Nissan Pick-ups and Pathfinder 1989-1995

Evaporative Emission Control System

Print

OPERATION



See Figure 1

When raw fuel evaporates, the vapors contain hydrocarbons. To prevent these fumes from escaping into the atmosphere, the fuel evaporative emission control system was developed.

The evaporative emission control systems used on Nissan trucks consists of a sealed fuel tank, a vapor/liquid separator, a vapor vent line, a carbon canister, a vacuum signal line and a canister purge line.

In operation, fuel (vapor and liquid) is 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 is at idle. When the throttle vacuum rises, the vacuum from above the throttle valves is routed through a vacuum signal line to the purge control valve on the canister. The control valve opens and allows the fuel vapors to be drawn from the canister through a purge line and into the intake manifold and the combustion chambers.



Click image to see an enlarged view

Fig. Fig. 1: Evaporative emission control system

TESTING



See Figures 2, 3, 4 and 5

Check the hoses for proper connections and damage. Replace as necessary. Check the vapor separator tank assembly for fuel leaks, distortion and dents, and then as necessary.



Click image to see an enlarged view

Fig. Fig. 2: Check the hoses and vapor vent lines on the canister assembly



Click image to see an enlarged view

Fig. Fig. 3: The evaporative emissions canister should be checked using its vacuum/vapor ports



Click image to see an enlarged view

Fig. Fig. 4: Checking the fuel tank vacuum relief valve



Click image to see an enlarged view

Fig. Fig. 5: Checking the fuel check valve

Carbon Canister and Purge Control Valve

To check the operation of the carbon canister purge control valve, disconnect the rubber hose between the valve and the T-fitting, at the T-fitting. Apply vacuum to the hose leading to the control valve. The vacuum condition should be maintained 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 and should be installed.

Fuel Tank Vacuum Relief Valve

See Figure 4

  1. Remove the gas cap and wipe clean the valve housing (which is located in the cap).
  2.  
  3. Draw air through the bottom of the cap. A slight resistance (and a clicking noise) indicates that the valve is OK.
  4.  
  5. If no resistance is felt or if you hear no clicking noise, replace the cap.
  6.  

Fuel Check Valve

See Figure 5

  1. Locate the valve in the fuel line and remove it.
  2.  
  3. Blow air though the connector on the fuel tank side. You should notice a considerable amount of resistance and some of the air should be deflected to the evaporative canister.
  4.  
  5. Now blow air through the connector on the canister side. There should be no obstructions and the air should flow toward the fuel tank.
  6.  
  7. If the valve does not work properly in both tests, it should be replaced.
  8.  
  9. Install the valve in the fuel line.
  10.  

ADJUSTMENTS



No adjustment are either necessary or possible

REMOVAL & INSTALLATION



Removal and installation of the various evaporative emission control system components consists of disconnecting the hoses, loosening any retaining screws, and removing the part which is to be replaced or checked. Installation should then be obvious. When replacing hoses, make sure that they are fuel and vapor resistant.

 
label.common.footer.alt.autozoneLogo