Method and apparatus for determining a fuel wall film mass

Method for determining a fuel wall film mass in an internal combustion engine (1) with intake manifold injection, wherein the fuel wall film mass is determined in a first method section, starting from a fuel injection, the fully before opening of an intake valve (5) of a cylinder (20) of the internal combustion engine (1) in the suction tube (10), and that in a second process section corrects the thus determined value for the fuel wall film mass in dependence of the ratio between the via the open inlet valve (5) into a combustion chamber (15) of the cylinder (20), the injected fuel mass and the total injected fuel mass becomes.