Servo controlled evap leak detection system

An evaporative leak check system, comprising:

• at least one passage facilitating a fluid communication between an outside atmosphere and a system interior;
• a vacuum pump in fluid communication with at least one passage and configured to carry out evacuating operations based on a first position and a second position, wherein in the first position the vacuum pump facilitates determination of a reference pressure value or a pressure threshold value, and in the second position the vacuum pump facilitates determination of a system pressure value;
• a changeover valve to switch between the first position and the second position;
• and
• a servo controlled variable reference orifice facilitating determination of the pressure threshold value.

A method for diagnosing leaks in an evaporative emission control system, comprising

• setting a variable reference orifice to a preselected diameter, that setting being enabled by a servo control.
• evacuating a reference volume in the vicinity of the variable reference orifice, using a vacuum pump, the reference volume being defined by the vacuum pump, the reference orifice, and associated fluid communication lines;
• determining a pressure in the reference volume at the end of a specified evacuation time;
• storing the determined pressure as the threshold test value;
• evacuating the system for a predetermined time;
• and
• identifying the presence of a leak if, after the evacuation, the system pressure falls at least to the threshold test value.