Acura Coupes and Sedans 1994-2000 Repair Information

Evaporative Emission Controls

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OPERATION



See Figure 1

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Fig. Fig. 1: Evaporative emissions component schematic

Changes in atmospheric temperature cause fuel tanks to breathe, that is, the air within the tank expands and contracts with outside temperature changes. If an unsealed system was used, when the temperature rises, air would escape through the tank vent tube or the vent in the tank cap. The air which escapes contains gasoline vapors.

The Evaporative Emission Control System provides a sealed fuel system with the capability to store and condense fuel vapors. When the fuel evaporates in the fuel tank, the vapor passes through the EVAP emission valve, through vent hoses or tubes to a carbon filled evaporative canister. When the engine is operating the vapors are drawn into the intake manifold and burned during combustion..

A sealed, maintenance free evaporative canister is used. The canister is filled with granules of an activated carbon mixture. Fuel vapors entering the canister are absorbed by the charcoal granules. A vent cap is located on the top of the canister to provide fresh air to the canister when it is being purged. The vent cap opens to provide fresh air into the canister, which circulates through the charcoal, releasing trapped vapors and carrying them to the engine to be burned.

Fuel tank pressure vents fuel vapors into the canister. They are held in the canister until they can be drawn into the intake manifold. The canister purge valve allows the canister to be purged at a pre-determined time and engine operating conditions.

Vacuum to the canister is controlled by the canister purge valve. The valve is operated by the PCM. The PCM regulates the valve by switching the ground circuit on and off based on engine operating conditions. When energized, the valve prevents vacuum from reaching the canister. When not energized the valve allows vacuum to purge the vapors from the canister.

During warm up and for a specified time after hot starts, the PCM energizes (grounds) the valve preventing vacuum from reaching the canister. When the engine temperature reaches the operating level of about 120°F (49°C), the PCM removes the ground from the valve allowing vacuum to flow through the canister and purges vapors through the throttle body. During certain idle conditions, the purge valve may be grounded to control fuel mixture calibrations.

The fuel tank is sealed with a pressure-vacuum relief filler cap. The relief valve in the cap is a safety feature, preventing excessive pressure or vacuum in the fuel tank. If the cap is malfunctioning, and needs to be replaced, ensure that the replacement is the identical cap to ensure correct system operation.

COMPONENT TESTING Evaporative Emissions (EVAP) Control Canister



This canister is used as a storage facility for fuel vapors which have escaped from components such as the fuel tank. This canister prevents these vapors from entering into the atmosphere.

Generally, the only testing done to the canister is a visual inspection. Look the canister over and replace it with a new one if there is any evidence of cracks or other damage.

Evaporative Hoses and Tubes

Inspect all system hoses and tubes for signs of damage or cracks. Any damage or leakage must be repaired.

Evaporative Emissions Control Shunt Valve/Solenoid Valve. See Figure 2

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Fig. Fig. 2: Typical emissions control shunt valve

The Integra's control valve is located on the top of the intake manifold. On 2.5L engines, the valve is located on the right front side of the engine compartment.

See Figure 5

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Fig. Fig. 3: Location of EVAP shunt valve

The evaporative emissions control shunt valve is located at the top of the charcoal canister.

  1. Disconnect the vacuum hose from the valve.
  2.  
  3. Remove the canister vent shunt valve from the canister.
  4.  
  5. Turn the ignition switch ON .
  6.  
  7. Apply vacuum to the hose.
  8.  
  9. If it holds vacuum, check for a short in the wire.
  10.  
  11. When finished testing, attach all disconnected hoses, connectors, and wires.
  12.  

REMOVAL & INSTALLATION Evaporative Emissions Canister



See Figure 4

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Fig. Fig. 4: EVAP three-way valve and control canister

  1. Raise and support the vehicle.
  2.  
  3. Remove the bolts retaining the Evaporative Emissions (EVAP) canister and bracket assembly.
  4.  
  5. Label and disconnect the vapor hoses from the canister.
  6.  
  7. Remove the canister from the bracket.
  8.  
  9. Installation is the reverse of the removal procedure.
  10.  

Evaporative Emissions Control Shunt Valve See Figure 5 EVAP 3 way valve and control canister.

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Fig. Fig. 5: Evap Control Canister

  1. Disconnect the vacuum hose from the EVAP shunt valve.
  2.  
  3. Remove the fasteners which hold the EVAP shunt valve to the canister.
  4.  
  5. Remove the EVAP control shunt valve from the canister.
  6.  

To install:
  1. Install the EVAP control shunt valve and fasteners.
  2.  
  3. Connect all vacuum hoses.
  4.  

Canister Purge Valve (Two-Way Valve) See Figure 6

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Fig. Fig. 6: Typical EVAP two-way valve

  1. Raise and support the vehicle.
  2.  
  3. Disconnect the electrical harness from the valve.
  4.  
  5. Disconnect the fuel vapor hoses and remove the valve.
  6.  
  7. Installation is the reverse of the removal procedure.
  8.  

 
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