See Figure 1
Fuel vapors trapped in the sealed fuel tank are vented through the Evaporative Emission Valve orifice in the top of the tank. The vapors leave the valve assembly through a single vapor line and continue through the Vapor Control Valve to the Evaporative Emission Canister for storage until they are purged to the engine for burning.
Purging removes the fuel vapor stored in the canister. The fuel vapor is purged via a Vapor Management Valve (VMV) or vacuum controlled purge valve. Purging occurs when the engine is at normal operating temperature and off idle.Evaporative Emissions Canister
The fuel vapors from the fuel tank are stored in the fuel vapor canister until the vehicle is operated, at which time, the vapors will purge from the canister into the engine for consumption. The fuel vapor canister contains activated carbon, which absorbs the fuel vapor. The canister is located in the engine compartment or along the frame rail.Evaporative Emission Valve
Fuel vapors in the tank are vented through the Evaporative Emission Valves in the top of the fuel tank. The vapors are transmitted through a single vapor tube to the canister at the front of the vehicle. A spring loaded poppet valve provides relief ahead of the orifice to the canister. This valve gradually opens above 20-25 in. Hg (5-6 kPa) to vent fuel vapors to the canister.Vapor Control Valve
The vapor system also includes an inline vapor control valve mounted centrally on the top of the fuel tank. During refueling, the valve inhibits flow of vapor through the vapor valves to keep the tank from overfilling.Vapor Management Valve (VMV)
The VMV is inline with the carbon canister and controls the flow of fuel vapors out of the canister. It is normally closed. When the engine is OFF , the vapors from the fuel tank flow into the canister. After the engine is started, the solenoid is engaged and opens, purging the vapors into the engine. With the solenoid open, vapors from the fuel tank are routed directly into the engine.Pressure/Vacuum Relief Fuel Tank Filler Cap
The fuel cap contains an integral pressure and vacuum relief valve. The vacuum valve acts to allow air into the fuel tank to replace the fuel as it is used, while preventing vapors from escaping the tank through the atmosphere. The vacuum relief valve opens after a vacuum of 0.25 psi (1.7 kPa). The pressure valve acts as a backup pressure relief valve in the event the normal venting system is overcome by excessive generation of internal pressure or restriction of the normal venting system. The pressure relief is 2 psi (14 kPa). Fill cap damage or contamination that stops the pressure vacuum valve from working may result in deformation of the fuel tank.
Evaporative Emissions Canister
Generally, the only testing done to the canister is a visual inspection. Look the canister over and replace it with a new one if there is any evidence of cracks or other damage.Evaporative Emissions Valve
Inspect the valve for open air passage through the orifice. The valve is molded directly to the fuel tank and is not serviceable separately. If the orifice is blocked, replace the fuel tank.Vapor Management Valve (VMV)
See Figure 2
- Remove the VMV.
Measure the resistance between the two VMV terminals.
- If the resistance is between 30-36 ohms, proceed to the Step 3.
- If the resistance is not between 30-36 ohms, replace the VMV.
Attach a hand-held vacuum pump to the intake manifold vacuum side of the VMV, then apply 16 in. Hg (53 kPa) of vacuum to the solenoid.
- If the solenoid will not hold vacuum for at least 20 seconds replace it with a new one.
- If the solenoid holds vacuum, proceed to Step 4. Keep the vacuum applied to the solenoid.
Using an external voltage source, apply 9-14 DC volts to the VMV electrical terminals.
- If the solenoid opens and the vacuum drops, the solenoid is working properly. Check power and ground circuits.
- If the solenoid does not open and the vacuum remains, replace the solenoid is faulty.
REMOVAL & INSTALLATION
Evaporative Emissions Canister
See Figure 3
- Disconnect the vapor hose from the canister.
- Remove the bolt retaining the canister and bracket assembly to the frame rail.
- Lift the canister to disengage the tab on the back side of the canister and remove from the vehicle.
- Installation is the reverse of removal. Tighten bolt to 17-20 ft. lbs. (22-28 Nm)
Evaporative Emissions Valve
The valve is an integral part of the fuel tank and is not serviceable separately. If replacement is required, the valve must be replaced as part of the fuel tank assembly.Vapor Control Valve
- Remove the fuel tank.
- Disconnect the vapor hose from the valve.
- Remove the valve.
- Installation is the reverse of removal.
Vapor Management Valve (VMV)
See Figure 4
- Remove the cowl top vent panel.
- Disconnect the electrical harness from the VMV.
- Disconnect the fuel vapor hoses.
- Loosen the two nuts securing the valve and remove from the vehicle.
- Installation is the reverse of removal. Tighten the nuts to 98-115 inch lbs. (11-13 Nm).