Chrysler Neon 1995-1999 Repair Guide

Evaporative Emission Controls

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OPERATION



The evaporation control system prevents the emission of fuel tank vapors into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to a charcoal filled evaporative canister. This canister holds the vapors temporarily. The Powertrain Control Module (PCM) allows intake manifold vacuum to draw vapors into the combustion chambers during certain operating conditions. The evaporation control system is made up of the following components:

Rollover Valve

All vehicles are equipped with a rollover valve. This valve is a safely feature which prevents fuel flow through the fuel tank vent valve hoses, should the vehicle roll over in an accident. All vehicles pass a 360° rollover.

EVAP Canister

See Figure 1

All vehicles used a sealed, maintenance free evaporative (EVAP) canister. Fuel tank pressure vents into the canister. The canister temporarily holds the fuel vapors until intake manifold vacuum draws them into the combustion chamber. The PCM purges the canister through the duty cycle EVAP purge solenoid. The canister is purged at intervals and engine conditions predetermined by the PCM.

The canister mounts to a bracket located behind the front passenger's side fascia. The vacuum and vapor tubes connect to the top of the canister.



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Fig. Fig. 1: The evaporative canister is mounted to a bracket found behind the front fascia on the passenger's side of the vehicle

Duty Cycle Evaporative Purge Solenoid Valve

See Figure 2

The duty cycle EVAP purge solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The PCM operates the solenoid. During the cold start warm up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged.

When purging, the PCM energizes and de-energizes the solenoid about 5-10 times per second, depending upon operation conditions. The PCM varies the vapor flow rate by changing the solenoid pulse width. Pulse width is the amount of time the solenoid energizes.



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Fig. Fig. 2: The duty cycle evaporative purge solenoid valve is located near the front engine mount

The solenoid is attached to a bracket that is secured to the front engine mount. The solenoid will not operate properly unless it is installed with the electrical connector at the top.

Pressure-Vacuum Filler Cap

See Figure 3

A pressure vacuum relief cap is used to seal the fuel tank. Tightening the cap on the fuel filler tube creates a seal between them. The relief valves in the cap are a safety feature which prevent possible excessive pressure or vacuum in the fuel tank. Excessive fuel tank pressure could be caused by a malfunction in the system to damage to the vent lines.



Click image to see an enlarged view

Fig. Fig. 3: If you ever have to replace the gas tank cap, make sure you get the proper one for your vehicle

When the cap is removed, the seal is broken and fuel tank pressure is relieved. If the filler cap ever needs to be replaced, make sure to get the correct part.

Leak Detection Pump

Some vehicles use a leak detection pump which is a device used to find leaks in the evaporative emission system. The pump has a 3-port solenoid, a pump that contains a switch, a spring loaded canister vent valve seal, 2 check valves and a spring/diaphragm.

COMPONENT TESTING



Evaporative System Check
  1. Before beginning the check, inspect all connectors for a clean, tight fit.
  2.  
  3. Start the engine and allow it to reach normal operating temperatures.
  4.  
  5. Inspect the throttle body-to-evaporative emission solenoid vacuum line. Check for vacuum leaks or restrictions. If the vacuum line is damaged, replace or repair as necessary. If the line is OK, proceed with the test.
  6.  
  7. Check the vacuum line running from the evaporative solenoid to the canister for damage or restriction. If the vacuum line is damaged, replace or repair as necessary. If the line is OK, proceed with the test.
  8.  
  9. Disconnect the canister-to-solenoid vacuum line from the solenoid. Is the evaporative solenoid allowing vacuum to cycle through intermittently at a steady rate- If not, replace the evaporative solenoid. If so, proceed with the test.
  10.  

During the next steps, do NOT use more than 5 psi of air pressure.

  1. Turn the ignition key to the OFF position. Attempt to blow air through the vacuum line that goes to the canister. Do the canister and vacuum line allow air to pass- If so, the purge solenoid and hoses are OK. If not, proceed with the test.
  2.  
  3. Disconnect the solenoid-to-canister vacuum line from the canister. Try to blow air through the vacuum line that goes to the canister. Does the line let air pass- If so, replace the evaporative canister. If not, repair or replace the vacuum line, as necessary.
  4.  

REMOVAL & INSTALLATION



Evaporative Canister
  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle. Remove the front passenger's side wheel and tire assembly.
  4.  
  5. Remove the retainers, then remove the splash shield.
  6.  
  7. Tag and disconnect the vacuum lines from the evaporative canister.
  8.  
  9. Push the locking tab on the electrical connector to unlock and remove the connector.
  10.  
  11. Unafsten the 3 retaining nuts, then remove the canister from the mounting bracket.
  12.  

To install:
  1. Install the evaporative canister to the bracket, then secure with the retaining nuts. Tighten to 50 inch lbs. (5.6 Nm).
  2.  
  3. Attach the electrical connector to the pump, then push the locking tab to lock the connector in place.
  4.  
  5. Connect the vacuum lines to the canister, as tagged during removal.
  6.  
  7. Install the splash shield, securing it with the retainers.
  8.  
  9. Install the wheel and tire assembly, then carefully lower the vehicle.
  10.  
  11. Connect the negative battery cable.
  12.  

Leak Detection Pump

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the evaporative canister from the vehicle.
  4.  
  5. Remove the pump and bracket, as an assembly.
  6.  
  7. Remove the pump from the bracket.
  8.  

To install:
  1. Install the pump and bracket assembly to the body, then tighten the retaining bolts to 20 inch lbs. (3 Nm).
  2.  
  3. Install the evaporative canister, as outlined earlier.
  4.  
  5. Connect the negative battery cable.
  6.  

 
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