Abstract: An evaporation fuel processing mechanism supplies fuel vapor in a fuel tank to a canister via a vapor passage and purges fuel in the canister to an air-intake passage of an internal combustion engine via a purge passage when the internal combustion engine is operated. This mechanism supplies fuel vapor in the fuel tank when refueling to the canister via a breather passage. The breather passage has a pressure sensitive valve that opens in response to a variation in pressure in the fuel tank during refueling. An air-fuel ratio variation limiting apparatus determines whether the pressure sensitive valve is open and limits a variation in the air-fuel ratio when the pressure sensitive valve is open.

Abstract: A fuel injection control device in which the amount of fuel injected by the fuel injector is increased at the time of acceleration. Namely, at the time of acceleration, the lean time and the rich time of the air-fuel mixture are calculated during the lean-rich discriminating time, which is basically equal to a time of an occurence of the lean time and the rich time when the air-fuel ratio is maintained at the stoichiometric air-fuel ratio at the time of acceleration. When the lean time becomes considerably longer than the rich time, the amount of fuel injected by the fuel injector is further increased.