Jeep Wagoneer/Commando/Cherokee 1984-1998

Evaporative Emission Control System

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OPERATION



The evaporative emission control system prevents the release of unburned hydrocarbons, from gasoline or gasoline vapor, into the atmosphere. When pressure in the fuel tank is below 3 psi (20 kPa), the pressure relief/rollover valves open allowing fuel vapors to flow to the evaporative canister where they are absorbed by a charcoal mixture. This prevents excessive pressure build-up in the fuel system. Most canisters are equipped with a calibrated orifice at the inlet to the canister.

The evaporative canister is mounted to the passenger side frame rail. Inlet ports on the canister are connected to the rollover/pressure relief valves, the air cleaner, and the fuel tank vent through hoses and tubes.

Canister purge operation is activated by the purge shutoff switch. An air cleaner venturi provides the vacuum to open the switch which allows vapors collected in the canister to be drawn into the airstream. The vapors then pass through the intake manifold and are burned in the combustion process.

The fuel tanks of all vehicles are equipped with two pressure relief/rollover valves. The valves relieve fuel tank pressure and prevent fuel flow through the fuel tank vent hoses in the event of vehicle rollover.

The valves consist of a plunger, spring, orifice and guide plate. The valve is normally open allowing fuel vapor to vent to the canister. If the bottom of the plunger is contacted by sloshing fuel, the plunger seats in the guide plate preventing fuel from reaching the canister.

If the vehicle should roll over, the valve is inverted and the plunger is forced against the guideplate, preventing fuel from flowing through the vent tube.

Removal & Installation



Evaporative Canister
EXCEPT 1996-98 GRAND CHEROKEE and 1998 CHEROKEE

See Figure 1

  1. Tag and disconnect the vacuum lines from the canister.
  2.  
  3. Remove the canister strap bolt and remove the canister from the vehicle.
  4.  
  5. Installation is the reverse of removal. Tighten the bolt to 45 inch. lbs. (5 Nm).
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the EVAP cannister and related components-1996 Cherokee model shown

1996-98 GRAND CHEROKEE

See Figures 2 and 3



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Fig. Fig. 2: Exploded view of the cannister location for the 4.0L California emission package-1996 Grand Cherokee model

  1. Remove the grille and the front bumper/fascia assembly as outlined in General Information & Maintenance 0.
  2.  
  3. Tag and disconnect the vacuum lines from the canister.
  4.  
  5. Unfasten the canister retaining nuts and remove the canister through the bottom of the vehicle.
  6.  

To install:
  1. Install the canister and tighten the retaining nuts to 80 inch. lbs. (9 Nm).
  2.  
  3. Connect the vacuum lines.
  4.  
  5. Install the front bumper/fascia assembly and the grille as outlined in General Information & Maintenance 0.
  6.  



Click image to see an enlarged view

Fig. Fig. 3: Exploded view of the cannister location except the California emission package-1996 Grand Cherokee model

1998 CHEROKEE

The EVAP canister is located below the left side of the vehicle near the front of the rear axle.

  1. Tag and disconnect the vacuum lines from the canister.
  2.  
  3. Unfasten the canister mounting bracket retaining nuts and remove the canister/bracket assembly from the vehicle.
  4.  
  5. Installation is the reverse of the removal procedures.
  6.  

Purge Solenoid

See Figure 4

  1. Disengage the solenoid electrical connection.
  2.  
  3. Tag and disconnect the solenoid vacuum lines.
  4.  
  5. Unfasten the solenoid retaining nuts and remove the solenoid.
  6.  
  7. Installation is the reverse of removal. Tighten the retaining fasteners to 45 inch. lbs. (5 Nm).
  8.  



Click image to see an enlarged view

Fig. Fig. 4: Common EVAP canister purge solenoid and related components

Pressure Relief/Rollover Valve

See Figures 5 and 6



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Fig. Fig. 5: Cutaway view of the pressure relief/rollover valve

  1. Disconnect the battery negative cable.
  2.  
  3. Relieve the fuel system as outlined in Fuel System .
  4.  

DO NOT allow fuel to spill on the intake or exhaust manifolds. Use shop rags to absorb any spilled fuel.

  1. Drain the fuel tank dry using a siphon pump.
  2.  
  3. Raise and support the vehicle with jackstands.
  4.  
  5. Remove the fuel tank. See appropriate procedure in Fuel System .
  6.  
  7. If equipped, remove the vapor hose at the valve.
  8.  
  9. The rollover valve is seated in a grommet. Pry one side of the valve up and twist to remove the grommet from the tank.
  10.  

To install:
  1. Start one side of the grommet into the fuel tank opening and using finger pressure only, press the valve grommet into position.
  2.  
  3. Engage the vapor hose, if equipped.
  4.  
  5. Install the tank as outlined in Fuel System .
  6.  
  7. Fill the tank and connect the negative battery cable.
  8.  
  9. Start the vehicle and check for leaks.
  10.  



Click image to see an enlarged view

Fig. Fig. 6: View of the pressure relief/rollover valve location

Pressure-Vacuum Fuel Tank Filler Cap

The fuel filler cap is equipped with a two-way relief valve that is closed during normal operation of the vehicle. The relief valve is calibrated to open only when conditions equal or exceed 1.5 psi of pressure or 1.8 in.Hg of vacuum. When the vacuum or pressure is relieved, the valve returns to the closed position.

 
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