The check valve in the cap allow fresh air in, to prevent vacuum in the tank. The valve on the charcoal canister and TVV (thermal vacuum valve) or BVSV (bimetal vacuum switching valve) on later model release positive pressure from the tank. Check that if it is clogged. The TVV (and BVSV) is on water neck.
Also, under the charcoal canister, there is another check valve that release air from the canister. Check that too.
Wednesday, October 15th, 2008 AT 10:42 PM