Still working on the old '85 30th Anniversary T-Bird. I changed the tank recently (all new tank, pump, filter). First time in 8 years the car had a full tank of gas run through without breaking the fuel system open somewhere (sat for 7 yrs... after engine repair ended up with routine filter changes... 3 per tank of gas!) After getting low on gas, I stopped to fill up and the tank was eiter pressurized or had vacum applied. I don't remember the car doing this before, and I thought the tank was supposed to be vented. Does this happen to anyone else? I live in TX, so I thought maybe it's pressure from the heat, but wouldn't it still vent through the charcoal tank up front? All the EGR stuff is still hooked up as original. Do I have a problem?
I believe they vent through a hose that runs up to the carbon canister near the engine. Its supposed to hold the vapors until the engine is running.
My cars frequently emit a "pshew" when i crack the gas-cap. If there is alot of pressure you might want to check your carbon canister and purge valve.