GM Corvette 1963-1982 Repair Guide

Evaporative Emission Control (EEC) System



1970-81 Vehicles

See Figure 1

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Fig. Fig. 1: View of the charcoal evaporative emission canister on a 1979 Corvette

Introduced on California cars in 1970, and nationwide in 1971, this system reduces the amount of escaping gasoline vapors. Float bowl emissions are controlled by internal carburetor modifications. Redesigned bowl vents, reduced bowl capacity, heat shields, and improved intake manifold-to-carburetor insulation serve to reduce vapor loss into the atmosphere. The venting of fuel tank vapors into the air has been stopped. Fuel vapors are now directed through lines to a canister containing an activated charcoal filter. Unburned vapors are trapped here until the engine is started. When the engine is running, the canister is purged by air drawn in by manifold vacuum. The air and fuel vapors are then directed into the engine to be burned. This system is designed to reduce fuel vapor emission. The canister filter should be replaced every 12 months or 12,000 miles on 1970-74 vehicles, on 1975-81 vehicles the interval is extended to 24 months or 30,000 miles.

The filter is located in the bottom of the canister. To replace the filter, pull out the old filter and work the new filter into place. It may be necessary to remove the bottom of the canister for access.

1982 Vehicles See Figures 2, 3 and 4

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Fig. Fig. 2: Schematic of the evaporative emission control system-1980 vehicle shown, others similar

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Fig. Fig. 3: Location of the evaporative canister-1982 vehicle shown

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Fig. Fig. 4: View of the evaporative canister components

The EEC system for 1982 vehicles performs the same function as the earlier system, but uses a purge control solenoid which is installed in the vacuum line between the charcoal canister and the PCV valve (mounted on the driver-side fender, under the hood). The ECM of the computerized emissions system controls the action of the purge control solenoid. Depending upon various conditions of operation, the ECM will either energize or de-energize the solenoid. When the solenoid is energized, vacuum is not available to draw fuel vapors from the canister; when de-energized, vacuum draws the canister vapors into the intake tract of the engine. The solenoid is mounted on the drivers-side fender, inside the engine compartment. Replacement of the solenoid is simply a matter of tagging and disconnecting the hoses and wiring from the solenoid, and unbolting the solenoid.