Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Evaporative Emission Controls

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OPERATION



See Figures 1, 2, 3, 4 and 5

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Fig. Fig. 1: Evaporative emission system-1.2L,1.6L and 1.8L carbureted engines



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Fig. Fig. 2: Evaporative emission system-SPFI engine



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Fig. Fig. 3: Evaporative emission-MPFI engine



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Fig. Fig. 4: Cutaway view of an evaporative emission canister



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Fig. Fig. 5: Evaporative emission canister in the engine compartment-Legacy

The evaporative emission control system is employed to prevent evaporated fuel in the fuel tank or carburetor bowl (carbureted engines only) from being discharged into the atmosphere. System components differ slightly according to the model of the vehicle and the type of fuel system, but all systems function in the same manner.

Gasoline vapor from the fuel tank (and carburetor bowl) is introduced into a canister mounted in the engine compartment. This canister is filled with activated charcoal which absorbs the vapors and stores them. This function of the canister is continuous and is performed whether the engine is running or stopped; the function of the float chamber ventilation valve is only performed when the engine is stopped.

In order to clear the charcoal canister of vapors, the system purges the canister while the engine is running. When predetermined engine conditions are met, usually when the engine is at normal operating temperature and running at a speed greater than idle, a purge control valve opens to allow the stored vapors to enter the intake tract. The purge control valve can be vacuum or electrically controlled.

Once the purge control valve is open, the stored vapors in the canister are drawn, along with the incoming air/fuel charge, into the combustion chamber and burned. Fresh air is allowed to enter the canister through a filter in the bottom to fully purge the system.

Most models use a fuel separator, mounted on the fuel tank, to prevent liquid fuel from being transferred to the charcoal canister in the event of severe cornering or abrupt stops. Liquid fuel in the separator is returned to the fuel tank through a hose at the rear of the tank. On some models, a fuel cut valve is used to control liquid fuel from entering the vapor pipe. The rising level of the fuel from the tank causes a float to move up and close the cap hole to prevent fuel from entering the pipe.

A two-way valve is used on all vehicles to allow the fuel tank to breathe. When a vacuum is created in the fuel tank due to the fuel pump suck fuel, the two-way valve opens to allow a flow of air from the vapor canister to the tank. When pressure is built up in the tank, the valve opens in the opposite direction to allow the pressure to be vented into the charcoal canister. In the event of a two-way valve failure, the fuel cap is fitted with a valve to allow the tank to ingest air. This will prevent a collapse of the tank.

TESTING



There are several things which should be checked if a malfunction of the evaporative emission control system is suspected. These include deterioration of the vacuum lines, deteriorated, disconnected or pinched hoses, improperly routed hoses and/or a defective filler cap.

In the most severe cases of evaporative emissions system failure, the fuel tank may collapse. This condition is caused by a clogged or pinched vent line, a defective vapor separator, or a plugged or incorrect filler cap. The incorrect or faulty components do not allow the fuel tank to breathe and thus create a vacuum in the tank, causing it to collapse.

System Operation

Visually inspect the entire system for kinked, cracked, swollen, plugged or fatigued hoses. Replace the vapor canister if cracked, damaged or if fuel is leaking from the bottom.

Purge Lines and Canister
  1. Remove the fuel filler cap.
  2.  
  3. Disconnect the evaporation line at the evaporation pipe.
  4.  
  5. Check for an unobstructed evaporation line on the fuel tank side by blowing air into the hose. A little resistance should be felt due to the two-way valve.
  6.  

Take care not to suck on the hose as this causes fuel evaporation vapors to enter your mouth. This may cause serious injury.

  1. Check for an unobstructed evaporation line on the canister side by blowing air into the hose. A little resistance should be felt due to the two-way valve.
  2.  
  3. If an obstruction is found, remove the two-way valve and retest. If the obstruction is still present, clean or replace the line. If not, test the two-way valve and replace as necessary.
  4.  
  5. Check all lines for cracks or deterioration. Replace as necessary.
  6.  
  7. Check the exterior of the canister for damage and replace as necessary.
  8.  

Two-Way Valve
  1. Remove the two-way valve.
  2.  
  3. Check for air passage by blowing air into the lower nipple. A little resistance should be felt due to the functioning of the valve.
  4.  
  5. Repeat the test blowing into the upper nipple.
  6.  
  7. Check the valve case for cracks for deterioration.
  8.  
  9. Replace the valve if it fails any of the above tests.
  10.  

Float Chamber Ventilation Valve

This valve is used on carbureted engines only.

  1. Check the resistance between the positive and negative terminals. Resistance should be 16-20 ohms for the Justy and 32.7-39.9 for all other vehicles. If not, replace the solenoid valve.
  2.  
  3. Check the resistance between the Positive and negative terminals and the solenoid valve body. Resistance should be 1M ohm or more. If not, replace the solenoid valve.
  4.  
  5. Check the vacuum passage for opening and closing operation while applying electric current to both positive and negative terminals. If the vacuum passage fails to open when current is not applied or fails to close when current is applied, replace the solenoid valve.
  6.  

Fuel Filler Cap
  1. To test the filler cap, if it is the safety valve type, clean it and place it against your palm.
  2.  
  3. Blow into the relief valve housing.
  4.  
  5. If the cap passes pressure with light blowing or if it fails to release with hard blowing, it is defective and must be replaced.
  6.  

REMOVAL & INSTALLATION



Components of the evaporative system are all removed in the same basic manner. First label, then unplug any vacuum and electrical connections from the component. Remove any hardware retaining the component to the vehicle, then remove the component from the vehicle.

When replacing any evaporative emission system hoses, always use hoses that are fuel resistant.

Canister
  1. Label and disconnect the vacuum lines from the canister.
  2.  
  3. Loosen and remove the retainer screws holding the canister in place.
  4.  
  5. Remove the canister assembly from the engine compartment.
  6.  
  7. Inspect and replace any vacuum hoses that show signs of deterioration.
  8.  
  9. Inspect the canister for signs of damage and replace as required.
  10.  

To install:
  1. Install the canister into the retainer clamp, and tighten the screws.
  2.  
  3. Connect the vacuum lines.
  4.  

Two-Way Valve

The two-way valve is located on the fuel line, either near the fuel tank or in the engine compartment.

  1. On fuel injected vehicles, properly relieve the fuel system pressure.
  2.  
  3. Raise and support the vehicle safely on jackstands, and locate the two-way valve.
  4.  
  5. Loosen the hose clamps and slide them out of the way.
  6.  
  7. Note the direction of the valve, then disconnect it from the fuel lines.
  8.  


CAUTION
The valve will be filled with fuel. Take care not to spill the fuel into your eyes.

To install:
  1. Install the valve, making sure the flow direction is correct.
  2.  
  3. Install the hose clamps and tighten securely.
  4.  
  5. Lower the vehicle. Start the vehicle and check for fuel leaks.
  6.  

Float Chamber Ventilation Valve
  1. Tag and disconnect vacuum hoses attached to the float chamber valve.
  2.  
  3. Loosen the clamps, and remove the valve.
  4.  

To install:
  1. Check the condition of the vacuum hoses and replace as required.
  2.  
  3. Install the valve, tightening the hose clamps.
  4.  
  5. Attach the vacuum lines.
  6.  
  7. Start the engine and check for leaks.
  8.  

 
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