Purge Valve

The Powertrain Control Module (PCM) waits until the engine is running above 40°C (104°F) coolant temperature, with closed loop fueling system, before the purging process is activated. Under these conditions the engine should be running smoothly with no warm up enrichment. The purge valve duty (and flow) is initially ramped slowly because the vapor concentration is unknown and a sudden increase in purge could cause the engine to stall or loss of air fuel ratio control to occur. The concentration is then determined from the amount of adjustment that the closed loop fueling system is required to make to achieve the target air fuel ratio. Once the concentration has been determined, the purge flow can be increased and the injected fuel can be proactively adjusted to compensate for the known purge vapor and the target air fuel ratio control is maintained.