For starters, this is on a 2004 Cavalier.
This all started with not being able to put gas in the tank without the fill neck overflowing. I look under the car and I see gas leaking from the vent valve. I replace it with a new one and same thing.
Once I realized this system was only for vapor, I tracked the line from the vent valve to the charcoal canister. I detached the lines to the canister and poured a little more gas into fill neck and the same amount of gas poured out of the line from the tank that is supposed to be only vapor going into the charcoal canister. So it went right through. So obviously this issue is starting at the gas tank, with the fuel pump I assume.

So a few things. I never fill my tank, so its not from over flowing. I recently had to replace the fuel filter, but the lines going to the charcoal canister are all different sized connectors so there is no way I'm switching the lines. The gas gauge didn't work right after installing the new fuel filter(I'v replaced it on that car years ago and had no problems and did the same thing this time, so I'm pretty damn sure I didn't install anything wrong. Its just pulling the old one and droping in the new one really). Oh, and I replace the fuel filter like 3 months ago and the car has been working fine ever since, no fuel filling problems before this.

So I'm thinking its the cheap fuel pump doing something wrong here? I don't know what else it could be. With the gas gauge not working right from the get go, it seems suspect. Maybe some lines on the pump itself got crossed at the factory or something? But then why did I not have trouble filling the tank for 3 months? Unless there is something more in the tank than the fuel pump, I don't know how it couldn't be the pumps fault. If the pump isn't powered, it cant be pumping fuel out, so is there a valve on it that could have broke and is allowing fuel instead of vapor in?

 

My guess is the purge valve. The fuel pump isn't the problem. Can you check the purge valve solenoid for vacuum line integrity? Also you should be getting a check engine light

 

How could it possibly be the purge valve when I'v disconnected the entire evap system(the line from the tank is disconnected from the charcoal canister which leads to the vent valve which leads to the purge valve.) The purge valve cant be pulling gas out of the tank vapor line when its disconnected 3 parts removed unless I don't understand something fundamental here(which I might not honestly, thats why I'm here).

 

its not the purge.
cheap fuel pump? did you install a pump as there is no mention of it? did the problems start after a fuel pump replacement?

only thing that should come out of the tank vent line when filling is air/fumes.... if it only leaks fuel when filling and not when the pump is running.... i would drop the tank and inspect the port on the top of the tank that feeds the canister vent line... you will have to remove the pump module assembly to see inside the tank.

 

Yea, cheap fuel pump. It only leaks when I put in fuel, yes. If I pour a little shot in, a little shot will pour out of the tank vent tube instantly. I assume there has to be some sort of valve that isn't stopping the fuel from flowing up the vent pipe that is busted. I think when I pour into the tank, it makes a seal in the fill neck, then the pressure pushes the fuel up through the busted valve that is supposed to be stopping the fuel and only letting out vapor. I changed it(pump) out on this car about 5 years ago. I changed it most recently about 3 months ago and the problems started like 3 weeks ago. I could drop the tank out, I'm just not sure how to tell for sure its the pump once I have access to it. But yes, cheap pump and I'm pretty sure thats gotta be it. It runs fine by the way.

 

the pump has no connection to the vent...inspect the vent port. plastic or metal tank?

 

Plastic. What does the vent port connect to?

 

i looked up the fuel pump. the image does show the vent connection as part of the fuel pump module assembly/sending unit.
did you replace the pump only or the complete module; looks like you need a module assembly

More Information for PRECISE 402P3507M

 

Complete module. I didn't remember the vent tube going somewhere besides the pump, but I wasn't sure. I guess I'm going to drop the tank again. If there isn't anything obvious, you would have to agree its probably the pump as well? The gas gauge on the new pump wasn't working right from day one, and it was a 50 dollar pump I got from parts galaxy, so it wouldn't surprise me if I got a bunk one.(Thanks so much for your help by the way).