US Patent 7438060 System for detecting purge valve malfunction

A diagnostic control system for a purge valve that regulates fuel vapor flow from a fuel system into an intake manifold for an engine includes a calculation module and a malfunction module. The calculation module estimates a plurality of areas based on a plurality of pressure signals and calculates an average rate of increase of vacuum pressure in the fuel system during operation of the purge valve. The malfunction module determines whether the average rate of increase of vacuum pressure is within a predetermined range generating a purge valve functioning signal, and generates a purge valve malfunction signal when the average rate of increase of vacuum pressure is not within the predetermined range.