Hi, I have a 2021 Motorhome on a Chevy express van 3500 dually chassis with 6.6L engine and 30 gallon fuel tank

I've always had issues filling up the gas tank and the pump would shut off if the fuel pumped too fast. I have always needed to squeeze the pump just enough for a slower flow to not cause the fuel to splash back and turn off the pump.

Today I stick a borescope into the filler neck to see if there are any obstructions leading to the gas tank and I find this white cap with a small hole about a foot into the filler neck. This white cap doesn't look like a flap or a vent and it looks like all the fuel must go through the little hole which may be the cause of why the fuel pump stops so early while fueling.

First picture shows the white cap with a small hole inside the filler neck
Second picture shows the filler neck underneath the RV. The 11 inch mark is most likely where the white cap is located. Basically where the metal tube ends and where the black tube begins

I wanted to ask if any one knows what this white cap is? and if I take it out would it cause a check engine code to come?

 

I don't know the answer but that does seem like a small hole for all the fuel to pass through. I'm not sure why they would have such a restriction in the filler neck but I'm also not up on a lot of whats happening with newer vehicles either.

I don't see how it would affect pressure or vacuum in the tank so removing it probably wouldn't cause a CEL.

If I were forced to take a wild guess I'd say it was an anti-siphoning screen that didn't get all the holes punched in it or a plug to keep debris out during manufacturing and was supposed to be removed before assembly.

 

wow that makes alot of sense.
I'm going to take it out and hopefully it will be easy and wont cause any future issues

 

Let us know how it goes. I'm definitely curious about it.

 

Pulled it out of the filler neck and it was definitely the cause of my fueling issue.
I drove my motorhome to the nearest gas station and was able to fuel up to a full tank without the pump stopping. I wish I pulled this out so much sooner

I looked all around this "flap cap" for a part number and there isn't.
If any one knows what it's purpose is, please let me know. I don't think it is a anti siphon device because the flap seems large enough for a siphon tube to go through.
This Flap cap is spring loaded and the spring resistance increases the further back it is pushed open.
Although the resistance is light with my finger, I would imagine the force from fueling only opens the flap a quarter way. The housing of this flap cap also reduces the filler neck tube even more leading to the premature pump shut off I was experiencing.
This flap cap was most likely installed by the motorhome's manufacturer (Gulfstream) and not Chevrolet because the gas cap and filler neck is installed on the house section of the motorhome.

I hope this post helps anyone with a motorhome who is experiencing premature fuel pump shut off issues because I was about ready to buy and install a new charcoal canister and/or vent solenoid since the evap system is the leading cause of this fueling issue

 

I think this is some genius device to help reduce gasoline emissions when fuelling. I am not sure what life is like in the United States anymore, but it seems to me that up here in Canada as the price of gas increases, the slower the pumps pump gasoline. I rationalized that this waste of time and energy was simple psychology. Charge us more for gasoline and slow down the pumps so we feel like we get more for our money, when in all reality they are ripping us off blind. In expressing that opinion, I was corrected by a gas station owner. He said it was for emissions. To cut down on fuel vapors during fueling. You know, "Save the Environment".

Some ****er got paid for that device. If I had your camera I would check my fuel filler hose assembly too.

 

That is an anti rollover device in case of a rollover it wont let large amounts of gas flood out.

 

Anti rollover device to keep gas from flowing out in large amounts in case of rollover.