Abstract: A process for determining the fuel consumption or operating status of combustion engines having a fuel injection pump, a supply line connecting a fuel supply container to the fuel injection pump, and a return line connecting the fuel injection pump to the fuel supply container. Measuring devices are provided in each of the supply and return lines for recording flowing fuel volumes in the supply and return lines. The measuring devices each having a signal emitter or sensor sensing signals that are allocated respectively to the measuring devices. The measuring device in the return line includes at least two signal emitters or sensors. Signals are emitted from the measuring device in the return line that are a function of respective forward and reverse flow directions, which signals are supplied to a signal selector.