Hyundai Coupes/Sedans 1994-1998 Repair Guide

Evaporative Emission Controls

Print

OPERATION



See Figures 1 and 2



Click image to see an enlarged view

Fig. Fig. 1: Diagram of an early model evaporative emission control system



Click image to see an enlarged view

Fig. Fig. 2: Diagram of a late model evaporative emission control system with FTP sensor

The evaporative emission control system prevents the uncontrolled release of gasoline vapors (hydrocarbons) into the atmosphere. These vapors are produced when fuel evaporates in the sealed fuel tank. The system includes a charcoal canister, canister purge solenoid valve, fuel check valve, overfill limiter, fuel cap and on some late model vehicles, a fuel tank pressure (FTP) sensor and a canister close valve (CCV).

The main component of the system is the charcoal canister. The activated charcoal in the canister absorbs and stores fuel vapors generated inside the fuel tank while the engine is inoperative. When the engine is running, the vapors are drawn through the electronically controlled purge control valve and into the intake manifold. The vapors enter the air/fuel mixture and are burned in the combustion process.

The overfill limiter (two way valve) consists of a pressure valve and a vacuum valve. The pressure valve is designed to open when the fuel tank's internal pressure has increased over the preset pressure limit. The vacuum valve opens when a vacuum is produced in the tank.

The fuel check valve is used to prevent fuel leakage should the vehicle roll over. The valve is connected in the fuel vapor line between canister and overfill limiter. The fuel check valve contains 2 balls and under normal conditions the gasoline vapor passage in the valve is open; if a vehicle roll over occurs, one of the balls closes the fuel passage thus preventing fuel leaks.

A special fuel cap is installed on these vehicles which prevents vapors from escaping through the filler neck.

An FTP sensor and a CCV are used on 2.0L (VIN F) and 1996-98 1.8L (VIN M) engines. The sensor monitors differential pressure between the inside and outside of fuel tank. It signals the electronic control module (ECM) which controls the canister close valve.

The evaporative emission system should be inspected every 52,000 miles (84,000 km).

TESTING



Evaporative Emission System
  1. Disconnect the vacuum hose (red stripe) from the throttle body and connect a hand held vacuum pump. Plug the nipple on the throttle body.
  2.  
  3. Check if vacuum is held or released as specified in accompanying chart.
  4.  
  5. Replace vacuum lines or components as necessary after performing component inspection.
  6.  

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: Evaporative Emission Diagnostic Chart

Charcoal Canister

See Figure 4



Click image to see an enlarged view

Fig. Fig. 4: The charcoal canister absorbs and stores fuel vapors generated inside the fuel tank while the engine is inoperative releases them into the running engine to be burned in the combustion process

TWO PORT (ROUND) CANISTER

There is no practial way to test the two port canister. It is suggested that the canister and lines be inspected for obvious damages as follows:

  1. Inspect the canister for loose connections, sharp hose bends or damage to the fuel vapor lines.
  2.  
  3. Look for distortion, cracks or fuel leakage.
  4.  
  5. Remove the canister and inspect case for cracks or damage.
  6.  
  7. Replace canister as required.
  8.  

THREE PORT (SQUARE) CANISTER

See Figure 5



Click image to see an enlarged view

Fig. Fig. 5: Three port canister hose identification

  1. Inspect the canister for loose connections, sharp hose bends or damage to the fuel vapor lines.
  2.  
  3. Look for distortion, cracks or fuel leakage.
  4.  
  5. Remove the canister and inspect case for cracks or damage.
  6.  
  7. Blow low pressure air into the fuel tank side hose and check that air flows without obstructions.
  8.  
  9. Blow low pressure air into the EVAP canister purge solenoid valve side hose and check at air flows without obstructions.
  10.  
  11. Place a finger over the EVAP canister purge solenoid valve side hose and blow low pressure air into the fuel tank side hose. Inspect for leaks.
  12.  
  13. Replace the canister if it does not function as specified.
  14.  

Canister Purge Solenoid Valve

See Figure 6



Click image to see an enlarged view

Fig. Fig. 6: The purge solenoid valve is first tested as part of the system, then tested individually

  1. Disconnect the vacuum hose (red and black striped) from the purge solenoid valve.
  2.  
  3. Disconnect the electrical terminal harness connector from the valve.
  4.  
  5. Connect the vacuum pump to the nipple on the valve from which the red and black striped hose was disconnected.
  6.  
  7. Connect the 12 volt power source to the valve terminals.
  8.  
  9. Apply vacuum to the valve with the vacuum pump and alternately apply and remove battery voltage at the valve terminals. When battery voltage is applied, vacuum should be released from the valve. When voltage is removed, the valve should hold a steady vacuum.
  10.  
  11. Remove the vacuum pump and voltage source. Connect an ohmmeter to the valve terminals to measure the coil resistance. The resistance should be as follows:

    45 ohms at 68°F (20°C)-Scoupe
     
    26 ohms at 68°F (20°C)-Accent, Tiburon and 1996-98 Elantra
     
    36-44 ohms at 68°F (20°C)-Excel, Sonata and 1994-95 Elantra
     

  12.  
  13. If the valve does not operate as described or if the solenoid coil resistance is not as specified, replace the valve.
  14.  

