Diagnosis apparatus for fuel vapor purge system

摘要

An improved diagnosis apparatus for detecting leakage of a fuel vapor purge system that purges fuel vapor from a fuel tank to an intake passage of an engine. The apparatus includes a pressure sensor and a purge valve. The pressure sensor detects the pressure in the purge system. The purge valve connects the purge system with the intake passage for lowering the purge system pressure to a predetermined pressure level. After the purge system pressure is lowered to the predetermined level, the purge system is sealed. The apparatus measures the rate of pressure change immediately after the purge system is sealed. The apparatus subsequently measures the rate of pressure change when the purge system pressure reaches a second reference pressure value and computes the ratio of the rates. The apparatus diagnoses whether there is a leak in the purge system based on the ratio and the rate of pressure change at the second reference pressure value.