PeachParts Mercedes-Benz Forum - View Single Post

stevebfl · #3 07-17-2003, 08:17 AM

The charcoal cannister is the main component of the evaporative emissions system. This system is charged with holding all the vapor from the fuel tank system. Gasoline has a very high vapor pressure and readily evaporates. Unburned hydrocarbons are said to be the greatest not from the product of combustion anymore but from the fueling process and evaporative emissions.

Since way back the tank has had it top vent lines usually gathered into a liquid vapor seporator that returned condensed liquid back to the tank. When this was overcome (buy high heat and the sloshing of driving) the vent gases proceeded through a device called a rollover valve. It could hold the weight of gas in a rollover (1-2 psi if I recall - this is the limit to the pressure you feel when removing the cap).

From the rollover valve the fuel vapors entered the top of the charcoal cannister. The bottom was open to air but to get there the vapors had to pass over a lot of vapor eating charcoal. if this were the end of it then the charcoal would eventually be saturated with fuel and the vapors would proceed right through into the atmoshere.

So, the system continues by having a fixed or variable volume devise attached to the intake which now sucks air in at the bottom of the cannister over the charcoal and picks up the fuel vapors. They are carried into the engine in amounts planned to be insignificant to fuel management.

So to have raw fuel coming out of the canister the vent line has gotten into raw fuel. I would be sure of the routing of the fuel return lines. I would also verify the purge line from the canister to the intake.