Ram B1500, B2500, B3500, 1999-2003

Evaporative Emission Control System

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Gasoline fuel is a major source of pollution, before and after it is burned in the automobile engine. From the time the fuel is refined, stored, pumped and transported, again stored until it is pumped into the fuel tank of the vehicle, the gasoline gives off unburned hydrocarbons (HC) into the atmosphere. Through the redesign of storage areas and venting systems, the pollution factor was diminished, but not eliminated, from the refinery standpoint. However, the automobile still remained the primary source of vaporized, unburned hydrocarbon (HC) emissions.

Fuel pumped from an underground storage tank is cool but when exposed to a warmer ambient temperature, will expand. Before controls were mandated, an owner might fill the fuel tank with fuel from an underground storage tank and park the vehicle for some time in warm area, such as a parking lot. As the fuel would warm, it would expand and should no provisions or area be provided for the expansion, the fuel would spill out of the filler neck and onto the ground, causing hydrocarbon (HC) pollution and creating a severe fire hazard. To correct this condition, the vehicle manufacturers added overflow plumbing and/or gasoline tanks with built in expansion areas or domes.

However, this did not control the fuel vapor emission from the fuel tank. It was determined that most of the fuel evaporation occurred when the vehicle was stationary and the engine not operating. Most vehicles carry 5-25 gallons (19-95 liters) of gasoline. Should a large concentration of vehicles be parked in one area, such as a large parking lot, excessive fuel vapor emissions would take place, increasing as the temperature increases.

To prevent the vapor emission from escaping into the atmosphere, the fuel systems were designed to trap the vapors while the vehicle is stationary, by sealing the system from the atmosphere. A storage system is used to collect and hold the fuel vapors from the carburetor (if equipped) and the fuel tank when the engine is not operating. When the engine is started, the storage system is then purged of the fuel vapors, which are drawn into the engine and burned with the air/fuel mixture.

Evaporative Canister



Gasoline-engined vehicles are fitted with an EVAP control system.

The EVAP control system prevents gasoline vapors from escaping into the atmosphere. When fuel evaporates from the fuel tank, the vapors pass through vent hoses or tubes to the carbon-filled EVAP canister. They are temporarily held in the canister until they can be drawn into the intake manifold when the engine is running.

Location and configuration of EVAP canister varies with model, year and engine. Most are mounted on a frame rail (left or right) forward of the fuel tank. The Ram 1500-3500 trucks utilize two EVAP canisters, located side-by-side on the outside of the left frame rail, in front of the fuel tank.



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Fig. Typical EVAP canister mounting-Dakota/Durango shown



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Fig. Typical EVAP canister mounting-Ram 1500-3500



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Fig. EVAP canister mounted on the left frame rail-1997 Ram 1500

The canister is purged by the EVAP canister purge solenoid at predetermined times and certain engine operating conditions.

The EVAP canister purge solenoid controls the vacuum that draws the vapors from the canister. The Powertrain Control Module (PCM) controls the solenoid. The PCM operates the solenoid by either switching the ground circuit on or off. When energized the solenoid prevents vacuum from reaching the EVAP canister. When not energized, the solenoid allows vacuum to flow to the EVAP canister. The purge solenoid is mounted to a bracket located near the left-rear side of the intake manifold.

The solenoid opens when the engine reaches normal operating temperature and the vehicle is moving.

Operation



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 that 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 vent hoses or tubes to a charcoal-filled evaporative canister. When the engine is operating the vapors are drawn into the intake manifold.

The PCM determines when these vapors will be passed into the intake manifold.

Evaporative Emissions Canister

A sealed, maintenance-free evaporative canister is used (some RAM trucks have two). The canister is mounted under the vehicle on the frame rail behind the cab. It may be on either side (or both sides) of the vehicle depending on model and year.

The canister is filled with granules of an activated carbon mixture, which absorb fuel vapors.

Fuel Tank Cap

The fuel tank is sealed with a pressure-vacuum relief filler cap. Under normal operating conditions, the filler cap operates as a check valve, allowing air to enter the tank to enable fuel flow. At the same time, it prevents fuel vapors from escaping through the cap to the atmosphere. These vapors are therefore forced into the EVAP canister.

The relief valves in the cap are 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.

Leak Detection Pump

Certain emissions packages have a Leak Detection Pump (LDP) is used to monitor the EVAP system for leaks. On most models so equipped, this unit is located beneath the battery tray. A test port for pressurizing the EVAP system is included. The test port is used to pressurize the system with a special gas and serious precautions must be taken to avoid damage to the EVAP system and the fuel tank. This is a procedure best suited to a professional shop, due to the precautions and the equipment needed to test this system. The PCM can store trouble codes for EVAP system performance.

Purge Solenoid

All gasoline engines use a duty cycle purge system. The PCM controls vapor flow by operating the duty cycle EVAP purge solenoid. This regulates the rate of vapor flow from the EVAP canister to the intake manifold.

The PCM 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.

During warm up and for a specified time after hot starts, the PCM energizes (grounds) the solenoid 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 solenoid, allowing vacuum to flow through the canister and purges vapors through the throttle body. During certain idle conditions, the purge solenoid may be grounded to control fuel mix calibrations.

After the engine reaches operating temperature, the PCM energizes and de-energizes the solenoid 5-10 times per second, depending on operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width, which is the amount of time the solenoid energizes.

