Chevrolet Chevette/1000 1976-1988 Repair Guide

Evaporative Emission Control



The Evaporative Control System (ECS) limits gasoline vapor escape into the atmosphere. A domed fuel tank and pressure-vacuum filler cap is used with a plastic, charcoal-filled storage canister.

Fuel vapors travel from the fuel tank vent pipe (located above fuel level in the dome of the fuel tank), by way of steel tubing and fuel-resistant rubber hose to the plastic vapor storage canister in the engine compartment. Fuel vapors are routed into the PCV system for burning when ported carburetor vacuum operates a valve in the canister. As fuel is pumped from the tank, a relief valve in the tank cap opens to allow air to enter the fuel tank.


Charcoal Canister

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Fig. Fig. 1Before removing the charcoal canister, tag the vacuum lines to avoid confusion during installation

  1. Carefully note the installed position of the hose connected to the canister, then disconnect the hoses.
  3. Loosen the mounting clamps and remove the canister. To replace the canister filter, remove the filter from the bottom of the canister with your fingers.

Check to ensure that the hose connection openings are clear and check the purge valve by applying vacuum to it. If OK, it will hold vacuum. Check the condition of the hoses and replace as necessary. When replacing ECS hoses, use only fuel-resistant hose marked EVAP.

If the purge valve is defective, disconnect the lines at the valve and snap off the valve cap. Turn the cap slowly as the diaphragm is under spring tension. Remove the diaphragm, spring retainer, and spring. Check all orifices and replace parts as necessary. Install the spring, spring retainer, diaphragm and cap. Connect the lines to the valve.

  1. Install a new filter in the bottom of the charcoal canister.
  3. Install the canister and tighten its mounting clamp bolts.
  5. Connect the hoses to the top of the canister in their original positions.