Overfill Limiter (Two Way Valve)

See Figure 7



Click image to see an enlarged view

Fig. Fig. 7: The overfill limiter valve controls the pressure inside the fuel tank. It contains both a pressure valve and a vacuum valve

  1. Lightly breathe into the inlet and outlet.
  2.  
  3. If the air passes through after slight resistance, the valve is functioning properly.
  4.  

Fuel Filler Cap

See Figure 8



Click image to see an enlarged view

Fig. Fig. 8: The fuel cap is an important part of the evaporative emission system. It works in conjunction with the overfill limiter valve to control pressure inside the fuel tank

  1. Check the cap gasket and the cap for damage or deformation.
  2.  
  3. Replace the fuel cap as necessary.
  4.  

Fuel Tank Pressure (FTP) Sensor

See Figure 9



Click image to see an enlarged view

Fig. Fig. 9: The FTP is located at the filler neck. A voltage test with the engine running will determine if the sensor is functional

  1. Disconnect the FTP electrical harness.
  2.  
  3. Connect a voltmeter to FTP terminals 2 and 3.
  4.  
  5. Start the engine and allow it to idle for 20 minutes.
  6.  
  7. Voltmeter should read 5 volts at idle and drop to 0.5-4.5 volts when the engine is accelerated.
  8.  
  9. If voltage is not as specified, there is a leak in the system.
  10.  

Canister Close Valve (CCV)

See Figure 10



Click image to see an enlarged view

Fig. Fig. 10: The CCV is located on the evaporative canister. A piece of paper can be used to check valve operation when power is applied and removed from the connector

  1. Disconnect the CCV electrical harness.
  2.  
  3. Connect the CCV to a power source as illustrated.
  4.  
  5. Start the engine and allow it to idle.
  6.  
  7. Disconnect the CCV connector.
  8.  
  9. Ensure the CCV is closed when providing ground and open when ground is removed.
  10.  
  11. The best way to determine if the CCV is open or closed, is to place a thin piece of paper over the hose. If the paper is drawn to the hose or pushed away, the CCV is open.
  12.  

REMOVAL & INSTALLATION



Charcoal Canister

The canister is located either in the engine compartment at either the left or right front, near the headlights.

  1. Remove any components necessary to gain access to the canister.
  2.  
  3. Label and disconnect the vacuum lines.
  4.  
  5. Label and disconnect the electrical harness.
  6.  
  7. On round canisters, loosen the canister retaining strap.
  8.  
  9. On square canisters, remove the canister mounting hardware.
  10.  
  11. Remove the canister.
  12.  

To Install:
Canister Purge Solenoid Valve
  1. Install the canister.
  2.  
  3. On square canisters, install the canister mounting hardware and tighten securely.
  4.  
  5. On round canisters, tighten the canister retaining strap.
  6.  
  7. Connect the electrical harness.
  8.  
  9. Connect the vacuum lines.
  10.  
  11. Install any components previously removed to gain access to the canister.
  12.  

Overfill Limiter

The overfill limiter is located in the vapor line either at the fuel tank or at the charcoal canister. Valves located at the fuel tank may require fuel tank removal to gain access to the valve.

  1. Remove the fuel tank, as required.
  2.  
  3. Loosen the hose clamps.
  4.  
  5. Disconnect the valve from the vapor line.
  6.  

To Install:
  1. Connect the valve to the vapor line.
  2.  
  3. Tighten the hose clamps.
  4.  
  5. Install the fuel tank, as required.
  6.  

Fuel Cap

The fuel cap screws on to the end of the fuel filler pipe. It has a special ratcheting action when tightening to prevent the cap from being overtightented. When removing the fuel cap, caution should be taken to loosen it slowly. This will allow any pressure build-up in the fuel tank to be released.

Fuel Tank Pressure (FTP) Sensor

The FTP is located at the filler neck.

  1. Remove interior panels necessary to gain access to the back of the fuel filler neck.
  2.  
  3. Label and disconnect the vapor hose.
  4.  
  5. Remove the FTP mounting hardware.
  6.  
  7. Remove the FTP.
  8.  

To Install:
  1. Install the FTP and tighten the mounting hardware securely.
  2.  
  3. Connect the vapor hose.
  4.  
  5. Install interior panels previously removed to gain access to the back of the fuel filler neck.
  6.  

Canister Close Valve (CCV)

The CCV is located at the charcoal canister.

  1. Label and disconnect the vapor hose.
  2.  
  3. Remove the CCV mounting hardware.
  4.  
  5. Remove the CCV.
  6.  

To Install:
  1. Install the CCV and tighten the mounting hardware securely.
  2.  
  3. Connect the vapor hose.
  4.  

 
label.common.footer.alt.autozoneLogo