Chevrolet Full-size Cars 1968-1978 Repair Guide

Evaporative Emissions Control System



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Fig. Fig. 1 Common evaporative canister

This system, standard since 1970, eliminates the release of unburned fuel vapors into the atmosphere. The only periodic maintenance required is an occasional check of the connecting lines of the system for kinks or other damage and deterioration. Lines should only be replaced with quality fuel line or special hose marked evap. On the 1970-71 cars, every 12,000 miles or 12 months, the filter in the bottom of the carbon canister which is located in the engine compartment should be removed and replaced. On 1972-76 cars, this service interval is 24,000 miles or 24 months. For 1977-78 cars, the mileage interval has been increased to 30,000 miles, while the time interval remains the same. For further details on the Evaporative Control System please refer to .


  1. Tag and disconnect all hoses connected to the charcoal canister.
  3. Loosen the retaining clamps and then lift out the canister.
  5. Grasp the filter in the bottom of the canister with your fingers and pull it out. Replace it with a new one.
  7. Installation of the remaining components is in the reverse order of removal.