See Figures 1 through 7
This system is designed to prevent hydrocarbons from escaping into the atmosphere from the fuel tank, due to normal evaporation.
The parts of the system are:
Be sure that all hoses are clamped and not dry-rotted, hard or broken. Replace any suspect hoses2-way Valve
This device, sometimes mistaken for a fuel filter, is found in the vapor line running from the tank to the canister. Located at or near the tank, this valve is both a pressure- and suction-sensitive unit. Its purpose is to compensate for the pressure changes within the fuel tank. (Since the filler cap is tight enough to be considered sealed, the pressure must be equalized somewhere within the system.
When the pressure builds within the tank, such as on a very hot day or after a long period of driving, the valve releases the pressure and vapor into the charcoal canister, thereby venting the tank without raising emissions. Conversely, should the tank develop a vacuum, the valve will bleed some air (and vapor) from the canister into the tank.TIP:
If you've heard a ghostly, high-pitched whining noise from the rear of your car on a summer day (even with the engine off), you're hearing this valve releasing pressure. Two ways to prevent the noise (for a while) are to either loosen the gas cap and then retighten it after the pressure equalizes or keep the tank 1 / 2 - 3 / 4 full of fuel. Replacing the valve may change the sound but rarely eliminates it.
The control pressures within the valve are pre-set and not adjustable, but a quick check can be performed as follows:
- Look at the valve and observe which end is toward the tank. Label or diagram the correct position.
- Remove the valve from the vapor line. It may be necessary to remove other obvious components such as a parking brake cable bracket for access.
- Lightly blow through either end of the valve. If air passes after some resistance, the valve is in good condition.
- Install the valve into the line in the correct direction and secure the clamps. Make certain the lines are firmly seated on the ports before installing the clamps.
See Figures 8 through 19
First check all the hoses and connections for proper attachment, cracks, bends and leaks. Many problems relate simply to poor mechanical connections within the system or restricted hoses.VACUUM TEST
- Disconnect the vacuum hose (red stripes) from the throttle body and connect it to a hand-held vacuum pump. Plug the nipple from which the hose was removed.
- Allow the engine to cool completely, or, with a cold engine, apply 14.8 in.Hg vacuum. The vacuum should hold.
- Start the engine and allow it to idle. Increase engine speed to 3,00 rpm. Vacuum should hold throughout this range. The engine temperature should not exceed 140°F (60°C) for this test.
- Allow the engine to idle until engine temperature exceeds 158°F (70°C). Vacuum should hold at idle. Shut the engine off.
- With 14.8 in.Hg vacuum applied and the engine temperature still above 158°F (70°C), start the engine and increase engine speed to 3,000 rpm within 3 minutes. A vacuum leakdown should occur. Return the engine to idle.
- Reapply vacuum and, after 3 minutes, return the engine to 3,000 rpm. Vacuum should be held momentarily, then leakdown.
At altitudes above 7,200 ft. (2,200 m), Step 6 does not apply.ELECTRICAL TEST
- Disconnect the vacuum hoses from the valve.
- Disconnect the wiring harness from the valve
- Connect a hand-held vacuum pump to the nipple from which the red striped hose was removed and apply 14.8 in.Hg vacuum. Vacuum should hold.
- Using a jumper wire connected to a 12 volt source, apply battery voltage as shown in the accompanying illustration. Vacuum should leakdown.
- With an ohmmeter, check the resistance between the valve terminals. Resistance should be 36-44 68°F (20°C).
- If the valve fails any test, it should be replaced.
REMOVAL & INSTALLATION
The canister or canisters used on these models is replaced periodically. No other maintenance is necessary except for an occasional check of connecting hose condition. To replace the canister:
- Remove the two connecting hoses from the canister.
- Loosen and remove the canister retaining band bolt.
- Remove the canister.
- Install the canister and connect the hoses. Replace any brittle hoses.