Chrysler Full-Size Trucks 1989-1996 Repair Guide

Evaporative Emission Controls

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OPERATION



See Figures 1, 2, 3 and 4

Changes in atmospheric temperature cause fuel tanks to breathe; that is, the air within the tank expands and contracts with outside temperature changes. As the temperature rises, air escapes through the tank vent tube or the vent in the tank cap. Unless contained, the air which escapes will contain gasoline vapors.



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Fig. Fig. 1: A common mounting point of the evaporative emission control canister-1434-43 Ram and Ramcharger

The Evaporative Emission Control System (also called the EVAP system on later models) provides a sealed fuel system with the capability to store and condense gasoline vapors (diesel vehicles are not equipped with this system). The system has three parts: a fill control vent system; a vapor vent and storage system; and a pressure and vacuum relief system (special fill cap).

When fuel evaporates from the fuel tank, the vapors are vented to a carbon-filled evaporative (EVAP) canister where they are temporarily held until they can be drawn into the intake manifold.

The vapors are drawn into the engine at idle and off idle. This system employs a dual source of vacuum and is called a Bi-Level Purge System. The vacuum is controlled by the EVAP canister purge solenoid.



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Fig. Fig. 2: An evaporative emission control canister as found on the Dakota

The purge solenoid is controlled by the engine controller computer. The computer regulates the solenoid by switching the ground circuit on and off based on engine operating conditions. When energized, the solenoid prevents vacuum from reaching the canister. When not energized, the solenoid allows vacuum to flow through to the canister.



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Fig. Fig. 3: The evaporative canister purge solenoid is located with other emissions control solenoids and shares a common mount near the right cylinder head-V1 and V3 engines



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Fig. Fig. 4: Location of the evaporative canister purge solenoid-Dakota

All vehicles are equipped with a combination pressure relief and roll-over valve. The valve provides a path for fuel vapors to travel from the fuel tank to the canister and also provides fuel leakage protection should the vehicle become inverted through accident or carelessness. This valve incorporates a pressure relief mechanism which is designed to release pressure to the atmosphere when the fuel tank pressure increases beyond the calibrated setting.

These vehicles also use a sealed filler cap that has a pressure-vacuum relief valve. Under normal operating conditions, the filler cap operates as a check valve, allowing air to enter the tank to replace the fuel consumed. At the same time, it prevents vapors from escaping through the cap. In case of excessive pressure within the tank, the filler cap valve opens to relieve the pressure.

Because the filler cap is sealed, fuel vapors have only one place through which they may escape: the vapor separator assembly at the top of the fuel tank and into the evaporative (EVAP) canister.

REMOVAL & INSTALLATION



Evaporative (EVAP) Canister

See Figures 1, 2, 3 and 4

The evaporative canister is located on the right side wheel well on 1434-43 Ram and Ramcharger vehicles, and the left frame rail, near the left door for 1444-41 Ram vehicles. For Dakota models, it is found on the right side radiator closure panel (earlier models), or the right side inner fender (later models).

  1. If necessary, raise and safely support the vehicle.
  2.  
  3. Detach the fuel lines/tubes at the canister. Make note of the location of these fittings prior to removal to allow proper installation.
  4.  
  5. Remove the mounting bolt at the canister mounting strap.
  6.  
  7. Remove the canister from the bracket.
  8.  

To install:
  1. Position the canister in the mounting bracket.
  2.  
  3. Rotate the canister until the fittings are pointed in the up position.
  4.  
  5. Install the mounting bolt and tighten it to 45 inch lbs. (10 Nm).
  6.  
  7. If raised, carefully lower the vehicle.
  8.  
  9. Install the tubes/lines.
  10.  

Evaporative (EVAP) Canister Purge Solenoid

See Figure 5

  1. Remove the air cleaner housing assembly.
  2.  
  3. Disengage the wiring connector and vacuum harness from the solenoid.
  4.  
  5. Remove the solenoid and its support bracket from the intake manifold.
  6.  



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Fig. Fig. 5: The EVAP canister purge solenoid (arrow) is mounted above the exhaust manifold

  1. Remove the solenoid from the mounting bracket (on the 3.0L engine, it will snap off).
  2.  

To install:
  1. Install the solenoid to the bracket and install the bracket to the intake manifold (for the 3.0L engine, the solenoid will snap in place).
  2.  
  3. Connect the vacuum harness and wiring.
  4.  
  5. Install the air cleaner housing.
  6.  

 
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