Gas cap won't stay sealed

I had a CEL come on today, and the code pointed to a loose gas gap. So I go to check the cap, and it doesn't feel right when I loosen it, no resistance. Screwing it back on sounds normal, it clicks, but when you unscrew the cap, it is very evident that it is not making a seal. I figured it was the cap, so I picked up a replacement real quick and that one did the same thing! So I think there may be something wrong or missing on my filler neck.

Here are some pic of the filler and cap, anything look out of place? The red arrow is pointing at the only thing that looks out of place, looks like some of the plastic may have broken? But it doesnt looks like the cap even touches that part.

https://i.imgur.com/n3UxwZ4.png
https://i.imgur.com/dsp9aYq.png
https://i.imgur.com/f3p5hQh.jpg

I had my frame replaced about a month ago, didn't have the truck on the road due to some other repairs that were needed until this week, so I am not sure when any damage may have happened.

 

Also, from digging around the web, it looks like there should be some kind of gasket on the cap? I am not sure what this part looks like or if I have it on my cap. I would have though the replacement would have come with any o-ring or gasket, and as I said, the new one had the same issue of not sealing.

https://i.imgur.com/MIOcwPs.png

 

Get an OEM cap, clear the code(s), drive it for a week or two. If the same code comes back it's likely the guys who swapped your frame forget to connect something at the charcoal canister/gas tank. Or they broke something, or maybe something just broke on it's own!

 

I will try an OEM cap. I cleared the codes already but expect them to come back soon since there is definitely an issue with the cap sealing. I might also see if I can find a gen 2 in the wild and take a peek at their cap/filler to see if there is a difference.

 

The cap should have 2 nubs sticking out from the outside of the white plastic "pipe". These nubs are 180 degrees apart. They go in the neck at 9 and 3 oclock. When you turn the cap, the nubs go behind the internal ridge.

 

Thanks for the pic, and yes my cap has those same nubs and looks pretty much exactly like that. Inside your filler, does this part of the plastic sit on any type of seal in the filler tube: https://i.imgur.com/iT9HSKC.png

 

Good luck with this. My dad's 4runner has had this issue for about 75k miles and we can't figure out the problem. Tried numerous gas caps from OEM to AutoZone to Oreillys.

I think the fix is to get a used filler neck from a wrecked vehicle.

By chance - do you have a habit of really tightening the gas cap after each fill up?

 

The filler neck is all metal. The rubber ring right below the arrow in your last pic is what does the sealing.

 

I have the same problem. I've tried 3 different OEM caps and still the same issue.

 

Lube the O ring occasionally with white grease and make sure the filler neck isn't rusting, a dab of grease ran around the sealing area prevents rust from starting.

I've done this for about 15 years now. I think the ethanol in gas now has made internal tank rust worse. [yeah the tanks are often plastic but the filler necks aren't.]