I have a situation/question with my gas tank that im not sure if anyone else ever experienced....about a month or 2 ago i was getting gas and by accident i grabbed the diesel hose which was on the same pump as regular gas, obviously it doesn't fit in but at first i kinda pushed it a little harder than you should have to because i just assumed it should be going in. i realized it was the wrong hose, grabbed the other hose for gasoline and filled up as usual. im not sure if it happened right away or the next day, but CEL goes on. i check the code it was the evap/gas cap code, so i figured i didn't tighten the cap so i cleared it and made sure cap was tight. well the light comes back on again soon after that, and i just ignored it knowing i would have to get it checked or buy a new cap.

so the next time i get gas something doesn't look right to me, there was no little metal cover over the hole the gas hose goes into. i'm not 100% sure but there is supposed to be a little cover there right? which leads me to believe that it broke off somehow, maybe when i grabbed the diesel hose. so my question is, does this sound coincidental or would that have an effect on how the gas cap seals? i was going to just buy a new cap and try it but just haven't got around to it yet, but now car is due for emissions inspection this month and it will need to be fixed.

i know i can try a new cap, i could have it smoke tested, but somethings telling me that the problem may be related to the that little piece thats missing. any ideas before i just start buying parts or paying for tests? thanks in advance for any help or ideas

 

That plate in the throat of the filler tube is an attempt to prevent you from putting in the wrong kind of fuel. The nozzles for the different kinds of fuels are different diameters, the unleaded fuel nozzles being the smallest.

It is just a metal plate. It doesn't have any sensors or things attached to it. If it were to get knocked out and somehow make its way into the gas tank, it would just lay there like a piece of dirt.

When you were forcing the diesel fuel hose, I wonder if you might have somehow warped the opening to the filler neck so that it is no longer perfectly round.

 

Did you only get a single code? When I had an EVAP leak I got 2 codes, one was for large EVAP leak. Yes the first thing is the fuel cap to check, see if the rubber seal is damaged, look at the filler neck surface for any irregularities. Smear some grease on the seal to held seal it and try again. You may have distorted your filler neck sealing surface, but it is pretty tough.
In my case I had to go for a smoke test, it found my leak was my charcoal canister......I had a tiny exhaust leak in my resonator, and the charcoal canister is mounted right above the resonator, and there was a tiny stream of hot exhaust aimed directly at the plastic charcoal canister and it melted a hole in it.