The fuel vapor recovery system was the most neglected part of a vehicle’s emission system, according to the Environmental Protection Agency (EPA).
Automotive fuel systems are not truly sealed. They are vented to maintain pressure as fuel is added or used. Refueling, temperature fluctuations, and evaporation create excess fuel vapor. The Evaporative Emissions System must handle this hydrocarbon (HC) vapor.
Factory emission tests have determined that an EVAP system with a leak as small as .020” can yield an average of 1.35 grams of HC per vehicle driven mile. This is 30 times over the current allowable exhaust emissions standard.
In addition to causing HC emissions, the EVAP system's failure wastes fuel and often creates customer concern about gasoline odors.
This video, without audio, was developed by California Air Resources Board (CARB). It shows actual hydrocarbon vapors created by removing a gas cap, removing the nozzle from the filler next, and filling a container with fuel. These actions are performed daily by millions of people.