Positive pressure canister purge system integrity confirmation

摘要

The tank/canister volume's integrity against unacceptable leakage is either confirmed or denied by a diagnostic test performed by an on-board diagnostic system which includes an electrically operated air pump and tank-mounted analog pressure transducer. At the beginning of a test, the engine management computer closes the canister purge solenoid valve and operates the pump to begin pressurization of the tank/canister volume. The pumped air is introduced via the canister's atmospheric vent port so that the pressurizing air is entrained with fuel vapors previously collected in, but not yet purged from, the canister. Failure to build to a predetermined pressure within a predetermined time indicates a gross leak. Upon attainment of the predetermined pressure, the pump is shut off. If the pressure drops by more than a certain amount during the test, integrity is denied. If not, integrity is confirmed.