DESCRIPTION
The fuel evaporation system is used to prevent fuel vapor from entering the atmosphere. Activated charcoal in the carbon canister absorbs fuel vapor.
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.
Scheme 1
Scheme 2
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 Pulsar NX and Sentra models, the control unit closes the canister control solenoid valve to prevent any purging of the canister by preventing the opening of the purge valve when coolant temperature is less than 140°F (60°C), as relayed to the control unit from the thermal vacuum valve.
On all other models, when the purge valve is closed, a small amount of purge air flows into intake manifold through the constant purge orifice.
Scheme 3
Scheme 4
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. Attach "T" fitting, manometer, and shut-off valve to hose. (Scheme 5)
- Slowly apply air pressure to open shut-off valve until manometer indicates 15 3/4" (400 mm) water. Close shut-off valve. Remove air supply.
- Fuel tank and hoses should hold this pressure within 1" (25 mm) of water for 2 1/2 minutes. If not, repair or replace components as necessary.
- If pressure holds for 2 1/2 minutes, remove fuel filler cap. Check that pressure drops. If not, check hoses and lines for obstructions.
Scheme 5
CARBON CANISTER
Remove hose from valve port. Blow through hose. Air should pass through purge and vent lines, but not through vacuum lines. (Scheme 6)
Scheme 6
FUEL CHECK VALVE
Disconnect hoses. Blow air through valve at fuel tank inlet port. There should be significant resistance felt, and a portion of airflow directed toward fuel tank. Repeat on engine inlet side of valve. Air should flow freely through valve. If air doesn't flow freely, replace check valve.
VACUUM RELIEF FILLER CAP
Wipe cap clean. 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 tests incorrectly in either case, replace it.