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Slow Fuel Tank Fill
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Question
FuzzyDriver
I have a 2004 4x4 GMC Sierra short-bed with the most annoying problem. My truck has 54000 miles and only got this particular problem a month or so ago.
Problem: I can only put about .3 gallons in the tank before the automatic nozzle trips off. If I restart immediately then it trips immediately. If I wait a while I can put in another .3 gallons or so before it trips.
It takes FOREVER to fill the tank this way. I noticed that if I listen I can hear the sound of air coming from the filler pipe. When the tank is VERY low (almost empty) I can put in about 1.2 gallons before the first trip; after that it's .3. Logically, this tells me that (1) the filler must extend into the tank to nearly the bottom, allowing it to vent until the level reaches that point and (2) my filler pipe holds about .3 gallons. It also tells me that the vent is not venting, or is venting VERY slowly.
I disconnected the vent tube at the top of the filler pipe. Inside was a small brass flow constrictor. I removed it. This helped reduced the time I have to wait between .3 gallon fills, but not much.
While I was mucking about under my truck, I tried to draw a vacuum on the vent tube with a small vacuum tester. I could not draw a detectable vacuum at that slow hand-pump rate.
Next I tried my air compressor. Air flowed readily into the (nearly empty, ~ 2 gallons left) tank and began pressurizing the tank. It seems I could even hear the tank expanding. When I took the air compressor off, the air came back out kind of at the rate you can blow through a soda straw. No gas or air came out of the open vent tube at the top of the filler (I had not blocked it, which seems stupid now in retrospect as I was looking right at it). Shouldn't I have gotten a face full of gas?
Then I tried blowing air into the vent fitting. Air came right out of the vent, the tank did not pressurize.
What's going on? I need to put gas in this puppy once in a while!
I had P0442 and P0446 for about a year before this happened. Reset them a couple weeks ago during my troubleshooting efforts and no codes of any kind have reappeared (although from what I understand I haven't met the conditions for those two tests to be run, anyway).
Also, my Haynes manual says there is a sticker showing the EVAP system on the radiator support, but it isn't there. There's a flat spot when another sticker could have gone.
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