Nissan Z - ZX 1970-1988 Repair Guide

Evaporative Emission Control System

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See Figures 1 and 2



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Fig. Fig. 1: Typical evaporative emission control system-1970-73 models



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Fig. Fig. 2: Typical evaporative emission control system-1974-88 models

OPERATION



The evaporative emission control system employs:



A sealed filler cap.
 



A vapor/liquid separator and vent line.
 



A flow guide valve (240 Z).
 



An evaporation control tube (240 Z).
 



A carbon storage canister (260 Z, 280 Z/ZX and 300 ZX).
 



A fuel check valve (1976-88 models).
 

The sealed filler cap allows vacuum (created as the fuel pump empties the tank) to draw air into the tank to replace the used fuel. This avoids damaging the tank or starving the fuel system. It will not, however, allow fuel vapor to escape.

The vapor/liquid separator allows a vent line to collect the vapor formed in the gas tank and store it in the crankcase or in a carbon canister but prohibits liquid fuel from passing into the vent line.

The flow guide valve allows vapor stored in the crankcase to be drawn into the intake manifold when the engine is operated, while shunting fuel vapor to the crankcase and closing off the line to the manifold when the engine is stopped.

The evaporation control tube carries the fuel vapor from the crankcase when the engine is stopped.

The carbon canister stores the fuel vapor from the tank when the engine is not running. When the engine starts, vacuum carried by a vacuum signal line opens a purge valve on the top of the canister. Air is then drawn through a filter on the bottom of the canister, through the charcoal via a nozzle in the purge valve and into the manifold.

The fuel check valve, installed in the vapor line between the fuel tank and the carbon canister, allows air flow into the fuel tank but prevents vapor flow to the canister except under high vacuum.

INSPECTION



Fuel Tank Filler Cap and Vent Line

See Figure 3

  1. Periodically inspect the hoses and the fuel tank filler cap for cracks or other deficiencies and replace the parts, as necessary. When inspecting the filler cap, pull the pressure relief valve outward to check for free, smooth operation. Check that it seals effectively. Replace the defective parts as necessary.
  2.  



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Fig. Fig. 3: Fuel filler cap

  1. Disconnect the vapor vent line at the canister or the flow guide valve. Install a T-connector providing a source of air pressure and a pressure gauge which reads in inches of water.
  2.  
  3. Slowly apply pressure until the pressure gauge reads 14.5 inches (48 kPa). Close off the air supply and wait 2 1 / 2 minutes.
  4.  
  5. Check the reading on the gauge. It should not have dropped below 13.5 inches (44 kPa).
  6.  
  7. Remove the filler cap. The pressure should drop to zero in a few seconds. If not, the vent line is clogged.
  8.  

Carbon Canister Purge Valve

See Figures 4 and 5

  1. Disconnect the rubber hose which runs between the manifold and canister at the T-connector.
  2.  
  3. Blow into the open end of the hose and listen for leaks.
  4.  
  5. If there are leaks, remove the top cover of the purge valve and check for a dislocated or cracked diaphragm. Replace the parts as necessary.
  6.  



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Fig. Fig. 4: Exploded view of carbon canister purge valve



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Fig. Fig. 5: Replacing the canister filter

Inspection and replacement can be accomplished without removing the canister.

  1. Inspect the filter on the bottom of the canister. If the filter is clogged, replace it.
  2.  

Flow Guide Valve

See Figure 6

  1. Disconnect the hoses to the valve.
  2.  
  3. Force low pressure air into the fuel tank vent connection. Air should flow from the crankcase side.
  4.  



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Fig. Fig. 6: Flow guide valve-1970-73 models only

  1. Force air into the air cleaner connection. Air should flow from the fuel tank and/or crankcase vent connection.
  2.  
  3. Force air into the crankcase vent line connection. There should be no leakage.
  4.  
  5. If the valve fails any of these tests, replace it.
  6.  

Fuel Check Valve

1976-78 MODELS
  1. Remove the valve from the vapor line.
  2.  
  3. Blow through the fuel tank side connector. Resistance should be felt and only a small flow of air should be felt at the engine side of the valve.
  4.  
  5. Blow through the engine side connector. Air should flow smoothly through the valve, emerging at the fuel tank side.
  6.  
  7. If the valve does not function correctly, replace it.
  8.  

1979-88 MODELS
  1. Remove the valve from the vapor line.
  2.  
  3. Suck air through the carbon canister connector. Air should flow only under high vacuum.
  4.  
  5. Suck air through the fuel tank side of the valve. Air should flow only under high vacuum.
  6.  
  7. Repeat Step 3 while closing off the carbon canister connector with your finger. Air should flow only under extremely high vacuum.
  8.  
  9. If the valve does not function correctly, replace it.
  10.  

 
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