Hi there,

i own a 1990 pontiac trans am with a 5.0 tpi. when we were getting gas for the car we noticed a loud "whooooosh"when we took off the gas cap. i was wondering if that was normal on these cars or not. i do know that there is a pressure release valve, but it seemed like a lot of pressure was released. it almost seemed like too much.

 

Normal.

JamesC

 

Tank pressure is definitely normal unless like mine was. Mine was releasing pressure through gas cap while I drove it and or after I turned it off which I thought was excessive. I investigated and found my vapor purge valve was installed backwards and wasn't allowing anything to pass to canister in engine compartment. Also there is a tank vent valve located under rear axle driver's side that could cause excessive pressure.So if your cap is only releasing pressure when you open it you should be ok, TPI systems I am told do have more pressure than other type of systems.