See Figures 1 and 2
During system operation, fuel vapors and/or liquid are routed to the liquid/vapor separator or check valve, where liquid fuel is directed back into the fuel tank as fuel vapors flow into the charcoal filled canister. The charcoal absorbs and stores the fuel vapors when the engine is not running or at idle. When the throttle plates are opened, vacuum from above the throttle plate (ported vacuum) is routed through a vacuum signal line, to the purge control valve on the canister. The control valve opens, the fuel vapors move from the canister through a purge line, into the intake manifold and the combustion chambers.
All models use a sealed fuel tank, carbon canister/vapor vent line, fuel check valve, vacuum signal line, a canister purge line and a fuel tank vacuum relief valve. Carbureted engines have an additional vent line and switching valve, which are connected to the carburetor float bowl vent. Depending on the specific application, the system will use either thermal control valve or a purge control valve/solenoid, to prevent system operation during engine warm-up. Early systems use a thermal control valve to close off the vacuum signal to the purge control valve until engine temperature is above 122°F (50°C). On later systems, this function is controlled by the ECM, through the EGR/Canister Control Solenoid. The ECM also prevents operation during idle and when high engine speeds.
Check the hoses for proper connections and damage. Replace as necessary. Check the vapor separator tank for fuel leaks, distortion and dents, then replace as necessary.EVAP Carbon Canister/Purge Control Valve
The carbon canister has an air filter in the bottom of the canister. The filter element should be checked once a year or every 12,000 miles (19,000 km); more frequently if the car is operated in dusty areas. Replace the filter by pulling it out of the bottom of the canister and installing a new one.
- Disconnect the rubber hose between the canister control valve and the T-fitting, at the T-fitting.
- Apply vacuum to the hose leading to the control valve (upper vacuum port).
- The valve should hold vacuum indefinitely. If the control valve leaks, remove the top cover of the valve and check for a dislocated or cracked diaphragm. If the diaphragm is damaged, a repair kit containing a new diaphragm, retainer and spring is available, replace it.
See Figure 3
- Disconnect the canister and remove if necessary.
- Blow air into port A and ensure that there is no leakage.
- Blow air into ports B and ensure that there is leakage.
See Figure 4
- Disconnect the canister and remove if necessary.
- Blow air into port A and ensure that there is no leakage. If leakage occurs, replace the canister assembly.
- Apply 4-6 in. Hg (13.5-20 kPa) of vacuum to port A .
- Cover port D with your hand while blowing air into port C . Air should flow freely from port C to port B .
- If the canister/purge valve assembly does not perform as specified, replace the assembly.
This solenoid cuts the vacuum to the EGR valve and EVAP purge valve on the charcoal canister off at both low and high RPM. For testing information refer to EGR Control Solenoid testing information found in this Section.EVAP Thermal Vacuum Valve
This valve cuts the vacuum to the EGR valve, EVAP purge valve and the distributor during cold engine operation. For testing information refer to EGR Thermal Vacuum Valve testing information found in this section.EVAP Vent Switching Valve
- Disconnect the rubber hose from the vent valve control port (upper vacuum port).
- Apply vacuum to the hose leading to the control valve.
The valve should hold vacuum indefinitely.
If the valve holds vacuum, proceed to the next step.
- Disconnect the vent line from the carburetor float bowl.
- Connect a vacuum pump to the switching valve vent line port.
- With the engine OFF , apply vacuum to vent line hose. The valve should NOT hold vacuum.
- Start the engine and apply vacuum to the to the vent line, vacuum should hold.
- Replace the Vent switching valve if it does not perform as specified.
See Figure 5
Wipe the valve housing clean. Suck air through the cap. A slight resistance indicates that the valve is in good condition. Resistance should disappear when the valve clicks. If the valve is clogged or if no resistance is felt, replace the fuel cap.Fuel Check Valve
See Figures 6 and 7
- Blow air through the connector on the tank side. A considerable resistance should be felt and a portion of air flow should be directed toward the canister.
- Blow air through the connector on the canister side. Air flow should be smoothly directed toward the fuel tank.
- If the valve does not perform as specified replace the fuel check valve.
If the valve is equipped with an internal rollover valve, test the rollover function as follows:
- Tilt the valve to 90° and repeat Steps 1 and 2.
- Tilt the valve to 180° and repeat Steps 1 and 2.
- Air should not be allowed to pass in either test. If air does pass when the valve is rotated, replace the fuel check valve assembly.
REMOVAL & INSTALLATION
Removal and installation of the various evaporative emission control system components consists of tagging and disconnecting the hoses from the component. Remove the component by loosening retaining screws and removing the part. Install in the reverse order. When replacing hose, make sure that it is fuel and vapor resistant.