I've got a probable EVAP system issue. My fuel tank builds up quite a bit of pressure when the car is running. When you take the fuel cap off all sorts of vapors come rushing out, you can even hear the sides of the tank thumping back in like a plastic bottle sometimes. The vapors are also pretty hot in temperature. There is a faint fuel smell when the car sits directly after running so I think the tank vent valve does actually work but I'm guessing the charcoal canister or tank pressure check valve could be the culprit?? Any similar experiences or good ways to diagnose this issue?? The engine is a 305 LO3 with a TPI conversion, not that that makes a difference since the EVAP system and tank are the same on each car. I just finished the TPI conversion about two months ago and all the parts on the fuel system are the same except for the Delco ep241 fuel pump. The car had some pressure in the tank before the swap but it is exponentially more now. Any suggestions??

 

A well documented problem

https://www.thirdgen.org/forums/tech...-pressure.html
https://www.thirdgen.org/forums/tech...-gas-tank.html
https://www.thirdgen.org/forums/carb...-pressure.html

 

Nice, thanks!!