Enhanced vacuum decay diagnostic and integration with purge function

Abstract

The present invention relates a method of detecting leaks and blockages in a fuel system. The leaks are detected using a RAMPOFF mode and a TANK mode. The RAMPOFF mode modifies the evaporative diagnostic purge logic to increase the ramp down rates of the evaporative purge duty cycle to aggressively shut off the purge solenoid valve for tests used to detect leaks as small as 0.02 inches in diameter. The TANK mode modifies the evaporative diagnostic purge logic to support aggressive purging requirements for tests used to detect larger leaks of greater than 0.04 inches in diameter. The MASS FLOW mode modifies the evaporative diagnostic purge logic to hold a constant purge mass flow rate necessary to detect blockages across a vent solenoid valve. The RAMPOFF mode, TANK mode, and MASS FLOW modes support evaporative diagnostics that are run continuously within a fuel system when acceptable engine operating conditions are present.

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