Rotary Car Club - View Single Post - What's the prurpose of the charcoal canister?

Pete_89T2 · 04-13-2011, 08:35 AM

I would leave the charcoal canister alone; removing it buys you nothing WRT more power or reliability, but doing the bypass will result in a stinky fuel vapor smell under the hood. It doesn't weigh all that much or take up too much space, and since it's a passive device it's very reliable - I've never heard of one these things failing - ever.

These "evaporative emissions" systems have been in cars in the US since the late '60s/early 70's. Before that time, gas tank caps simply vented straight to atmosphere, allowing any fuel vapor pressure that builds up in the tank to escape. To reduce pollution from those gas vapors, the automakers changed the gas caps to sealed designs that don't vent. Your FC has a sealed gas cap. To deal with the vapor pressure that still builds up in the tank, they plumb it to the canister for what amounts to temporary storage. When your car is running, the line that connects to the engine will suck any built-up vapors stored in the cansiter into the combustion chambers to be burned. When the car is NOT running, the volume of the canister alone is typically sufficient to trap all the vapors your fuel tank produces, BUT if it's hot OR the gasoline in your tank has a higher than usual vapor pressure, that's where the charcoal comes into play.... The charcoal absorbs most of the hydrocarbon molecules present in the fuel vapor, allowing the excess pressure to safely vent to atmosphere minus the hydrocarbon pollutants and that stinky fuel smell. Think of it as a chemical one-way check valve.

04-13-2011, 08:35 AM	#7
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD Posts: 874 Rep Power: 16	I would leave the charcoal canister alone; removing it buys you nothing WRT more power or reliability, but doing the bypass will result in a stinky fuel vapor smell under the hood. It doesn't weigh all that much or take up too much space, and since it's a passive device it's very reliable - I've never heard of one these things failing - ever. These "evaporative emissions" systems have been in cars in the US since the late '60s/early 70's. Before that time, gas tank caps simply vented straight to atmosphere, allowing any fuel vapor pressure that builds up in the tank to escape. To reduce pollution from those gas vapors, the automakers changed the gas caps to sealed designs that don't vent. Your FC has a sealed gas cap. To deal with the vapor pressure that still builds up in the tank, they plumb it to the canister for what amounts to temporary storage. When your car is running, the line that connects to the engine will suck any built-up vapors stored in the cansiter into the combustion chambers to be burned. When the car is NOT running, the volume of the canister alone is typically sufficient to trap all the vapors your fuel tank produces, BUT if it's hot OR the gasoline in your tank has a higher than usual vapor pressure, that's where the charcoal comes into play.... The charcoal absorbs most of the hydrocarbon molecules present in the fuel vapor, allowing the excess pressure to safely vent to atmosphere minus the hydrocarbon pollutants and that stinky fuel smell. Think of it as a chemical one-way check valve.