To prevent hydrocarbon emissions from entering the atmosphere, Toyota vehicles use Evaporative Emission Control (EEC) systems. Models produced between 1970 and 1971 use a case storage system, while later models use a charcoal canister storage system.
The major components of the case storage system are a purge control or vacuum switching valve, a fuel vapor storage case, an air filter, a thermal expansion tank, and a special fuel tank.
When the vehicle is stopped or the engine is running at a low speed, the purge control or vacuum switching valve is closed. Fuel vapor travels only as far as the case where it is stored.
When the engine is running at a high speed (cruising speed), the purge control valve is opened by pressure from the air pump or else the vacuum switching valve opens, depending upon the type of emission control system used (see the Evaporative Emission Control System Usage chart). This allows the vapor stored in the case to be drawn into the intake manifold along with fresh air which is drawn in from the filter.
The charcoal canister storage system functions in a similar manner to the case system, except that the fuel vapors are stored in a canister filled with activated charcoal, rather than in a case, and that all models use a vacuum switching valve to purge the system. The air filter is not external as it is on the case system. Rather, it is an integral part of the charcoal canister.
REMOVAL & INSTALLATION
Removal and installation of the various evaporative emission control system components consists of unfastening hoses, loosening securing screws, and removing the part which is to be replaced from its mounting bracket. Installation is the reverse of removal.
When replacing any EEC system hoses, always use hoses that are fuel-resistant or are marked "EVAP".
EEC System Troubleshooting
There are several things which may be checked if a malfunction of the evaporative emission control system is suspected.
- Leaks may be traced by using a hydrocarbon tests. Run the test probe along the lines and connections. The meter will indicate the presence of a leak by a high hydrocarbon (HC) reading. This method is much more accurate than visual inspection which would only indicate the presence of a leak large enough to pass liquid.
- Leaks may be caused by any of the following:
- Defective or worn hoses
- Disconnected or pinched hoses
- Improperly routed hoses
- A defective filler cap or safety valve (sealed cap system)
If it becomes necessary to replace any of the hoses used in the evaporative emission control system, use only hoses which are fuel-resistant or are marked "EVAP."
- If the fuel tank, storage case or thermal expansion tank collapses, it may be the fault of clogged or pinched vent lines, a defective vapor separator, or a plugged or incorrect filler cap.
- To test the filler cap (if it is the safety valve type), clean it and place it against your mouth. Blow into the relief valve housing. If the cap passes pressure with light blowing, or fails to release with hard blowing, it is defective and must be replaced.
Use the proper cap for the type of system in your car. Either a sealed cap or safety valve cap is required.Purge Control Valve
1970-71 MODELS WITH AIR INJECTION
- Disconnect the line which runs from the storage case to the valve, at the valve.
- Connect a tachometer to the engine, according to the manufacturer's instructions.
- Start the engine, set the parking brake, place the transmission in neutral and slowly increase engine speed to 2,500 rpm.
- Place your finger over the hose fitting on the valve.
- If there is no vacuum felt, the air pump is probably defective. If the air pump is good, replace the valve.
The purge control valve is connected to a carburetor port, which is located above the throttle control valve. When the engine is stopped or at idle, there is no vacuum signal at the purge control valve, so, it remains closed.
When the throttle valve opens, the carburetor port is uncovered and a vacuum signal is sent to the purge control valve, which opens and allows vapors stored in the canister to be pulled into the carburetor.
- Note the routing of the vacuum lines and remove the canister from the car.
- Place your finger over the purge control valve opening, located at the center of the canister on its top side.
- Gently blow through the vapor intake. No resistance should be felt.
- Uncover the purge control valve opening and blow through it. No air should come out of the vapor intake or the bottom of the canister.
- If the purge control valve fails either test, replace the canister. If the valve is okay, put the canister back in the car.
- If the valve once again, appears to be malfunctioning after installation, you have either defective vacuum lines or a clogged carburetor port.
The check valve is located in the line which runs from the fuel tank or vapor separator, to the canister. On all 1973 models, it is located in the trunk. On all other models, it is in the engine compartment, near the canister.
- Remove the check valve from the fuel tank-to-canister line.
- Blow into the fuel tank end. A slight resistance should be felt at first.
- Blow through the canister end. No resistance should be felt.
- If the check valve is defective, replace it.