Diagnostic system for detecting leakage of fuel vapor from purge system

摘要

A leakage diagnostic system for making a judgement of leakage of a fuel purge system, which has in order from the side of a fuel tank a control valve, a canister and a purge valve disposed in a purge passage and a relief valve isolating the canister from the atmosphere, based on a rising rate of pressure in the purge passage between the fuel tank and the intake system isolated from the atmosphere after lowering and keeping the interior of the purge passage below specified negative pressure level for a specified period of time. When the interior of the fuel tank increases above a threshold level after a specified period of time, the leakage diagnostic system delivers a judgement of leakage of the purge system.