Fuel tank, which has some expansion space at the top so fuel can expand on a hot day without overflowing or forcing the EVAP system to leak.The major components of the evaporative emission control system include: On newer vehicles, it is vented through the EVAP canister. On older EVAP systems, the tank is vented by a spring-loaded valve inside the gas cap. If the tank were sealed tight, the fuel pump would soon create enough negative suction pressure inside the tank to collapse the tank. For one thing, a fuel tank must have some type of venting so air can enter to replace fuel as the fuel is sucked up the fuel pump and sent to the engine. Sealing the fuel tank is not as simple as it sounds. HOW THE EVAPORATIVE EMISSION CONTROL SYSTEM WORKS EVAP has been used on all cars and light trucks since the early 1970s. The fuel vapors are hen burned in the engine.Įvaporative emission controls were first required on cars sold in California in 1970. When the engine is warm and the vehicle is going down the road, the PCM then opens a purge valve allowing the vapors to be siphoned from the storage canister into the intake manifold. Vent lines from the fuel tank and carburetor bowl route vapors to the EVAP storage canister, where they are trapped and stored until the engine is started. The EVAP system totally eliminates fuel vapors as a source of air pollution by sealing off the fuel system from the atmosphere. Uncontrolled evaporative emissions like this can account for as much as 20 percent of the pollution produced by a motor vehicle. That means if the fuel system is unsealed or open to the atmosphere, it can pollute 24 hours a day even if the vehicle is not being driven. The bad thing about fuel vapors is that fuel evaporates any time there is fuel in the tank. Often called instant smog because they can form smog without undergoing photochemical changes. These substances react with air and sunlight (called a photochemical reaction) to form smog. These include aldehydes, aromatics, olefins, and higher paraffins. The lighter elements in gasoline evaporate easily, especially in warm weather. The EPA requires EVAP systems on cars because gasoline fuel vapors contain a variety of different hydrocarbons (HC). And if you have a P0442 small leak code, you will probably have to take your car to a repair shop that has a smoke machine. The smoke may also contain an ultraviolet dye to make it easier to see under UV light.įixing EVAP codes can be a challenge, even for professional technicians. The smoke machine feeds a mineral-oil based vapor into the EVAP system under light pressure (no more than a few pounds per square inch). By small, we mean a leak no larger than a pin prick! Such small leaks are virtually impossible to find visually, so a special tester called a smoke machine is usually necessary to reveal the leak. This indicates the system has detected a SMALL leak, but small leaks can often be a BIG problem to find. The code you don't want to see is a P0442. EVAP Purge valve codes (P0443 to P0449) are also common). The most common fault code is P0440, which indicates a large leak (often a loose gas cap). This may create a problem for the vehicle owner if his vehicle must be given an OBD II plug-in emissions test and the monitor has not completed.Ĭommon problems with the EVAP system include faults with the purge valve that vents fuel vapors to the engine, leaks in vent and vacuum hoses, and loose, ill-fitting or missing gas caps. However, the EVAP monitor only runs under certain operating conditions. The OBD II EVAP monitor on 1996 and newer vehicles runs diagnostic self-checks to detect fuel vapor leaks, and if it finds any (including a loose or missing gas cap), it will set a fault code and turn on the Check Engine light. The EVAP system usually requires no maintenance, but faults can turn on the Check Engine light and prevent a vehicle from passing an OBD II plug-in emissions test. The Evaporative Emission Control System (EVAP) is used to prevent gasoline vapors from escaping into the atmosphere from the fuel tank and fuel system. Auto Repair Library, Auto Parts, Accessories, Tools, Manuals & Books, Car BLOG, Links, IndexĮVAP Evaporative Emission Control System by Larry Carley copyright 2019
0 Comments
Leave a Reply. |