kenmanme

I just bought a 2007 Tahoe LT, 5.3l 4WD. the truck runs great, but I can't get gas into the tank. It's the same issues as posted here and other forums, the pump shuts off after about one gallon. Based on other recommendations, I've replaced the evap canister vent valve, the purge valve solenoid, and the charcoal canister. I've blown compressed air through the vent line attached to the fill neck, seems clear. I even dropped the filler neck to check for obstructions, nothing there.
I've tried different positions of the gas pump nozzle, no effect. It happens at every station, every pump.
when I had the filler neck off, I noticed a plastic spring-loaded "baffle" just inside the fuel tank neck. I assume this might be the roll-over protection or something similar. The piece seems to move freely, but doesn't come all the way out of the tank..... I wonder if this could be the problem, but it does move in and out without trouble.

I have checked all the lines I can see and reach for kinks or bends, everything seems normal.
I must admit, when I went to replace the evap canister vent valve, it looked brand new..... certainly not original. I guess the previous owner had the same trouble and tried all the standard tricks and parts.....

No trouble codes present or in history

There has to be something I'm missing.... any other ideas?

tech2

what about the fresh air filter and line. air must be able to flow out the tank vent line, to the canister, out the normally open vent solenoid...out the fresh air line to the fresh air filter. Any blockages along this path will cause a hard fill.

I would remove the vent line from the cannister and try a fill...if its ok...everything towards the tank is clear...reconnect and disconnect at the cannister...ie keeping moving back untill you find the blockage. If its no good from the vent line...the problem is back to the tank

kenmanme

tech2, thanks for the response, but I have a few questions:
by fresh air filter and line, do you mean the flexible "corrugated" line from the evap can valve ? This line comes from the evap valve solenoid above the spare tire and ends in a small box with filter material inside it mounted above the back side of the gas cap. If so, that is all part of the replaced evap can valve, and it is not kinked or bent. Because it's brand new, it really shouldn't have any blockages.
I'd like to try removing the vent line from the canister as you mentioned and try a fill.......... I am assuming that the line to be disconnected is at the charcoal canister..... there are three lines attached there..... one goes back to the new evap valve solenoid above spare tire, one goes to the tank (it has a picture of a gas pump on it), and ones goes to the purge valve located in the engine compartment (at least I think it goes there). So I would remove the line with the gas pump picture and try a fill?
Can I blow air through this line back into the tank to check for blockages? Or will that cause other damage?
Thanks for your help...... this is really starting to get to me.

tech2

yep, that is the fresh air filtet line
yes, remove the line you stated and try a filled event

with this line off, you could try to remove the gas cap and blow through it from the cap in the normal flow...some vehicle has one way check valves to prevent the cannister from getting fuel saturated. evap smoke testers stay below 5psi of pressure so easy with the pressure....you just need to confirm airflow to the cannister line.
don't use an electrical motor to create your presssure.

kenmanme

Thanks again tech2... here's what i did:
i removed the line with the gas pump picture from the charcoal canister, removed the gas cap, and blew air through the line from the charcoal end. I was using a stand-alone air tank for this, pressurized to about 30psi, but I put on a regulator to limit the pressure coming out the hose to the lowest i could get it. A little bit of air at first, and it was heard coming out the filler neck . When I added a bit more air, it was still escaping from the filler neck, but i noticed the gas tank got pressurized a little. I then went to the gas station and tried to fill it up. Same issue as before, no noticeable improvement. While i was at the gas station, a guy with a 2009 Yukon was also trying to fill up. He said he had the same issue, but he could hold the nozzle a certain way and get the tank filled. He tried on my truck but no matter what position he put it in, the same thing would happen.
I went back home and tried to get some air into the tank by way of the filler neck, but I couldn't rig a suitable hose for a tight seal, so I couldn't tell if air was going all the way through to the vent line.
But, anyway, with the line disconnected form the charcoal canister, no difference in filling tank.

tech2

there is a hose off the filler neck. its purpose is to create a vacuum to suck vapours into the tank when refueling...it may also help shut off the fuel pump when the tank is full....make sure this small hose is clear.


https://www.carid.com/replace/fuel-filler-neck.html

kenmanme

yup,
when I had the filler neck out I inspected that rubber line, I could blow air through it from both ends, didn't seem collapsed or blocked. I also tried blowing air through the other end that goes to the tank, more of a hard plastic than rubber, that seemed clear as well. There is a disconnect near the tank on this line, so I might try just disconnecting it and try a fill. I'm willing to try anything at this point.

I was finally able to rig a hose to see what happens when I put air down the filler neck into the tank, as mentioned in a post above. When I did that, I could hear that spring-loaded plastic thingy inside the filler neck moving, but otherwise everything seemed ok.
Let's see what happens when I try a fill with the filler neck vent line off.

kenmanme

Well,
with the filler neck vent line disconnected, no difference in the fill up issue, although the dash flashed the "tighten gas cap" message pretty quick. It's curious I didn't get any DIC when other lines were disconnected.

tech2

that roll over ball in the tank you mentioned is the only other thing i can think of that would cause problems.

kenmanme

I just made things much worse....... the spring-loaded "flapper" thing inside the gas tank seemed to be the main problem, so I used a brass drift to push on it. It always seemed to be free, not stuck, but when I pushed on it with the brass drift, it fell inside the tank! There was no way I could retrieve it, but at least it was out of the way. I figured it might eventually impede the operation of the fuel pump or float (it if has one), but at least it shouldn't block the gas from entering the tank.
Thinking this was gonna do the trick, I went to the gas station and tried a fill up. The original problem was the gas pump would trip off after only a gallon or so. After pushing that thingy inside the tank, now the truck won't take any gas at all, it pukes it back out the filler neck almost instantly. It never did that before. Now I was really stumped. There did not seem to be any reason for this, since nothing appeared to be in the way of the fuel entering the tank.
Now the only way to get gas into the tank is by using a five gallon gas can and slowly put it in by hand.
Since the problem was much worse now, I had no choice but to drop the tank. I didn't want to do that myself, so I brought it to a mechanic friend. When they dropped the tank, they noticed that a previous owner had dropped the tank at sometime in the past and did not re-install a shield on top of the tank that protects the evap lines and fuel lines. Without that shield, when the tank was re-installed, all the lines above the tank got crushed between the tank and the underbody.

Even though I could blow air through all these lines, they were crushed enough to cause a problem with the tank venting properly. I decided to replace the tank and the molded hoses and lines all at once. Quite an expensive undertaking, but the problem is now solved.

For anyone else who has done all the recommended fixes for the gas pump tripping off during refueling and still has no luck, drop the tank and really inspect the hoses above the tank