FAILURE DIAGNOSTIC EQUIPMENT FOR EVAPORATIVE FUEL SUPPLY SYSTEM

PROBLEM TO BE SOLVED: To provide failure diagnosing equipment used for an evaporative fuel supply system and capable of preventing misdiagnosis with respect to an evaporative route, and considering a decrease in sensitivity in oil level variation detecting means caused by a change in the surface area of the oil level (liquid level) due to variation in the residual quantity of fuel in a fuel tank. SOLUTION: The failure diagnostic equipment for an evaporative fuel supply system is provided with an evaporative fuel supply route 22 connecting a fuel tank 20 having different cross sections in the depth direction to an inlet passage 7 through evaporative fuel adsorbing means 24. Negative pressure is introduced into the evaporative fuel supply route 22. Failure diagnosis is applied to the evaporative fuel supply route 22 by referring to a change state in pressure in the evaporative fuel supply route 22. Oil level variation detecting means 21 is also provided to detect a variation in the oil level in the fuel tank 29. A diagnosis suspension means is also provided to suspend the failure diagnosis when the variation detected by means of the oil level variation detecting means 21 exceeds the prescribed threshold value. Threshold revising means is also provided to revise the threshold value in accordance with a change in the surface area of the oil level caused by variation in the residual quantity of fuel in the fuel tank 20.