Fuel Vapor Recovery System (Duty Cycle Purge Control)

Duty Cycle Purge is a system that feeds fuel gases from purge canister and gasoline tank into throttle body for mixing with incoming air. Metering of gases is performed by duty cycling purge solenoid by PCM.

The system is disabled during wide open throttle conditions and while engine is below a specified coolant temperature. When engine temperature becomes greater than a calibrated parameter, duty cycle purge is delayed for a calibrated time. Once purge delay is over, purge will be ramped in to soften effect of dumping additional fuel into engine.

The PCM provides a modulated 5 Hz signal (at closed throttle) or 10 Hz signal (at open throttle) to control this system. Modulation of signal is based upon a calculated air flow (based upon known fuel flow through injector at a given pulse width and RPM) and is adjusted to compensate for changes in flow due to varying engine vacuum.