Help! O6 impala

i have a 06 impala and i had to have my waterpump replaced...when it left the dealership my car told me to tighten gas cap...so i did...i eventually bought a new one and nothing went away..I took it in and they told me the engine light code was a large evap leak and the problem was the "purge solynoid valve"..had that replaced and nothing was fixed!! Someone help please

hi a large evap leak means the gas tank isn't building any pressure and a valve stuck or a plastic line is broken.The dealer should've put a evap vapor machine on it to tell where it leak is coming from before they changed anything.My suggestion would be not to ever go back to that dealer they are just screwing you over.There is only a few spots you can have leaks. The purge valve that you mentioned you changed, then there the gas cap you said you changed too(but the question is are you filling your gas tank with the car running?)that will trigger that code too. Then there is the charcoal canister might have a crack in it. And the final vent valve stuck open.But when you paid the big money to the dealer to check it out they shouldve use the evap ultravoliet check machine to find the problem. If they didn't they are not a mechanic.I bet they cracked a line changing your water pump or you are filling the tank with the car running.One of those 2 for the large evap code to trigger.hope it helps.What engine you got in that 3.5l 3.9l or 5.3l?is it a p0455 code? there does seem to be any technical service bulletin tsb or recalls on it. So that is a good sign your charcoal canister isn't a problem.if you take it to a local mechanic ask if they have a evap vapor machine before they look at it. If they don't run away from there every good mechanic has a vapor machine. If they don't they are playing the i guess this is the part ,replace it and drive it 60 miles and see what happens game.