Very confused about this one, my 99 4dr Blazer 4.3 is leaking gas out of the vent valve above spare tire. It has to pass through the charcoal canister to get there. No codes being set. There seem to be pressure when you loosen cap.

 

If your EVAP canister is saturated with fuel, this can happen. The EVAP canister can get saturated with fuel if the tank is repeatedly topped off after the pump nozzle shuts off initially as well as if there is a problem with the EVAP system not pulling the fumes into the engine (purge solenoid). You will likely have to replace the EVAP canister.

 

I think that I will try a new Gm purge valve & canister. I have been afraid of installing a new canister and having it get soaked.

This is going to be pricey compared to what I did to the vent system on my 72 K/5. When I installed the new plastic tank I threw away a maze of rusted out lines. I then removed the filler neck and installed one from a 1969 with a vented cap.