Here is a look...

 

Is that the ball down inside there? 4 door it should be in the filler neck, just like in the video.

 

No ball, just a trap door on a spring that moves smoothly when I poke it with my finger.

I removed the filler neck, there was no ball. There are no signs of this vehicle being changed either...

Looking online, there are others saying the "plastic" tanks like mine do not have a ball, but this door instead. I can't find anything wrong though, it seems to actuate smoothly?

 

I already put the neck back on, tried to get a picture though... Its through and through, I took all the hoses off and the neck out of the fender, there is /nooooothing/ inside any of this.

 

And a quick video.. so make sure we're on the same page here

All of what I removed and have put back, and where I'm at now...

https://www.amazon.com/clouddrive/sh...ink_copy_flash

 

The video above has a plastic tank as well, and should be very similar to yours. Something crazy going on here. This is a 2003 Blazer 4WD 4 door with a plastic tank correct?

 

That video is my tank a few minutes ago :P I took the video.

Yes, 2003 4 door blazer 4x4, the above video is my vehicle, right now, Wifi in the driveway

 

The filler... the vehicle, the view:

https://www.amazon.com/clouddrive/sh...ink_copy_flash

 

Does your fuel fill line enter the rear of the tank on a slight upward angle? In your video it's hard to tell.

 

Does not seem to, but give me a moment, going to get everything back together since its getting late and I think my air tools are going to be annoying some people soon...