To prevent hydrocarbon emissions from entering the atmosphere, all vehicles use evaporative emission control (EEC or EVAP) 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. 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
CHECKING THE FILLER CAP
See Figure 1
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.
CHECKING THE PURGE CONTROL VALVE
This valve is used only on 1970-71 engines which are also equipped with an air injection system
- Disconnect the line which runs from the storage case to the valve, at the valve end.
- Connect a tachometer to the engine in accordance with the manufacturer's instructions.
- Start the engine and slowly increase its speed until the tachometer reads 2,500 rpm (transmission in Neutral).
- Place a finger over the hose fitting (storage case-to-valve) on the valve.
- If there is no suction, check the air pump for a malfunction. If the air pump is not defective, replace the valve.
INSPECTING THE CHARCOAL CANISTER AND CHECK VALVES
See Figures 2 and 3
Remove the charcoal canister from the engine compartment and visually inspect it for cracks or other damage.
Check for stuck check valves. All models from 1972-78 have one check valve in the line between the fuel tank and the charcoal canister. It is located in the trunk. To check:
- Remove the check valve from the line.
Mark which end goes toward the fuel tank and which end goes toward the charcoal canister
- Blow into the fuel tank end. A slight resistance should be felt at first.
- Blow through the other end. No resistance should be felt at all.
- If your results differ from those above, the check valve will require replacement.
Later models have two or three check valves, all are located in the charcoal canister. To check:
- Using low pressure compressed air, blow into the tank pipe. The air should flow from the other pipes without resistance.
- If the air flow is incorrect, the check valve will require replacement. Before installing the canister, clean the filter. Blow compressed air into the purge pipe while keeping the others blocked with your fingers.
Do not attempt to wash the charcoal canister. While cleaning the canister, under no circumstances should any activated charcoal be removed
EEC System Troubleshooting
Before embarking on component removal or extensive diagnosis, perform a complete visual check of the system. Every vacuum line should be inspected for cracking, loose clamps and obstructions
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 tester or equivalent type tester. Run the test probe along the lines and connections. The meter will indicate the presence of a leak by a high hydrocarbon (HC) reading.
- 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 pinches 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 the mount. Blow into the relief valve housing. If the cap passes pressure with light blowing or if it fails to release with hard blowing, it is defective and must be replaced.
Use the proper cap for the type of system used; either a sealed cap or safety valve cap, as requiredOuter Vent Control Valve
- Disconnect the hoses from the valve.
- Check that the valve is open when the ignition switch is turned OFF .
- Check that the valve is closed when the ignition switch is in the ON position.
- If the valve doesn't operate properly, check the fuse and wiring, if OK, replace the valve.
- Drain the radiator and save the coolant.
- Remove the thermoswitch from the intake manifold. Cool the switch to below 109°F (43°C).
- Use an ohmmeter and check for continuity; it should exist.
- Heat the switch with hot water to a temperature above 131°F (55°C). There should be no continuity.
- Apply liquid sealer to the threads of the switch and then reinstall it in the manifold.
- Refill the coolant.