Used on all engines.
This system reduces hydrocarbon emissions by storing and routing evaporated fuel from the fuel tank and the carburetor's float chamber (carbureted engines only) through the charcoal canister to the intake manifold for combustion in the cylinders at the proper time.
When the ignition is OFF, hydrocarbons from the carburetor float chamber pass through the control valve into the canister. Fuel vapors from the fuel tank pass into the charcoal canister through a check valve located on the canister.
When the ignition is switch ON, but the engine is NOT running, the control valve is energized blocking the movement of fuel vapor from the carburetor's float chamber. Vapors from the fuel tank can still flow and be stored in the charcoal canister.
With the engine running above 1,500 rpm, the fuel vapors are purged from the canister into the intake manifold. If deceleration occurs, the throttle position switch opens (disconnects) and the ECM detects the change. The control valve is de-energized and the purging of vapor is stopped. This eliminates the delivery of excess fuel vapor during periods of poor or reduced combustion.
When there is pressure in the fuel tank (such as from summer heat or long periods of driving) the canister valve opens, allowing vapor to enter the canister and be stored for future delivery to the engine.
Before embarking on component removal or extensive diagnosis, perform a complete visual check of the system. Every vacuum line and vapor line (including the lines running to the tank) should be inspected for cracking, loose clamps, kinks and obstructions. Additionally, check the tank for any signs of deformation or crushing. Each vacuum port on the engine or manifold should be checked for restriction by dirt or sludge.
The evaporative control system is generally not prone to component failure in normal circumstances; most problems can be tracked to the causes listed above.Fuel Filler Cap
Check that the filler cap seals effectively. Remove the filler cap and pull the safety valve outward to check for smooth operation. Replace the filler cap if the seal is defective or if it is not operating properly.Charcoal Canister
Check the canister using the procedures described in Routine Maintenance .
Do not attempt to wash the charcoal canister. Also be sure that no activated carbon comes out of the canister during the cleaning process.Outer Vent Control Valve
See Figures 1, 2, 3 and 4
Used on 3A-C and 3E engines.3A-C ENGINES
- Label and disconnect the hoses from the control valve but leave the wiring for the valve connected.
- Check that the valve is open by blowing air through it when the ignition switch is in the OFF position.
- Check that the valve is closed when the ignition switch is in the ON position.
- Reconnect the hoses to the proper locations. If the valve doesn't operate correctly, double check the fuse and wiring before replacing the valve.
- Label and disconnect the wires and hoses from the control valve.
- Apply battery voltage to the terminals and check that the valve is closed by blowing air through it.
- Check that the valve is closed below 115°F(46°C) or open above 140°F(60°C) without voltage applied to the terminals.
- Reconnect the hoses to the proper locations. If the valve doesn't operate correctly, double check the wiring before replacing the valve.
See Figures 5 and 6
Used on 3A-C and 3E engines.
- Drain the coolant from the radiator into a clean container.
- Remove the thermoswitch.
- Cool the switch off until the temperature is below 109°F (43°C) on 3A-C engines or 118°F (48°C) on 3E engines. Check that there is continuity through the switch by the use of an ohmmeter.
- Using hot water, bring the temperature of the switch to above 131°F (55°C) on 3A-C engines or 140°F (60°C) on 3E engines. Check that there is no continuity when the switch is above this temperature.
- Apply sealer to the threads of the switch and reinstall it.
- Refill the radiator with coolant.
See Figures 7, 8, 9 and 10
Used on 3A-C and 3E engines.
- Connect battery voltage to the terminals of the EVAP vacuum switching valve (VSV).
- Blow air into the pipe and check that it is open.
- Remove the voltage source from the terminals and check that the valve is closed.
- Using an ohmmeter, check that there is no continuity between the positive terminal and the VSV body. If there is continuity, replace the valve.
- Using an ohmmeter, measure the resistance between the two terminals. It should be between 38-44- at 68°F (20°C). If not, replace the valve.
See Figures 11 and 12
Used on 3A-C engines.
- Using an ohmmeter, check for continuity between the switch terminal and body with the engine off and cold.
- Start the engine and warm it to normal operating temperature.
- Check that there is no continuity between the switch terminal and body.
REMOVAL & INSTALLATION
See Figure 13
Removal and installation of the various evaporative emission control system components consists of labeling or marking and unfastening hoses, loosening retaining screws, and removing the part which is to be replaced from its mounting point.
When replacing any EVAP system hoses, always use hoses that are fuel-resistant or are marked EVAP. Use of hose which is not fuel-resistant will lead to premature hose failure.