If your vehicle is showing gasoline spits back out of the filler neck when pumping gas, here are the most likely causes and the parts you'll need to fix each one.
Regularly 'topping off' the gas tank after the pump clicks off can force liquid fuel into the EVAP charcoal canister. This destroys the charcoal pellets and blocks the air vent path, causing pressure to push fuel back up the neck.
This valve is supposed to open to let air and vapors escape the tank while you pump gas. If it fails in the closed position or gets clogged with dust and debris, the trapped air forces fuel back out.
If the fuel tank or fuel pump was recently replaced, the filler hose or its parallel vent line may have been twisted, pinched, or kinked during reinstallation, physically blocking the flow of fuel or displaced air.
A mechanical flapper or check valve inside the filler neck (or at the tank inlet) prevents fuel from spilling during a rollover. If this valve jams shut, fuel cannot enter the tank and backs up immediately.