Pulse interval leak detection system

In an engine-powered automotive vehicle evaporative emission control system comprising an evaporative emission space for containing volatile fuel vapors, and a leak detection system for detecting leakage from the evaporative emission space, the improvement in said leak detection system which comprises:

• initial pressurizing means operable at the beginning of a test for creating in the evaporative emission space, an initial test pressure that differs sufficiently from atmospheric pressure to allow a leak to be detected;
• pressure restoring means operable after attainment of the initial test pressure in the evaporative emission space for restoring the initial test pressure in the evaporative emission space whenever the pressure changes from the initial test pressure by a predetermined amount, thereby indicating a leak;
• and
• measuring means for measuring leakage after the indication thereof, the measuring means comprising:
• 1) time interval measuring means for measuring at least one of a) a time interval required for pressure in the evaporative emission space to change from the initial test pressure by the predetermined amount, and b) a time interval required for the pressure restoring means to restore the initial test pressure in the evaporative emission space, whereby at least one time interval measurement is obtained;
• and 2) processing means for processing the obtained at least one time interval measurement to obtain a measurement of leakage.