DESCRIPTION
The fuel evaporation system is used to prevent fuel vapor from entering the atmosphere. Activated charcoal in the carbon canister adsorbs fuel vapor given off by the fuel system.
The system consists of a fuel tank with integral expansion tank, vacuum relief filler cap, charcoal canister, purge control valve, fuel check valve, canister purge and vacuum signal lines, and vapor vent lines.
OPERATION
Fuel vapor from the sealed fuel tank is stored in the charcoal canister when the engine is stopped or idling. As the throttle valve opens and engine speed increases, vacuum opens the purge control valve and fuel vapors are drawn from canister into the intake manifold.
On Pickup with fuel injected 2.4L engine, a thermal vacuum valve prevents any purging of canister by preventing the opening of the purge valve when coolant temperature is below 140°F/60°C.
When the purge valve is closed a small amount of purge air flows into intake manifold through the constant purge orifice.
On carburetted Pickup models, a vent switching valve allows carburetor float bowl to vent into canister when engine is not running.
MAINTENANCE
Every 30,000 miles or every 2 years, test fuel vapor vent line. Inspect all vapor hoses and lines for damage, deterioration, and leaks.
FUEL TANK & VAPOR VENT LINE
- Check all hoses and fuel filler cap for leaks. Disconnect fuel tank vapor hose at canister. Connect a "T" fitting, manometer, and shut-off valve to end of hose. (Scheme 17)
- Slowly apply air pressure to open shut-off valve until manometer indicates 15 3/4" (400 mm) water. Close shut-off valve and remove air supply.
- Fuel tank and hoses should hold this pressure within 1" (25 mm) of water for 2 1/2 minutes. If pressure does not hold, repair or replace components as necessary.
- If pressure holds for 2 1/2 minutes, remove fuel filler cap and check that pressure drops. If pressure does not drop, check hoses and lines for obstructions.
Testing Fuel Vapor Vent Line. Scheme 17
CANISTER PURGE CONTROL VALVE
Remove hose from valve port and blow through hose. Air should pass through purge and vent lines, but not through vacuum lines.
FUEL CHECK VALVE
Disconnect hoses and blow air through valve at fuel tank inlet port. There should be significant resistance. Repeat on engine inlet side of valve. Air should flow freely through valve. Replace valve if it does not operate as outlined.
VACUUM RELIEF FILLER CAP
Wipe cap clean and apply vacuum from tank side. Slight resistance should be felt and the cap should make distinct clicking noises. As vacuum increases, resistance should decrease and clicking noise should disappear. If cap does not perform as outlined, replace cap.