A method for adjusting a lookup table that includes preset on-time values for an injector of an engine linked to fuel injection quantity values (δ). The following steps are executed in a situation when the output shaft of the engine is disconnected from the output shaft of the gearbox. A torque loss value (Tloss) and a combustion efficiency value (εF) are determined or received. An actual fuel injection quantity value (δactual) is calculated, based on the torque loss value and the combustion efficiency value. An on-time value (tg) linked to the actual fuel injection quantity value is determined from the lookup table and the on-time value is compared with a presently applied on-time value (tb) that is established by an engine control with the aid of a regulator and the lookup table. The lookup table is adjusted based on the result of the comparison.