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Fuel Vapor Canister...


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I've seen lots of posts on the old board talking about "smelling gas fumes". The answer usually mentions a "vapor canister" or filter. What does it look like and how do I find it? :o

The posts also mention the smell AFTER shutting the car off, but what about when you smell it just sitting at a red light? My bride doesn't even like to drive the car any more because of it. How do I tackle this?

Thanks again gentlemen.


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As I recall it is in the engine compartment over near/under the air cleaner assembly; but I can't remember if that was just the 4.9L or the NS. It looks like a vertical cylinder a few inches diameter.



Gasoline evaporates quite easily. In the past these evaporative emissions were vented into the atmosphere. 20% of all HC emissions from the automobile are from the gas tank. In 1970 legislation was passed, prohibiting venting of gas tank fumes into the atmosphere. An evaporative control system was developed to eliminate this source of pollution. The function of the fuel evaporative control system is to trap and store evaporative emissions from the gas tank and carburetor. A charcoal canister is used to trap the fuel vapors. The fuel vapors adhere to the charcoal, until the engine is started, and engine vacuum can be used to draw the vapors into the engine, so that they can be burned along with the fuel/air mixture. This system requires the use of a sealed gas tank filler cap. This cap is so important to the operation of the system, that a test of the cap is now being integrated into many state emission inspection programs. Pre-1970 cars released fuel vapors into the atmosphere through the use of a vented gas cap. Today with the use of sealed caps, redesigned gas tanks are used. The tank has to have the space for the vapors to collect so that they can then be vented to the charcoal canister. A purge valve is used to control the vapor flow into the engine. The purge valve is operated by engine vacuum. One common problem with this system is that the purge valve goes bad and engine vacuum draws fuel directly into the intake system. This enriches the fuel mixture and will foul the spark plugs. Most charcoal canisters have a filter that should be replaced periodically. This system should be checked when fuel mileage drops.

I am surprised that would cause fuel vapors in the passenger compartment though.


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Examine the fuel lines from the tank to the fuel rail. You may have a leak somewhere.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Evaporative Emissions Canister is located tucked up by the wheel well near the left muffler on my 94 STS. I am assuming this is what you're looking for. Mine is pretty cracked and I can see the filter, but I don't have a smell because of it's condition.

1994 STS Pearl White 260,000 KM (163,000 miles)

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per '97 service manual.

"Should the EVAP solenoid fail closed, electronicaly or mechanically, the canister charcoal bed could become saturated allowing vapors to escape to the atmosphere. The vapors should not enter the passenger compartment because of the rear mounted canister". I cannot find the location but I believe it is under the car near the fuel tank.

The canister appears to be rectangular in shape with two 1/4" nylon pipes (hoses) and one 5/16 pipe attatched to it via quick disconnects.

Checking the canister.

"Attatch a hose to the fuel vapor port (from fuel tank) to the canister and attempt to blow through it. Air should pass into canister. If not, replace canister".

"Attatch hose to EVAP port (from engine mounted solenoid) of the canister, and attemp to blow through it. Air should not pass into canister. If air passes, replace canister".

If the canister checks out ok then you will have to check the EVAP Solenoid "left hand rear of engine, on the cam cover, near the ignition coils" or the EVAP vacuum purge switch "left hand rear of engine, near the EGR valve. The proceedure for testing those is too lengthy to type. I'll have to scan them if you need them (when my daughter can show me how)

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B) Well, once again, this has proven to be the best site on the internet! As we say in East Texas, YOU CAN'T BEAT THAT WITH A STICK!

You can't get this kind of service in most restaurants.

Thanks a million... again!


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