DOHC ZC in my 89 hatch, my question might be dumb but now that it is getting hot outside I'm noticing that when I go to refuel my car there is a ton of air being sucked in when I unscrew my gas cap. I realize why air get sucked in to the tank because of the gas displacing the air when returned to the tank, but I've noticed it's like a good 15 sec hissing sound (I unscrew it slowly). When it was cold it did it here and there now that it's 80+ out it is every time. I filled the tank to full the other day and then it got hot and leaked out down the side of my car because of the pressure. Just curious if this is normal because I've never had a car with this much pressure in the tank. May be a dumb question but I'm sure you all will give me some info. Thanks

 

Its normal.

 

That is not normal. lol

There are a few pieces of equipment that control air flow within the fuel tank. The charcoal canister is the primary suspect, as this device allows the tank to breathe while the car is running or not and allows draft air over the fuel in the tank. The purge solenoid valve opens and exposes the fuel tank to manifold vacuum that is pulse modulated, controlling vapor pressure in the tank.

The canister contains activated carbon pellets that will smash up over time, or ingest dirt from the vent line that begins to clog the vent on top of the canister, preventing the tank pressure from equalizing.

Failure to address this problem can result in manifold vacuum collapsing or severely damaging the fuel tank to the point where it can begin to leak. Fuel pump failure can also be hastened by this as the vacuum in the tank fights the pump.