Fill Control/Vent System
WARNING: This page is about a different car, the 1995 Ford Bronco. However, it is still accessible from the selected car via links, so may be relevant.
Fill limiting is accomplished through configuration of fill neck and/or internal vent lines. Vent system is designed to permit air space in 10-12 percent of tank to allow for thermal expansion.
Vapor generated in fuel supply line is continuously vented back to fuel tank. Venting prevents engine surging from fuel enrichment and assists in hydrocarbon (HC) emission control.