Toyota Celica 1994-1998 Repair Guide

Evaporative Emission Controls

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OPERATION



See Figures 1 and 2

The Evaporative Emission Control (EVAP) 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. 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, 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. These systems employ the following components:



Charcoal canister
 
Fuel tank cap
 
Thermal Vacuum Valve (TVV)
 
Check valve
 
Heated Oxygen sensors
 



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Fig. Fig. 1: Evaporative Emission Control (EVAP) system components-5S-FE engine



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Fig. Fig. 2: Evaporative Emission Control (EVAP) system components-7A-FE engine

COMPONENT TESTING



See Figure 3

Before embarking on component removal or extensive diagnosis, perform a complete visual check of the system. Every vacuum line and vapor line (including the lines running to the tank) should be inspected for cracking, loose clamps, kinks and obstructions. Additionally, check the tank for any signs of deformation or crushing. Each vacuum port on the engine or manifold should be checked for restriction by dirt or sludge.



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Fig. Fig. 3: Always inspect the lines for kinks, cracks and loose connections

The evaporative control system is generally not prone to component failure in normal circumstances; most problems can be tracked to the causes listed above.

Fuel Filler Cap

See Figure 4

Check that the filler cap seals effectively. Replace the filler cap if the seal is defective.



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Fig. Fig. 4: Inspect the gasket on the fuel cap, if deteriorated, replace the gasket or cap as necessary

Charcoal Canister

See Figures 5, 6, 7 and 8

  1. Remove the charcoal canister from the vehicle.
  2.  
  3. Visually check the charcoal canister for cracks or damage.
  4.  



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Fig. Fig. 5: Visually check the charcoal canister for cracks or damage-5S-FE other engines similar

  1. Check for a clogged filter and stuck check valve. Using low pressure compressed air (0.68 psi. or 4 kPa), blow into the tank pipe B and check that the air flows without resistance from the other pipes. Next, blow air into port B and check that air does not flow from any other port. If this does not test positive replace the canister.
  2.  



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Fig. Fig. 6: To check for a clogged filter or check valve, blow compressed air into the pipe A ...



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Fig. Fig. 7: ... next, blow air into port B and check that air does not flow from the other ports

  1. Clean the filter in the canister by blowing no more than 43 psi (294 kPa) of compressed air into the pipe (A) to the outer vent control valve while holding the other upper canister pipes B closed.
  2.  



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Fig. Fig. 8: To clean the filter blow compressed air into port A while holding port B closed

Do not attempt to wash the charcoal canister. Also be sure that no activated carbon comes out of the canister during the cleaning process.

  1. Replace or reinstall the canister as needed.
  2.  

Thermal Vacuum Valve (TVV)

See Figures 9, 10 and 11



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Fig. Fig. 9: The Thermal Vacuum valve (TVV) is always located in the water housing on these models

  1. Drain the engine coolant.
  2.  
  3. Remove the TVV valve from the water housing.
  4.  

Be sure to label all hoses leading to the valve.

  1. Cool the valve to below 95-104° F (35-40° C) with cool water.
  2.  
  3. Make sure that air does not flow from the upper port to the lower port.
  4.  



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Fig. Fig. 10: Inspecting TVV operation in cold water

  1. Heat the TVV to above 129° F (59° C) with hot water.
  2.  
  3. Check that air flows from the upper port to the lower port of the valve. If the operation is not as specified, replace the TVV valve.
  4.  



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Fig. Fig. 11: Inspecting TVV operation in hot water

Check Valve

Some check valves are made with two ports and others with three. The two port valves are yellow and black, the three ports are yellow and white.

2 PORT

See Figures 12, 13 and 14

  1. Label and remove the check valve.
  2.  



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Fig. Fig. 12: Remove the two-port check valve

  1. Blow air into the yellow port. Check that the air flows from the yellow port to the black port.
  2.  



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Fig. Fig. 13: Blow air into the yellow port and check flow from the black-2 port

  1. Blow air into the yellow port and make sure air does not flow from the black port.
  2.  
  3. Install the check valve with the yellow port facing the body side.
  4.  



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Fig. Fig. 14: Make sure the check valve is installed correctly, yellow side facing the body

3 PORT

See Figures 15 and 16

  1. Label and remove the check valve.
  2.  
  3. Blow air into the yellow port. Check that the air flows from the yellow port to the white ports.
  4.  



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Fig. Fig. 15: Test the air flow for each port on the check valve-3 port

  1. Cover one of the white ports, then blow air into the other white port and make sure air does not flow from the yellow port.
  2.  
  3. Install the check valve with the yellow port facing the body side.
  4.  



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Fig. Fig. 16: Make sure the check valve is installed correctly, yellow side facing the body

REMOVAL & INSTALLATION



When replacing any EVAP system hoses, always use hoses that are fuel-resistant or are marked EVAP. Use of hose which is not fuel-resistant will lead to premature hose failure.

Charcoal Canister

See Figure 17

Label and disconnect the lines running to the canister. On some models the air cleaner lid may need to be removed. Unbolt and extract the charcoal canister from the vehicle. Do not attempt to wash the charcoal canister. Also be sure that no activated carbon comes out of the canister during the cleaning process. Attach the charcoal canister to its mounting bracket and secure. Connect the vacuum hoses in their proper locations.



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Fig. Fig. 17: Exploded view of the charcoal canister and related components-5S-FE engine shown

Thermal Vacuum Valve (TVV)

See Figures 18 and 19

  1. Drain the coolant the from the radiator.
  2.  
  3. Disconnect and label the vacuum hoses from the charcoal canister and throttle body.
  4.  
  5. Remove the TVV valve from the engine.
  6.  

To install:
  1. Apply adhesive to 2 or 3 of the threads of the TVV, then tighten the valve to 22 ft. lbs. (29 Nm).
  2.  



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Fig. Fig. 18: Apply adhesive to 2 or 3 of the threads of the TVV prior to installation

On the 5S-FE engine, have the ports facing the direction shown in the illustration.



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Fig. Fig. 19: Insert the TVV and have the ports facing this angle when tightened

  1. Reattach the vacuum hoses.
  2.  
  3. Refill the engine with coolant. Start the engine, check and top off the fluid level.
  4.  

 
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