Hi all....even though this issue has been beat it is time for a new twist on this old topic. In the process of trying to track down pressure building up in the gas tank I resolved to test every component in the vent process to the point of breaking open the cannister (which was easy and looked good). My last test found the problem and an unbelievable one it was. Under the fuse box in the frunk is a little line that goes to a pipe behind the gas pedal and then through the tunnel to the charcoal cannister in the rear passenger side. This pipe was clogged with some of the nastiest stuff I have ever seen in a pipe and it was very difficult to find because I had to cut the pipe to see what was going. Since this line is carrying lots of gas vapor it must have had bad gas, varnish, and gas additives accumulating into a solid mass throughout the line. It wasnt rust. It looked more like crystallized carbon, and gasoline products. This condition cause pressure to build up in the gas tank resulting in a loud whoosh when the cap was released. BE CAREFUL....determine if your tank is being overpressured by a blocked line or a vacuum is causing an inhale to the tank. Each has a different cause. If your tank is being pressurized I would bet money on the small vent tube to the cannister. You cant just replace the hose because the line may be completely blocke and it is not east to tell. Best way I found was to see if the air passes through the hose front to back. I attached some fun pictures but the solution is the hard one. Replace the line all the way back. I havent seen this problem described in detail before so have fun because I now have to replace the line to keep it stock.
