A purge valve is used in any component that builds up water pressure, air pressure or vapour pressure. A automobile's purge valve is commonly called a canister purge valve. This purge valve -- part of the emissions system -- is used to release the build up of fuel vapours from the charcoal canister back into the engine so it can be recycled. A bad purge valve in a car can create multiple symptoms.
Engine Misses Out
When the canister purge valve is failing the engine often begin to miss out. The fuel vapours are building up inside the charcoal canister and pushing into the engine cylinders, causing the engine to choke. Because the purge valve is not releasing the fuel vapours back into the emissions system, the vapours are not recycled.
Failed Emissions Test
The canister purge valve will clog and prevent the recycling of the fuel vapours. These fuel vapours do not get sent back into the emissions system, causing the automobile to fail a state sanctioned emissions test. The release of harmful carbons are being released through the exhaust, causing the vehicle to fail the emissions test.
Once the purge valve fails, pressure builds up in the emissions systems causing the gaskets to blow open. Damaged gaskets will leak oil or, at worst, spray oil out onto the engine and engine compartment. This pressure is so intense that it breaks the tight seal the gaskets make and pushes through, creating oil leaks.
Damaged Spark Plugs
A good sign that the purge valve is not working is when the spark plugs go bad. Fuel is allowed into the intake system without being mixed properly. The fuel will be too rich, which causes the spark plugs to burn and wear prematurely. Since the valve is operated by a vacuum and releasing the build up of the fuel vapours is accomplished by the purge valve, a clogged or damaged valve does not allow the proper fuel mixture to enter the engine.