The tank will not build pressure. The vent valve is a normally open type, and the computer only closes it while it's running it's pressure check, otherwise it stays open to vent the tank. The reason I said to unplug the vent valve is so the computer doesn't even close it then, it's always open as it should be. The entire reason for the existence of the EVAP system is to prevent VOCs in the form of fuel fumes from escaping into the atmosphere. The amount we're talking about being "wasted" is negligible.
