GM: Electra/Park Avenue/Ninety-Eight 1990-1993

Fuel Evaporative Emission Control System

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Fig. Fig. 1 Evaporative Emissions Control System schematic



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Fig. Fig. 2 Representative vapor canister



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Fig. Fig. 3 Canister purge solenoid is mounted on the canister itself

OPERATION



The Evaporative Emission Control System is designed to prevent fuel tank vapors from being emitted into the atmosphere. When the engine is not running, gasoline vapors from the tank are stored in a charcoal canister, mounted under the hood. The charcoal canister absorbs the gasoline vapors and stores them until certain engine conditions are met and the vapors can be purged and burned by the engine. In some vehicles with fuel injection, any liquid fuel entering the canister goes into a reservoir in the bottom of the canister to protect the integrity of the carbon element in the canister above.

The charcoal canister purge valve cycle is controlled by the ecm through a solenoid valve on the canister. When the solenoid is activated, full manifold vacuum is applied to the top of the purge valve diaphragm to open the valve all the way. A high volume of fresh air is drawn into the canister and the gasoline vapors are purged quickly. The ecm activates the solenoid valve when the following conditions are met:



The engine is at the normal operating temperature.
 
After the engine has been running a specified period of time.
 
Vehicle speed is above a predetermined speed.
 
Throttle opening is above a predetermined value.
 

A vent pipe allows fuel vapors to flow to the charcoal canister. On some vehicles, the tank is isolated from the charcoal canister by a vapor restriction valve, located in the vapor line near the tank. It is a combination roll-over, integral pressure, and vacuum relief valve. When the vapor pressure in the tank exceeds 5kPa, the valve opens to allow vapors to vent to the canister. The valve also provides vacuum relief to protect against vacuum build-up in the fuel tank and roll-over spill protection.

Poor engine idle, stalling and poor driveability can be caused by an inoperative canister purge solenoid, a damaged canister or split, damaged or improperly connected hoses.

The most common symptom of problems in this system is fuel odors coming from under the hood. If there is no liquid fuel leak, check for a cracked or damaged vapor canister, inoperative or always open canister control valve, disconnected, misrouted, kinked or damaged vapor pipe or canister hoses; or a damaged air cleaner or improperly seated air cleaner gasket.

TESTING



Charcoal Canister
  1. Visually check the canister for cracks or damage.
  2.  
  3. If fuel is leaking from the bottom of the canister, replace canister and check for proper hose routing.
  4.  
  5. Check the filter at the bottom of the canister. If dirty, replace the filter.
  6.  

Canister Purge Control Solenoid
  1. Connect a clean length of hose to the fuel tank vapor line connection on the canister and attempt to blow through the purge solenoid. It should be difficult or impossible to blow through the solenoid. If air passes easily, the valve is stuck open and should be replaced.
  2.  
  3. Connect a hand-held vacuum pump to the top vacuum line fitting of the purge control solenoid. Apply a vacuum of 15 in. Hg (51kPa) to the purge valve diaphragm. If the diaphragm does not hold vacuum for at least 20 seconds the diaphragm is leaking. Replace the solenoid. If it is impossible to blow through the valve, it is stuck closed and must be replaced.
  4.  
  5. Unplug the connector and use jumper wires to supply 12 volts to the solenoid connections on the valve. With the vacuum still applied to the control vacuum tube, the purge control valve should open and it should be easy to blow through. If not, replace the valve.
  6.  
  7. Further, more in-depth electronic inspection can be performed using Chart C-3 later in this Section for your particular engine application.
  8.  

REMOVAL & INSTALLATION



Charcoal Canister
  1. Tag and disconnect the hoses from the canister.
  2.  
  3. Remove the charcoal canister retaining nuts.
  4.  
  5. Remove the canister from the vehicle.
  6.  
  7. Installation is the reverse of the removal procedure. Torque the retainers to 25 inch lbs. (2.8 Nm). If necessary, refer to the vehicle Emission Control Information label, located in the engine compartment, for proper routing of the vacuum hoses. If the label is missing, refer to the end of this Section to see if one of the labels given matches your engine.
  8.  

 
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