Ford- Fairmount/Zephyr 1978-1983 Repair Guide

Fuel Evaporative Control System



Click image to see an enlarged view

Fig. Fig. 1 Common fuel and vapor line routing

Click image to see an enlarged view

Fig. Fig. 2 Typical vapor separator hose identification

Click image to see an enlarged view

Fig. Fig. 3 Fuel vapor separator hose-to-charcoal canister mounting

All Fairmont and Zephyr models are equipped with a fuel evaporative control system to prevent the evaporation of unburned gasoline. This system consists of a special vacuum/pressure relief filler cap, an expansion area at the top of the fuel tank, a foam-filled vapor separator mounted on top of the fuel tank, a carbon canister which stores fuel vapors and hoses which connect this equipment. The carburetor fuel bowl vapors are retained within the fuel bowl until the engine is started, at which point they are internally vented into the engine for burning.

The rest of the system functions as follows: change in atmospheric temperature causes the gasoline in the fuel tank to expand or contract. If this expansion and consequent vaporization take place in a conventional fuel tank, the fuel vapors escape through the filler cap or vent hose, and pollute the atmosphere. The fuel evaporative emission control system prevents this by routing the gasoline vapors to the engine, where they are burned.

As the gasoline in the fuel tank of a parked car begins to expand due to heat, the vapor that forms rises to the top of the fuel tank. The fuel tank is enlarged so that there exists an area representing 10-20% of the total fuel tank volume above the level of the fuel tank filler tube where these gases may collect. The vapors then travel upward into the vapor separator which prevents liquid gasoline from escaping from the fuel tank. The fuel vapor is drawn through the vapor separator outlet hose, then to the charcoal canister in the engine compartment. The vapor enters the canister, passes through a charcoal filter, then exits through the canister's grated bottom. As the vapor passes through the charcoal it is cleansed, so that the air that passes out of the bottom of the canister is almost free of pollutants.

When the engine is started, vacuum from the carburetor draws fresh air into the canister. As the entering air passes through the charcoal in the canister, it picks up the hydrocarbons that were deposited there by the fuel vapors. This mixture of hydrocarbons and fresh air is then carried through a hose to the air cleaner. In the carburetor, it combines with the incoming air/fuel mixture and enters the combustion chambers of the engine, where it is burned.

To solve the problem of allowing air into the tank to replace the gasoline displaced during normal use and the problem of relieving excess pressure from the fuel tank should it reach a dangerous level, a special filler cap was devised. Under normal circumstances, this filler cap functions as a check valve, allowing air to enter the tank to replace the fuel consumed. At the same time, it prevents vapors from escaping from the cap. In case of severe pressure within the tank, the filler cap valve opens, venting the pollutants to the atmosphere.


The only service performed on this system is the replacement of the charcoal canister.