buttanic

I posted this in general tech also.
07 Suburban, I searched the forum and can't find a similar problem. No check engine light. Fuel tank is hard to fill. I checked the charcoal canister and it is not plugged,
I bypassed the vent valve completely and it still wouldn't fill. With lung pressure I am able to blow through the canister into the tank. When I do I hear bubbling in the tank like the vent line is below the fuel level in the tank which is between 1/2 and 3/4. How can this be possible. The vent line has to be above the fuel level for it to vent. Does anyone know how the vent is configured in the tank?

oilcanhenry

2007 Chevrolet Suburban Fuel Tank System Diagram



Yes the fuel vent to fuel nozzle insert should be located near the top of the fuel tank, so that the fumes are vacuumed or pushed out as fuel is added, out into the gas-fumes nozzle boot, if any, or to atmo, if not.

repairman54

On Express vans they put a louvered restrictor in the end of the metal fill pipe in between the rubber hoses. That stops siphon hoses and catches foreign objects.
Foil seals from additive bottle can get caught there also restricting gas going into the tank.
It will not show up on parts diagrams as it's not a separate part. I'm not 100% if it's in there on a Sub but I would check for it since it may be a standard GM thing.

oilcanhenry

I use locking gas caps on my vehicles to prevent fuel from being siphoned out, but also to keep anyone from dumping something down the tank that could cause damage to my engines. They used to make a cone-shaped spring device to keep fuel thieves hoses out, but nowadays, some thieves
just punch a hole in the lower fuel tank, and use a container to catch the fuel. I run wheel locks for the same reason: make them hard to steal. Yeah, I agree with you about the additive bottle foil seals. They have to come off all the way.

buttanic

Now that you mentioned this the flapper in the filler broke some time ago, I assumed it would go into the tank. It has been hard to fill for some time but got really bad a month ago long after the flapper broke but is worth checking out.

repairman54

I'll wager the flapper is stuck in the lover insert and blocking it. Pull out the metal pipe, #12, and take a look. You can leave the insert out since you may break it removing it.
Let us know how you make out.

buttanic

Update, all I found is this flake, which I believe is from a epoxy liner in a jerry can I was using for no ethanol gas for my generator during hurricane Ida and poured what I had left over into the Suburban. The screen is located in the rubber hose between the hard pipe and the tank. There was no sign of the flapper, obviously it couldn't have gone pass the screen into the tank. Side note there is check valve of sorts in the tank where the hose attaches. It seems to be free. I guess it is to prevent fuel going up the filler pipe under hard acceleration or going up hill. I haven't tried to add fuel yet as the tank is almost full. When I do I will post the result.

repairman54

That valve is called the rollover valve. Stops fuel from leaking out. I believe it's a fed. mandated thing.

buttanic

Update
It wasn't the flake on the screen in the filler line. My next thing is to try and disconnect the vent from the top of the tank and the purge cannister and blow towards the cannister. I can see it but it is in close quarters to work in. If that doesn't work the tank will have to come down.

buttanic

This solved the problem, the vent line from the top of the tank was full of carbon from the purge cannister. I wish someone can explain how carbon can get sucked into the vent line.