GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Evaporative Emissions Control System


See Figure 1

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 vehicles, 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 1972-1976 vehicles, this service interval is 24,000 miles or 24 months. For 1977 and later vehicles, the mileage interval has been increased to 30,000 miles, while the time interval remains the same. Not all canisters contain a replaceable filter. During the mid-1980's, the use a canisters which are replaceable as a whole assembly began. For further details on the Evaporative Control System please refer to Driveability & Emissions Controls of this guide.

Click image to see an enlarged view

Fig. Fig. 1: Cut-away view of a basic evaporative emission charcoal vapor canister


  1. Tag and disconnect all vapor hoses which are connected to the charcoal canister.
  3. Loosen the retaining clamps or mounting bracket and then lift the canister from the vehicle.
  5. Grasp the filter in the bottom of the canister with your fingers, then squeeze and pull it out from under the lip surface or from under the retainer bar.

To install:
  1. Install a new filter to the bottom of the canister by squeezing and carefully inserting the filter into the canister. Make sure the edges are tucked under the canister lip.
  3. Position the canister assembly in the vehicle and secure using the retainers.
  5. Connect all vapor hoses to the canister as noted during removal.