exactly what does a charcoal canister do and is it really needed. i was driving on the freeway in my 70 chevelle i went over a pump and i heard this sound of kicking up sand. I looked in the rear mirror and recognized the bottom of my charcoal canister on the highway. I expected my car to to run strange but it ran exactly the same

The job of the charcoal canister is to collect the raw gas fumes and keep them contained until the engine can suck them into the combustion camber and burn them. This eliminates the fumes from going into the air.