GM Cadillac 1967-1989 Repair Guide

Evaporative Emission Control System

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OPERATION



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 reduced 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 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 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 forcing the existing fuel vapors back into the engine to be burned normally.

On 1981 and later V6s, the purge function is electronically controlled by a purge solenoid in the line which is itself controlled by the Electronic Control Module (ECM). While 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 and it 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 V6 canisters are of the Closed design, which means that the incoming air is drawn directly from the air cleaner.

SERVICE



See Figures 1, 2 and 3

The only service required for the evaporative emissions system is the periodic replacement of the charcoal canister filter (if so equipped). If the fuel tank cap on your car ever requires replacement, make sure that it is of the same type as the original.



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Fig. Fig. 1: Open canister evaporative emission control system (EECS) - this system is more common than the closed system



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Fig. Fig. 2: Closed canister EECS



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Fig. Fig. 3: Canister installation on the 1986-89 8-250 and 8-273 engine

CANISTER REMOVAL & INSTALLATION



All Engines Except 8-250
  1. Loosen the screw holding the canister retaining bracket.
  2.  
  3. Rotate the canister retaining bracket and remove the canister.
  4.  
  5. Tag and disconnect all hoses leading from the canister.
  6.  
  7. Installation is in the reverse order of removal.
  8.  

8-250 Engines
  1. Remove the relay center cover.
  2.  
  3. Remove the two relay center bracket bolts.
  4.  
  5. Remove the clip holding the canister purge lines to the relay center bracket.
  6.  
  7. Disconnect the electrical connectors at the canister and then position the center relay bracket away from the top of the canister.
  8.  
  9. Tag and disconnect all vacuum hoses at the canister; position them out of the way.
  10.  
  11. Remove the two canister mounting bolts and then lift out the canister.
  12.  

To install:
  1. Install the canister in the bracket as shown in the illustration.
  2.  
  3. Install the retainer and the two bolts.
  4.  
  5. Installation of the remaining components is in the reverse order of removal.
  6.  

FILTER REPLACEMENT



  1. Remove the vapor canister.
  2.  
  3. Pull the filter out from the bottom of the canister.
  4.  
  5. Install a new filter and then replace the canister as previously detailed.
  6.  

 
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