The Evaporative Emission Control (EVAP) system is designed to prevent fuel tank vapors from being emitted into the atmosphere. When the engine is not running, fuel vapors from the tank are stored in a charcoal canister. The charcoal canister absorbs the vapors and stores them until certain engine conditions are met and the vapors can be purged and burned by the engine. In some vehicles, any liquid fuel entering the canister goes into a reservoir in the bottom of the canister to protect the integrity of the carbon element in the canister above. These systems employ the following components:
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. This can be done by applying a THIN film of petroleum jelly on the lip of the filler tube. If the jelly transfers evenly to the gasket, the seal is probably OK. If the gasket is missing or damaged, replace the cap or gasket as necessary.
EXCEPT 5S-FE WITH AUTOMATIC TRANSMISSION
- Remove the charcoal canister from the vehicle.
- Visually check the charcoal canister for cracks or damage.
- Check for a clogged filter and stuck check valve. Using low pressure compressed air (0.68 psi. or 4 kPa), blow into the tank pipe (A) and check that the air flows without resistance from the other pipes. If this does not test positive replace the canister.
- Clean the filter in the canister by blowing no more than 43 psi (294 kPa) of compressed air into the pipe (A) to the outer vent control valve while holding the other upper canister pipes (B) closed.
- Replace or reinstall the canister as needed.
- Disconnect the EVAP hoses from the charcoal canister.
- Visually inspect the canister for cracks or leaks.
- Install a plug to port E.
- While holding port B closed, blow air into port A and check that air flows from port D.
- While holding port B and port D closed, blow air into port A and check that air does not flow from port C.
- Apply vacuum with a pump to port B and check that vacuum does not decrease when port C is closed, and check that the vacuum decreases when port C is released.
- While holding port C closed, apply vacuum to port A and check that air flows into port B. If a problem is found, replace the canister.
- Remove the plug. Reconnect the vacuum hoses.
- Drain and recycle the engine coolant.
- Remove the BVSV.
- Cool the BVSV to below 95-104° F (35-40° C) with cool water. Blow air into pipe and check that the BVSV is closed.
- Heat the BVSV to above 129° F (54° C) with hot water. Blow air into pipe and check that the BVSV is open. If a problem is found, replace the valve.
- Apply liquid sealer to the threads of the BVSV and reinstall.
- Refill the radiator with the proper amount of water coolant mixture.
- Remove the TVV valve from the engine.
- Cool the valve to below 95-104° F (35-40° C) with cool water.
- Make sure that air does not flow from the upper port to the lower port.
- Heat the TVV to above 129° F (59° C) with hot water.
- Check that air flows from the upper port to the lower port of the valve. If the operation is not as specified, replace the TVV valve.
Label and disconnect the lines running to the canister. Remove the fasteners, then remove the charcoal canister from the vehicle. Do not attempt to wash the charcoal canister. Installation is the reverse of removal.Bimetal Vacuum Switching Valve (BVSV)
- Drain the engine coolant from the radiator into a suitable container.
- Unscrew the BVSV from the engine.
- Apply liquid sealer to the threads of the BVSV. Carefully thread the valve into the engine.
- Fill the radiator with coolant. Start the engine, check and top off the fluid level.
- Drain the coolant the from the radiator.
- Disconnect the vacuum hoses from the charcoal canister (lower-2) and throttle body (upper-1).
- Remove the TVV valve from the engine.
- Apply adhesive to 2 or 3 of the threads of the TVV, then tighten the valve to 22 ft. lbs. (29 Nm).
- Reattach the vacuum hoses.
- Refill the engine with coolant. Start the engine, check and top off the fluid level.