Fuel vapor leak test system and method comprising P-I-D setting of pulse bursts to regulate target pressure

This invention relates generally to a system and method for detecting gas leakage from an enclosed space, such as fuel vapor leakage from an evaporative emission space of a motor vehicle fuel system, especially to a system and method where a pump, such as a diaphragm pump, creates superatmospheric pressure in the space during a test. A leak test system and method for a motor vehicle fuel system. A pump forces air under pressure into vapor containment space. The pump operates in accordance with steps established by a processor. The pump creates superatmospheric target pressure in the space during an initial charging phase step, and after completion of that step, the pump is duty-cycled to regulate pressure in the space at the target pressure. A duty cycle comprises a burst of individual air pulses, one after another. The processor processes data corresponding to the duty cycle using P-I-D operations to set the number of pulses in a succeeding burst for regulating the pressure. When stability of the duty cycle is attained, the period of the duty cycle indicates leakage from the space.