GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Evaporative Emission Control System

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OPERATION



See Figures 1, 2 and 3

The basic Evaporative Emission Control (EEC) system used on all models is the carbon canister storage method. The system is used to reduce emissions of fuel vapors from the car's fuel system. Evaporated fuel vapors are stored for burning during combustion rather than being vented into the atmosphere when the engine is not running. To accomplish this, the fuel tank and the carburetor float bowl are vented through a vapor canister containing activated charcoal. The system utilizes a sealed fuel tank with a dome that collects fuel vapors and allows them to pass on into a line connected with the vapor canister. In addition, the vapors that form above the float chamber in the carburetor also pass into a line connected with the canister. The canister absorbs these vapors in a bed of activated charcoal and retains them until the canister is purged or cleared by air drawn through the filter at its bottom. The absorbing occurs when the car is not running, while the purging or cleaning occurs when the car is running. The amount of vapor being drawn into the engine at any given time is too small to have an effect on either fuel economy or engine performance.

The Computer Control Module (ECM/PCM) controls the vacuum to the canister purge valve by using an electrically operated solenoid valve. When the system is in the "Open Loop" mode, the solenoid valve is energized and blocks all vacuum to the canister purge valve. When the system is in the "Closed Loop" mode, the solenoid valve is de-energized and vacuum is then supplied to operate the purge valve. This releases the fuel vapors, collected in the canister, into the induction system.

It is extremely important that only vapors be transferred to the engine. To avoid the possibility of liquid fuel being drawn into the system, the following features are included as part of the total system:



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Fig. Fig. 1: Operation of the 2.5L VIN R EEC system



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Fig. Fig. 2: Operation of the 3.1L VIN M EEC system



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Fig. Fig. 3: Operation of the 3.3L VIN N EEC system



A fuel tank overfill protector is provided to assure adequate room for expansion of liquid fuel volume with temperature changes.
 
A one point fuel tank venting system is provided on all models to assure that the tank will be vented under any normal car attitude. This is accomplished by the use of a domed tank.
 
A pressure-vacuum relief valve is located in the fuel cap.
 

Some canisters are of the closed design. They draw air from the air cleaner rather than the bottom of the canister.

REMOVAL & INSTALLATION



Vapor Canister

See Figure 4

  1. Loosen the screw holding the canister retaining bracket.
  2.  
  3. If equipped with A/C, loosen the attachments holding the accumulator and pipe assembly.
  4.  
  5. Rotate the canister retaining bracket and remove the canister.
  6.  



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Fig. Fig. 4: Common vapor canister

  1. Tag and disconnect the hoses leading from the canister.
  2.  

To install:
  1. Connect the canister, attach with the mounting bolts.
  2.  
  3. Attach the tagged hoses leading to the canister. Make sure the connections are correct.
  4.  

Filter
  1. Remove the vapor canister.
  2.  
  3. Pull the filter out from the bottom of the canister.
  4.  

To install:
  1. Install a new filter and then replace the canister.
  2.  

Evaporative Canister Purge Solenoid Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Some vehicles you will need to raise and support the vehicle.
  4.  
  5. Remove the electrical connection and vacuum line from the purge solenoid valve.
  6.  
  7. Some models will have the valve bolted in, remove the bolts to release the valve.
  8.  
  9. On other models, release the locking tab on the solenoid bracket, then remove the purge solenoid valve from the bracket.
  10.  

To install:
  1. Reinstall the valve by inserting the mounting bolts and tightening down, or install the valve to the bracket, then snap the valve down over the locking tabs of the bracket.
  2.  
  3. Connect the vacuum lines and electrical connection to the valve.
  4.  
  5. Lower the vehicle, if raised and supported.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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