Rollover Valves

Two-door models have one rollover valve located on top of the fuel tank. Four-door models have two valves also located on top of the fuel tank, although configuration may differ by model. Some vehicles have valves mounted at front and rear of the tank, while others may have one of the valves located atop the fuel pump.

Rollover valves prevent fuel flow through the EVAP hoses in the event of an accidental vehicle rollover. The EVAP canister(s) draw vapor from the gas tank through the valve(s).

Tank-mounted rollover valves are not serviceable and can only be replaced with the tank. Pump-mounted valves can be serviced separately.



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Fig. EVAP system incorporating leak detection pump



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Fig. Typical EVAP canister mounting-Dakota, Durango shown



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Fig. EVAP canister mounted on a 97 RAM truck



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Fig. Another EVAP mounting configuration-99 RAM truck



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Fig. Purge solenoid and LDP installation-RAM truck shown



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Fig. Tank-mounted rollover valves



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Fig. Fuel pump-mounted rollover valve



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Fig. A typical fuel tank filler tube cap

Removal & Installation




NOTE
To relieve fuel tank pressure, the filler cap must be removed before disconnecting any fuel system component.

Canister Purge Solenoid Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the electrical wiring from the solenoid.
  4.  
  5. Disconnect the vacuum lines from the solenoid.
  6.  
  7. Remove the solenoid or solenoid with support bracket as an assembly if this is easier.
  8.  

To install:

  1. Install the solenoid or support bracket.
  2.  
  3. Connect the vacuum lines.
  4.  
  5. Connect the wiring harness.
  6.  
  7. Connect the negative battery cable.
  8.  

Evaporative Emission Canister
  1. Disconnect the negative battery cable.
  2.  
  3. Raise and support the vehicle.
  4.  
  5. Label and disconnect the hoses on the top of the canister.
  6.  
  7. Remove the mounting bolts or nut(s).
  8.  

To install:

  1. Install and tighten the mounting hardware to 7 ft. lbs. (9 Nm), if two nuts or bolts are used. Tighten to 18 ft. lbs. (24 Nm), for single fasteners.
  2.  
  3. Install the hoses in their proper locations.
  4.  
  5. Lower the vehicle.
  6.  
  7. Connect the negative battery cable.
  8.  



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Fig. Mark the lines connected to the EVAP canister before removal to ease installation

Leak Detection Pump
  1. The Leak Detection Pump (LDP) and filter are attached to a bracket mounted to the right side inner fender. LDP and filter are serviced as a single assembly.
  2.  
  3. Remove the LDP filter hose.
  4.  
  5. Remove the filter mounting bolt and remove the filter from the vehicle.
  6.  
  7. Disconnect the vacuum lines at the LDP.
  8.  
  9. Disconnect the LDP wiring.
  10.  
  11. Remove the mounting screws and remove the LDP from the vehicle.
  12.  

To install:

  1. Reverse the removal procedure. Be sure all connections are TIGHT.
  2.  

Rollover Valve
  1. Tank-mounted rollover valves are molded into the gas tank and are not replaceable. The following procedure refers to pump-mounted valves only.
  2.  
  3. Disconnect the battery negative cable(s).
  4.  
  5. Drain the fuel tank.
  6.  
  7. Remove the fuel tank from the truck.
  8.  
  9. Disconnect the line at the rollover valve.
  10.  
  11. The valve is kept by a rubber grommet. Pry one side upward and roll it out.
  12.  

To install:

  1. Use a new grommet.
  2.  
  3. Press the valve in using finger pressure only.
  4.  

Testing




NOTE
To relieve fuel tank pressure, the filler cap must be removed before disconnecting any fuel system component.

Canister Purge Solenoid Valve
  1. Locations vary depending on model and year. Typical locations include the firewall (left or right side) and the rear of the engine near the firewall.
  2.  
  3. With the ignition off, unplug the connector on the EVAP solenoid.
  4.  
  5. Turn ignition on, measure the voltage at the ignition switch output line, voltage should be 10.0v or more. If the voltage reading is not 10.0 volts or more, repair the circuit from the ignition switch to EVAP solenoid.
  6.  
  7. Disconnect the negative battery cable.
  8.  
  9. Disconnect the PCM harness from the PCM.
  10.  
  11. Check the resistance of the EVAP solenoid control circuit between the PCM harness connector and the EVAP solenoid connector. Resistance should be less than 5.0 ohms; if not, repair the opening in the circuit.
  12.  
  13. Connect the negative battery cable.
  14.  



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Fig. Purge solenoid mounted on V-8 engine



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Fig. Purge solenoid installation on 2.5L engine-equipped vehicles



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Fig. EVAP solenoid circuits and schematic



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Fig. EVAP solenoid electrical connector

Servicing

NOTE
The hoses used in this system are specifically manufactured for this application. If replacement becomes necessary, it is important to use only fuel resistant hose.

The EVAP canister is sealed and maintenance-free. However, a periodic inspection of the unit and vent hoses is advisable. Although the factory does not give recommendations here, you should inspect the unit at least every six months or 6000 miles (9600 km). During your inspection, make sure the unit is mounted firmly in its bracket, that it is not cracked and that the vent hoses are connected and not cracked. Correct any problems you may discover, or refer to the removal and installation procedure under "DRIVEABILITY AND EMISSION CONTROLS" if you suspect the unit itself is malfunctioning.

 
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