Chevrolet Citation/Omega/Phoenix/Skylark 1980-1985 Repair Guide

Evaporative Emission Control System

Print

OPERATION





Click image to see an enlarged view

Fig. Fig. 1 Typical open canister evaporative emission control system



Click image to see an enlarged view

Fig. Fig. 2 View of a closed canister evaporative emission control system



Click image to see an enlarged view

Fig. Fig. 3 The EVAP canister is located in the right front of the engine compartment

The basic Evaporative Emission Control System (EECS) used on all X-Body cars is the carbon canister storage method. This method transfers fuel vapors to an activated carbon storage device which absorbs and stores the vapor that is emitted from the engine's induction system while the engine is not running. When the engine is running, the stored vapor is purged from the carbon storage device by the intake air flow and then consumed in the normal combustion process. As manifold vacuum reaches a certain point, it opens a purge control valve atop the charcoal storage canister. This allows air to be drawn into the canister, thus forcing the existing fuel vapors back into the engine to be burned normally.

In 1981, the purge function on the V6 engine is electrically controlled by a purge solenoid in the line which is itself controlled by the Electronic Control Module. When the system is in the "Open Loop" mode, the solenoid valve is energized and blocks all vacuum to the purge valve. When the system is in the "Closed Loop" mode, the solenoid is de-energized and vacuum is then supplied to operate the purge valve. This releases the fuel vapors and it is forced into the induction system.

Most of the carbon canisters used are of the "Open" design, meaning that air is drawn in through the bottom (filter) of the canister. Some (1981 and later V6) canisters are of the "Closed" design, which means that the incoming air is drawn directly from the air cleaner.

SERVICE



The only service required is the periodic replacement of the canister filter (if so equipped). This procedure is covered in . If the fuel tank cap on your X-Body ever requires replacement, make sure that it is of the same type as the original.

 
label.common.footer.alt.autozoneLogo