GM Cutlass RWD 1970-1987 Repair Guide

Evaporative Emission Control System

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See Figures 1 and 2

OPERATION



This system, which was introduced on California cars in 1970 and other cars in 1971, 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 reduce vapor loss into the atmosphere.

The venting of fuel tank vapors into the air has been stopped by means of the carbon canister storage method. This method transfer 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 the 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 carrying the fuel vapors into the engine to be burned normally.



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Fig. Fig. 1: Tag and remove the lines, then loosen the retaining clamps



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Fig. Fig. 2: Remove the cannister from the vehicle

In 1981, the purge function on the 231 V6 engine was changed to electronic control by using a purge solenoid in the line. The solenoid itself is controlled by the Electronic Control Module (ECM). When the system is in the Open Loop mode, the solenoid valve is energized, blocking all vacuum to the purge valve. When the system is in the Closed Loop mode, the solenoid is de-energized, thus allowing existing vacuum to operate the purge valve. This releases the trapped fuel vapor which is forced into the induction system.

Most 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 231 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).

To determine if your vehicle has a cannister filter.

Remove the cannister from the vehicle and inspect the bottom of the cannister for a filter.

If the fuel tank cap on you car ever requires replacement, make sure that it is of the same type as the original.

The fuel tank cap on your car is designed to seal and hold pressure in the fuel tank. If the proper fuel cap is not used it may cause poor vehicle operation.

REMOVAL & INSTALLATION



Cannister & Filter
  1. Tag and disconnect all hoses.
  2.  
  3. Loosen the retainer clamps and lift out the canister.
  4.  
  5. Grasp the filter element and pull it out.
  6.  
  7. Replace the filter, then replace the canister, tighten the clamps and reconnect all hoses.
  8.  

 
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