The evaporation system, also called EVAP on an automotive vehicle, traps and captures hydrocarbon vapors in the fuel system, which is related to emission control. The EVAP system recovers gas tank vented vapors, along with excess vapors expelled during engine running and refueling. If the hydrocarbon vapors do not remain contained and recycled, they can leak to the atmosphere, contributing to ozone pollution. A smog check, or emission control inspection, along with a code scanner, can determine a small or large EVAP system leak. A vehicle owner can use a smoke machine to pin-point the exact location of the leak and make the repair himself.
Things You'll Need
Code scanner (optional)
Trouble code book (optional)
Take your vehicle to a certified auto repair facility and have a technician hook up a code scanner to your vehicle. He will confirm that you have an EVAP emission control leak by looking up the trouble code. You can rent a code scanner from an auto parts store and perform your own scanner check. Hook up the code scanner to the universal jack under the dashboard and start the engine. If you find a trouble code displayed on the screen, write it down and look up the number in a trouble code book.
Place the vehicle transmission in "Park" for an automatic, and "Neutral" for a standard. Apply the emergency brake and raise the hood. Use a floor jack to lift the vehicle at both ends and place two jack stands under the front chassis frame, and two more under the rear frame. Slide under the vehicle, and check the fuel vapor vent hose that exits the fuel tank and runs along the chassis to the engine. The hose should have no cracks or sharp bends in it. Check the mounting bracket locations for scuffing or chaffing.
Refer to your owner's repair manual for the location of your EVAP system inside the engine compartment. Look for the charcoal canister, vent cap, vent solenoid, purge flow valve and EGR valve. Find the two small plastic lines that form a double port and attach near the vent cap. Remove the double port valve by pulling it off the nipples, which will leave two small holes in the port body. Attach an adapter cone, with hose, from a smoke machine to the top port hole, which should be the vacuum or intake manifold line.
Wedge a screwdriver in the throttle linkage to keep the throttle open. Turn on the smoke machine and let it pressurize the system for 2 to 3 minutes. If you see smoke coming out of the cold air intake hose, it means the system has pressurized. Use a strong flashlight to look at all the hoses, both large and thin, connected to the intake side of the emission control system. Check for small streams of white smoke coming from the hose connections and cracks in the hose. Once you find a leak, mark the hose with a piece of masking tape, so you can replace the hose.
Turn off the smoke machine and place the adapter cone into the lower double port hole. Turn the machine on and let the system pressurize. The lower port line will lead to the charcoal canister, so look for leaks in the line going to it and the connection points. Ignore the small amount of smoke emanating from the top of the vent cap -- this will be normal. Check high and low, all hoses, lines and connections. Tape any leaking hose with masking tape to identify the source of the leak. When finished, remove the smoke machine adaptor and hose and replug the double port back into the nipple connection.
Tips & Warnings
Many fuel tanks operate on as little as 2 psi pressure; always make sure the gas cap is fully tightened, to keep fuel vapors from escaping. A loose fuel cap can also trigger a trouble light, relative to the EVAP emission control system.