Abstract: An onboard diagnostic mechanism for a sealed vehicle fuel delivery system. By controlling fuel system valves, the electronic engine controller (EEC) periodically subjects the sealed system to an initial vacuum level, then monitors the pressure increase due to evaporative effects during a predetermined test interval. Excessive deviations in measured pressure compared to predetermined criteria produce indications of potential undesired operational conditions. To prevent fuel sloshing which results from aggressive driving or rough roads from producing false output indications, the instantaneous system pressure is compared with a rolling average of tank pressure to produce a difference signal indicative of fuel sloshing. If the resulting difference signal exceeds a predetermined threshold, the monitoring process is aborted in favor of a later test after the fuel sloshing condition terminates.

Abstract: A method and system for determining a level of vapor generated by an evaporative system. The evaporative system is closed to atmosphere. An initial pressure in a fluid-filled tank is sensed and, after a predetermined amount of time, a second pressure in the tank is sensed. A pressure difference is determined based on the sensed initial pressure and the sensed second pressure. The level of vapor generated by the evaporative system is determined based on the pressure difference.