Cpv-controlled evap leak detection system

In an evaporative emission control system, controlled by a Powertrain Control Module and having a fuel tank in fluid communication with a carbon canister, the carbon canister being in fluid communication with an engine intake manifold, the improvement wherein the control system includes a leak detection system, comprising:

• a vacuum pump having a first port in fluid communication with an ambient atmosphere, and a second port in fluid communication with the evaporative emission control system;
• a canister purge valve (CPV) positioned in a fluid communication line between the canister and the intake manifold, configured operably connected to the PCM;
• wherein the PCM is configured to control the CPV to open the CPV by an amount sufficient to provide a flow equivalent to a predetermined orifice diameter.
• a pressure sensor configured to sense pressure of a small volume within the system, the small volume being defined by the vacuum pump, the CPV, a fuel tank isolation valve, and fluid communication lines associated with those devices;
• and
• at least one changeover valve configured to alter fluid flow paths and directions, wherein the vacuum pump, the pressure sensor, and the at least one changeover valve constitute an Evacuation Level Check Monitor (ELCM).