Chrysler Front Wheel Drive Cars 4-CYL 1981-1995 Repair Information

Evaporation Control System



See Figures 1, 2 and 3

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Fig. Fig. 1: The fuel vapors drawn out of the fuel tank are stored in a vapor (charcoal) canister

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Fig. Fig. 2: The canister purge solenoid keeps vacuum from reaching the vacuum canister during and shortly after the engine start-up period

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Fig. Fig. 3: A schematic of the Evaporation (EVAP) control system used on 2.5L Premier engines

The evaporation control system prevents the emission of fuel tank vapors into the atmosphere. When fuel in the tank evaporates, the vapors pass through vent hoses or tubes to a charcoal canister. The canister temporarily holds the vapors. The Powertrain Control Module (PCM) allows intake manifold vacuum to draw vapors into the combustion chambers during certain operating conditions. The PCM uses the canister purge solenoid to regulate vapor flow.

On all 2.2L and 2.5L Chrysler EFI engines, the manifold vacuum purges the vapors at idle as well as off idle. These engines use a bi-level purge system. The system uses 2 sources of vacuum to remove fuel vapors from the canister.

The 2.2L Turbo III and 2.5L Turbo I engines utilize a tri-level canister purge system. In this system, fuel vapors are drawn into the engine through the throttle body and air cleaner. Fuel vapors are drawn in at closed throttle, part throttle, and Wide Open Throttle (WOT) in boost.

The evaporative system uses specially manufactured hoses. If they need replacement, only use fuel resistant hose.

All vehicles are equipped with a Vehicle Emission Control Information (VECI) label which is located in the engine compartment. The label contains emission specifications and vacuum hose routing. All hoses must be connected and routed as shown on the label.

Pressure Relief/Rollover Valve

See Figures 4 and 5

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Fig. Fig. 4: Cross-section view of the rollover valve used in Premier models

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Fig. Fig. 5: On Premier models, the rollover valve is mounted in the top of the fuel tank and held in place with a grommet

All vehicles have a combination pressure relief and rollover valve (Premier vehicles have two). The dual function valve relieves fuel tank pressure and also prevents fuel flow through the fuel tank vent valve hoses if the vehicle accidentally rolls over. All vehicles pass a 360° rollover test.

The pressure relief valve opens at a certain pressure. When the fuel tank pressure increases above the calibrated pressure, the valve opens to release fuel tank vapor pressure. The evaporative (charcoal) canister stores the vapors.

Evaporative Canister

See Figure 1

All vehicles use a sealed, maintenance free evaporative (charcoal) canister. The canister mounts to the inner wheel well area of the engine compartment.

Fuel tank pressure vents into the canister. The canister temporarily holds the fuel vapors until the intake manifold vacuum draws them into the combustion chamber. The canister purge solenoid purges vapors from the canister at predetermined intervals and engine conditions.

Canister Purge Solenoid

See Figure 2

The 2.2L and 2.5L Chrysler EFI, 2.5L Turbo I and 2.2L Turbo III engine-equipped vehicles are equipped with a canister purge solenoid. The engine PCM operates the canister purge solenoid. During warm-up and for a specified period after hot starts, the PCM grounds the purge solenoid causing it to energize. When the PCM grounds the solenoid, vacuum does not reach the charcoal canister valve.

When the engine reaches a specified operating temperature and the time delay interval has occurred, the PCM de-energizes the solenoid, vacuum flows to the canister purge valve. Intake manifold vacuum purges fuel vapors through the throttle body. The PCM also energizes the purge solenoid during certain idle conditions to update the fuel delivery calibration.

Duty Cycle Evaporation (EVAP) Purge Solenoid

The 2.5L Chrysler Flex Fuel engines use a duty cycle purge system. The PCM controls vapor flow by operating the duty cycle EVAP purge solenoid. The duty cycle EVAP purge solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body.

During the cold start warm-up period and the hot start time delay, the engine computer does not energize the solenoid. When de-energized, no vapors are purged. The engine computer de-energizes the solenoid during open loop operation.

The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During closed loop operation, the engine computer energizes and de-energizes the solenoid approximately 5-10 times per second, depending upon operating conditions. The engine computer varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time the solenoid energizes. The engine computer adjusts solenoid pulse width based on engine air flow.

A rubber boot covers the duty cycle EVAP purge solenoid. The solenoid attaches to a bracket mounted to the right engine mount. The top of the solenoid has the word TOP on it. The solenoid will not operate unless it is installed correctly.

Canister Purge Function

The Premier engine (2.5L Premier) use a venturi in the air cleaner assembly to provide vacuum to purge the lines. The effect of the venturi increases the speed of the intake air flowing by the purge inlet slots in the venturi wall. This creates a low pressure area at the inlet slots that draws vapors from the canister into the airstream flowing through the venturi. The vapors pass through the intake manifold into the combustion chambers where they are consumed during combustion.


Fuel Tank Pressure Relief and Rollover Valve
  1. Disconnect the negative battery cable from the battery.
  3. Remove the fuel filler cap and drain the fuel tank using a portable gasoline siphon/storage tank. Drain the tank until it is completely empty.
  5. Remove the fuel tank from the car. Refer to Fuel System for this procedure.
  7. The rollover valve is seated in a grommet. Remove by prying one side upward and then roll the grommet out of the tank.

To install:
  1. Start one side of a new grommet into the opening in the fuel tank and roll the grommet into place. Using finger pressure only, press the valve/grommet into place. A light coat of power steering fluid or a spray of silicon lubricant may be used to ease installation.
  3. Install the fuel tank as per instructions found in this information.
  5. Fill the fuel tank and install the fuel tank filler cap.
  7. Connect the negative battery cable.
  9. Start the vehicle and check for any fuel leaks.

When starting the vehicle after removal of any fuel system component, it will take longer for the vehicle to start because of the system having to pressurize itself.


Release the fuel system pressure before servicing the fuel system components. Service the vehicle in a well ventilated area and avoid ignition sources. Never smoke while servicing the vehicle.

  1. Remove the fuel tank. Refer to Fuel System for this procedure.
  3. Wedge the blade of a thin prytool between the rubber grommet and the fuel tank where the support rib is located.

Do not wedge between the valve and the grommet. This could damage the valve during removal.

  1. Use a second prytool as a support to pry the valve and grommet assembly from the tank.
  3. Place the valve upright on a flat surface. Push down on the grommet and peel it off of the valve.

To install:
  1. Install the rubber grommet in the fuel tank by working it around the curled lip of the tank.

Only use power steering fluid to lubricate the pressure relief/rollover valve grommet.

  1. Lightly lubricate the grommet with power steering fluid only and push the valve downward into the grommet. Twist the valve until properly positioned.
  3. Install the fuel tank. Refer to Fuel System for this procedure.
  5. Connect the negative battery cable.
  7. Start the vehicle and check for any fuel leaks.

When starting the vehicle after servicing any part of the fuel system, it will take longer for the engine to start because the system will need to repressurize itself.