Method for operating a combustion machine, combustion machine and motor vehicle

A method is provided to determine the hydrocarbon content in the purge gas of a fuel tank system of a combustion machine, whereby the fuel tank system comprises at least a fuel tank, a fuel vapor filter that is fluidically connected to an atmospheric port, a vent line leading from the fuel tank to the fuel vapor filter, a purge gas line leading from the fuel vapor filter to the fresh gas line of the combustion machine, a fuel tank vent valve that is integrated into the purge gas line, a pressure sensor that is integrated into the purge gas line and that can be configured as an absolute pressure sensor or as a differential pressure sensor, and a compressor that is integrated into the purge gas line. In this context, it is provided that, during operation of the compressor, at least three pressure measurements are carried out in the purge gas line over a defined period of time by means of the pressure sensor and, only at the end of this period of time, on the basis of the determined pressure values, the loading of the purge gas with hydrocarbons is qualitatively determined in the purge gas that had flowed through the purge gas line during the period of time. Aside from the determination of the quantitative loading, which is preferably carried out parallel to the determination of the qualitative loading, the determination according to the invention of the qualitative loading allows a very precise assessment of the influence that the purge gas-which is fed to the fresh gas line of the combustion machine and from there to the internal combustion engine-exerts on the combustion processes during operation of the internal combustion engine.