I have a co-worker that has a 2001 Chevy Silverado 4.8 engine. The gas tank builds pressure after driving 5 or 10 miles or less?
He has changed the fuel pump, filter, three gas caps, e-vap canister, and cleaned the fuel line from the canister to the tank. When removing the gas cap it release a lot of air?
He also has talked with a mechanic and our county fleet guy. Any ideas whats happening here?

 

It should have a code set for a valve fault or EVAP fault.

I would check the purge valve.

 

Thanks, We will check it out.

 

Thanks, We got Codes

P040 - EVAP system
Code - P0452 - Tank Pressure Senor.

 

That's the sensor mounted on the top rear of the tank, I think. If it's buggered the engine will never attempt to pull vacuum on the tank.

 

GM Has a retro fit for the EVAP Purge solenoid, its relocates it forward and higher out of the way of junk. With a good scan tool you can manually open and close purge valve. I would start with that, bet its stuck closes.

Usually purge vlave is located at rear of tank of side, but thye like to move them around

 

 

Thanks, I'll post back what we find.