Quote:
Originally Posted by Contender
Hmm or cheaper yet why not just pull it all out. Its not really needed.
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I would expect to get many error codes if you tried that.
The evap system is tied in to many emissions requirements. I spent a year as an engineer doing cannister purge valves (controls the flow in the evap system).
Basically on a hot day you get a buildup of vapour in your gas tank. Instead of venting toxic vapours to the atmosphere (and wasting gas) it goes to the charcoal canister where it waits to be used. Every so often the ECU will crack open the CPV and 'have a sniff' to see if there's much gas in there. If there is the computer will open the valve (modulate via duty-cycle) and vary the fuel amount accordingly. Sitting at a street light on a hot day your engine may in fact be running solely based on vapours from the charcoal cannister.
When you overfill the tank then you get liquid fuel in the charcoal cannister. Eventually it evaporate and go through the engine so if you don't do it too often or too much then it's ok.