Patent ID: 6487892
Filing Date: 2002-12-03
Classification: F02M

Abstract:
A method for testing a purge system that purges fuel vapor in a fuel tank to an intake passage of an engine through a system passage connected with the fuel tank, wherein the purge system includes the fuel tank, the system passage, a first valve and a second valve, the method comprising:starting the testing when the pressure in the purge system is stable for a predetermined period; changing the pressure in the purge system to a first predetermined pressure that is lower than the atmospheric pressure; sealing the purge system; monitoring the change of the pressure in the sealed purge system and detecting leakage of fuel vapor from the purge system; evaluating a result of the monitoring; demanding that the testing of the purge system be restarted when the result is improper; restoring the pressure of the purge system substantially to the atmospheric pressure when a restart of the testing is demanded, wherein the first valve is located between the system passage and the intake passage to purge fuel vapor to the intake passage and the second valve disconnects the system passage from the atmosphere, wherein the step of changing the pressure in the purge system includes opening the first valve and closing the second valve so that the system passage is connected to the intake passage, wherein the step of changing the pressure includes monitoring the change of the pressure in the purge system and diagnosing the first valve substantially simultaneously with changing the pressure, wherein the step of sealing the purge system includes monitoring the change of the pressure in the purge system and diagnosing the first valve substantially simultaneously with sealing the purge system.