am i supposes to have pressure inside the gas tank? cause my truck never has that pressure when u open the gas cap

 

It's not necessarily noticeable when you open the gas cap.

 

i have fumes coming from the top of the tank am lowering the tank tomorrow to check for leaks

 

The tank is supposed to be under vacuum as part of the evap emissions control system.

 

so what should i look for? itsmell really bad under the car