The likelihood of having a leak either from the fuel pump or tank sender access covers is much higher than a problem with the tank vent system. There is a rubber O ring in each of the access covers that will leak, along with the fuel tank filler grommet.
Fuel pressure in the tank is the result of the liquid gasoline vaporizing and creating pressure. It is managed by the Evaporative Emission Control system, AKA the carbon canister and canister vent solenoid.
The code 85 description explains how it operates.
Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.
Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. This reduces the tank pressure.
The canister is normally mounted on the passenger side frame rail near the smog pump pulley.
The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.
Purge valve solenoid:
The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister: