I keep getting the "tighten fuel cap" error alert. I used to have the problem of not able to fill gas tank. I have replaced the evap at the rear of the vehicle, the charcoal canister (blew out all the beads) and the one at the engine (dont remember the name of it). All this fixed my fuel fill problem. I also replaced the gas cap with an ac delco one. I put a smoker on it and the only place smoke comes out is at the rear evap (I think this is normal??). Assuming the smoke is supposed to come out the evap with engine off (I tried with key on as well) than I am at a loss on what to check next.