Can a bad gas tank filler neck cause an Eva leak, and also leak gas?


I got my car with a dead engine, it had about half a tank, since I didnt have the funds to get a new engine and all the necessary parts to fix/rebuild the car the car sat for a few months. Ever since I rebuilt the car and started driving it I have been getting super shitty mpgs(150 City) and close to 200miles(Highway) running 87oct, at I first I thought it was due to the fact that I had a bad O2 sensor and an exhaust leak which I corrected. After Correcting the O2 sensor I started to get an evap leak Cel. I checked the canister and I tried conducting some of the test the service manual suggest with no luck.

When I got the car it had it had a new aftermarket replacement gas cap, but I didnt give it to much tought and today while filling gas I realized that it lacks the little port that seals/secure the top of the filler neck. So now I am strying to figure out if this is the cause of the Evap code and if the neck is bad can it possibly leak gas?

 

Check the neck filler for holes, very common on these cars