Dodge Colt/Challenger/Conquest/Vista 1971-1989 Repair Guide

Evaporative Emission Controls



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Fig. Fig. 1 Schematic of an early model evaporative emission system

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Fig. Fig. 2 Common late model evaporative emission system

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Fig. Fig. 3 Vehicle emissions label located under the hood

This system is designed to prevent hydrocarbons from escaping into the atmosphere from the fuel tank, due to normal evaporation.

The parts of a typical system are: Separator tank: Located near the gasoline tank, used to accommodate expansion, and to allow maximum condensation of the fuel vapors. Canister: Located in the engine compartment to trap and retain gasoline vapors while the engine is not operating. When the engine is started, fresh air is drawn into the canister or canisters, removing the stored vapors, and is directed to the air cleaner. Vapor Check Valve: (1973-76) Used in the hose from the canister to the air cleaner to prevent vaporized fuel from entering the air cleaner during engine idling. Two-way Valve: (1977 and later) Because of different methods of tank venting and the use of a sealed gasoline tank cap, the two-way valve is used in the vapor lines. The valve relieves either pressure or vacuum in the tank. Purge Control Valve: (1977 and later) The purge control valve replaces the check valve used in previous years. During idle, the valve closes off the vapor passage to the air cleaner. Fuel Check Valve: (1976 and later) This valve is used to prevent fuel leakage in case of roll over. It is installed in the vapor line between the two-way valve and the canister on the coupe, sedan, and hatchback, and between the separator and the two-way valve on the station wagon. Bowl Vent Valve: (1980 and later) Controls carburetor bowl vapors between canister and carburetor. Carbon Element: (1980 and later) Element is located in the air cleaner to store vapors generated in the carburetor. Replace if clogged or dirty.


Be sure that all hoses are clamped and not dry-rotted or broken. Check the valves for cracks, signs of gasoline leakage, and proper operating condition.

The canister air filter should be inspected and changed at least every 24,000 miles.


Charcoal Canister
1971-72 MODELS
  1. Loosen and remove the two purge valve retaining bolts. Leave the hoses attached to the valve.
  3. Loosen the purge valve-to-canister hose clamp at the canister and pull off the hose.
  5. Loosen the expansion tank-to-canister hose clamp at the canister and remove the hose.
  7. Remove the two canister bracket bolts and remove the canister.
  9. Install the canister and connect the hoses.


The canister or canisters used on these models is replaced periodically. No other maintenance is necessary except for an occasional check of connecting hose condition. To replace the canister:

  1. Remove the two connecting hoses from the canister.
  3. Loosen and remove the canister retaining band bolt.
  5. Remove the canister.
  7. Install the canister and connect the hoses. Replace any brittle hoses.