as with the one second metering pulse. Depending on the measurement signal, a correction value for the one cylinder is determined. To meter the fuel based on the assumed injection valve characteristic, a single first metering pulse would be generated during a respective one working cycle. The correction value for the one cylinder is used during the rest of the operation to adapt the first metering pulse in the second operating state.