The fuel vent valve sits atop the fuel tank and vents vapors into the charcoal canister, which are then burned off in the combustion chamber as part of the normal operation of the vehicle. Normally functioning valves remove air from the fuel system as it tries to settle into the tank. These components can wear over time, leading to misfires, reduced fuel efficiency and increased emissions.
The fuel tank vent valve is attached to the fuel tank using a series of seals and connectors. If these become damaged or wear greatly over time, they can cause fuel to flow into the charcoal canister and the combustion chamber when the engine is cold. This can lead to serious engine and emissions system issues. Replacing a damaged vent valve or vent valve seal can help ensure that vapors flow only when desired. Malfunctioning vents prevent fuel from flowing properly through the system, resulting in over-rich mixtures, which can damage catalytic converters or cause engine misfires due to incorrect quantities of fuel and air in the combustion chamber. Because replacing these parts requires working with the fuel tank and fuel system, it is recommended that it only be undertaken by experienced automotive mechanics.