i have an 2003 cavalier and most of the time when i pump gas in it the pump stop and fuel wont get into the car

thank you

 

This implies an issue with the evaporative emissions system, likely with the canister vent valve or the canister itself being full of gas, from over-filling when pumping gas. There is a vent tube from the fill neck down to the charcoal canister under the vehicle, and if you fill too high, by pumping AFTER the pump cuts you off, it can spill into that vent tube, filling it and the charcoal canister with gas. Once that happens, it becomes hard to fill the tank. It usually requires replacing the EVAP canister, the EVAP vent valve/solenoid, and possibly cleaning out the vent tube to the fill neck.

You can see the components of that system for your vehicle here:

https://charm.li/Chevrolet/2003/Cava...d%20Diagnosis/

Expand "Emission Control Systems" and "Evaporative Emission System".

The other option is something stuck in the filler neck, or it has become kinked somehow.