Quote Originally Posted by Rustam View Post
carbon in the charcoal canister gums up? not sure if youre confusing this one with the carbon buildup from combustion. I dont believe carbon in the charcoal canister gums up, given own experiements in blowing through the canister that was god knows how old. If that gums up then it should block entry of air into the gas takn, and subsequent implosion due to negative pressure from dropping fuel level. most certainly that effect should be alleviated by the intermittently opening EVAP valve, but through the years some deformation of the gas tank should be evident.
Sorry, I wasn't clear- I didn't mean gummed as in blocked, just that the carbon de-activates due to pollutants from the fuel, so no longer does its job. In that case people start smelling petrol around the car, which causes problems at the Dealers, so they have to prevent it happening. For this reason the canister is a common wear item, and IIRC is replaced in some places to meet regulations or service intervals, or if it stops working. I replaced one on my old 535i because it was getting smelly once left to heat soak on a hot day, and not idling properly in warmup. That was all down to the valve though. It's amazing how long a canister can last.