Method for operating a combustion engine

The method involves determining a variable, which characterizes a slope of a straight line (62) or a straight-shaped curve sections. The straight line or the straight-shaped curved actuation periods (52) of an injector are associated with each corresponding difference values (50). The difference value is formed by the difference between an actual closing time point (56) and a reference closing time point (58) or between an actual injection quantity (64) and a reference injection quantity (66). A measure for carbonization of the injector is determined from the determined variable. Independent claims are included for the following: (1) a computer program; and (2) a control and regulating device for an internal combustion engine.