Failure detection apparatus for fuel systems of engine

1. A failure detection apparatus for fuel systems of an engine capable of switching between a first injection form and a second injection form, the failure detection apparatus comprising:

a first failure determiner executing, while the engine is in operation in each of the first and second injection forms, a failure determination process on the corresponding fuel system;

a second failure determiner executing, when the first failure determiner determines occurrence of a failure during operation in one of the injection forms, a failure determination process on the fuel system corresponding to the other injection form during operation in the other injection form;

a failure locator assertively determining whether or not the failure has occurred, for each of the fuel systems responsible for the first and second injection forms, based on a result of the failure determination process by the second failure determiner; and

a purge process prohibiter prohibiting execution of a purge process of causing fuel evaporative emissions generated in a fuel tank to be adsorbed to a canister and introducing the fuel evaporative emissions into a cylinder while the engine is in operation, wherein

when the second failure determiner executes the failure determination process on the fuel system, the second failure determiner causes the purge process prohibiter to prohibit execution of the purge process.

2. The failure detection apparatus for the fuel systems of the engine according to claim 1 , wherein

the first failure determiner determines occurrence of a failure in the fuel system based on a fluctuation in air-fuel ratio toward a rich side or a lean side of the engine, and

when the first failure determiner determines occurrence of a failure, the second failure determiner executes, during operation in the other injection form, the failure determination process on the corresponding fuel system on condition that a predetermined intake air amount is satisfied in a current operation region of the engine.

3. The failure detection apparatus for the fuel systems of the engine according to claim 2 , wherein

the engine further comprises an intake air pressure detector detecting a pressure in an intake passage located downstream of a throttle valve, and

when the first failure determiner determines occurrence of a failure based on the fluctuation in air-fuel ratio toward the lean side, the second failure determiner executes, during operation in the other injection form, the failure determination process on the corresponding fuel system on condition that the intake air pressure detector detects a value smaller than or equal to a predetermined pressure.

4. The failure detection apparatus for the fuel systems of the engine according to claim 3 , wherein

the second failure determiner continues, until the engine is stopped, determination of whether or not the intake negative pressure is established or whether or not a supercharging pressure is established.

5. The failure detection apparatus for the fuel systems of the engine according to claim 2 , wherein

the engine further comprises

a supercharger supercharging intake air in a predetermined operation region, and

a supercharging state determiner detecting whether or not the supercharger is supercharging the intake air, and

when the first failure determiner determines occurrence of a failure based on a fluctuation in air-fuel ratio toward the rich side, the second failure determiner executes, during operation in the other injection form, the failure determination process on the corresponding fuel system on condition that the supercharging state determiner determines that supercharging is performed in the predetermined operation region.

6. The failure detection apparatus for the fuel systems of the engine according to claim 2 , wherein

when the second failure determiner executes the failure determination process on the fuel system, if the engine experiences a predetermined operation state before execution of the purge process is prohibited, the second failure determiner determines whether or not the intake air pressure detector has detected a value smaller than or equal to a corresponding predetermined pressure, and in a case where the intake air pressure is not generated, prohibition of execution of the purge process is cancelled.

7. The failure detection apparatus for the fuel systems of the engine according to claim 1 , further comprising

an intake air amount detector detecting an intake air amount of the engine, wherein

when the first failure determiner determines occurrence of a failure, the second failure determiner executes, during operation in the other injection form, the failure determination process on the corresponding fuel system on condition that a first filling efficiency determined from an intake air amount detected by the intake air amount detector is substantially equal to a second filling efficiency determined from an intake air pressure and a rotation speed of the engine.

8. The failure detection apparatus for the fuel systems of the engine according to claim 1 , wherein

the second failure determiner causes the purge process prohibiter to prohibit execution of the purge process when starting the failure determination process on the fuel system, and causes the purge process prohibiter to cancel the execution prohibition immediately when a result of the failure determination process is obtained.