Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

Crankcase Ventilation System

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OPERATION



See Figures 1, 2, 3, 4, 5, 6, 7, 8 and 9



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Fig. Fig. 1: Check the PCV valve for vacuum at idle



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Fig. Fig. 2: PCV control system components-E15, E15ET, E16S and E16i engines



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Fig. Fig. 3: PCV control system components-SR20DE engine



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Fig. Fig. 4: PCV control system components-GA16i engine



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Fig. Fig. 5: PCV valve operation



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Fig. Fig. 6: With the PCV valve removed, check that a strong vacuum is felt from the valve at idle



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Fig. Fig. 7: Blow air through the ventilation hose, ensuring that it is clear



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Fig. Fig. 8: Oil separator location-CA18DE engine shown, others with external separator similar



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Fig. Fig. 9: PCV control system components-GA16DE engine

When the engine is running, a small portion of the gases which are formed in the combustion chamber during combustion, leak by the piston rings and enter the crankcase. Since these gases are under pressure they tend to escape from the crankcase and enter into the atmosphere. If these gases were allowed to remain in the crankcase for any length of time, they would contaminate the engine oil and cause sludge to build up. If the gases are allowed to escape into the atmosphere, they would pollute the air, for they contain unburned hydrocarbons. The crankcase emission control equipment recycles these gases back into the engine combustion chamber where they are burned.

Crankcase gases are recycled in the following manner: when the engine is running, clean filtered air (from the carburetor air filter) is drawn into the crankcase or the rocker cover, through a hose. As the air passes through the crankcase it mixes with combustion gases, then carries them (out of the crankcase) through the PCV valve and into the intake manifold. After they enter the intake manifold they are drawn into the combustion chamber and burned.

The most critical component in the system is the PCV valve. This vacuum controlled valve regulates the amount of gases which are recycled into the combustion chamber. At low engine speeds, the valve is partially closed, limiting the flow of gases into the intake manifold. At increased engine speeds, the valve opens to admit greater quantities of the gases into the intake manifold. If the valve should become blocked or plugged, the gases will be prevented from escaping from the crankcase by the normal route. Since these gases are under pressure, they will find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket, it also creates an oil leak. Besides causing oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period of time, promoting the formation of sludge in the engine.

The crankcase emission control equipment consists of a positive crankcase ventilation valve (PCV), an oil filler cap (sealed) and hoses (connected to the equipment). The CA16DE, CA18DE and SR20DE engines use an external oil separator (in the PCV line) to keep excess oil in the crankcase, away from the PCV valve.

TESTING



To check the PCV system, inspect the PCV valve, the air filter(s), the hoses, the connections and the oil separator (SR20DE, CA16DE and CA18DE engines); check for leaks, plugged valve(s) and/or filters, then replace or tighten, as necessary.

To check the hoses, use compressed air to free them or replace them. If the air filters are dirty, replace them.

Test the PCV valve as follows:

  1. Pull the PCV valve out of the cylinder head with the engine running. Place a finger over the valve inlet. A strong vacuum should be present.
  2.  
  3. Remove the valve from the hose. Lightly shake the valve. The plunger should be audible as it rattles inside.
  4.  

If the valve fails to function as outlined, replace it with a new one; DO NOT attempt to clean or adjust it.

REMOVAL & INSTALLATION



PCV Valve
  1. Disconnect the valve from the PCV hose.
  2.  
  3. Unscrew the PCV valve out of the rocker cover.
  4.  
  5. Screw the valve into the rocker cover and carefully tighten the valve.
  6.  


WARNING
Do not overtighten the valve. The valve will seal with a light amount of torque.

  1. Connect the vacuum hose to the valve and secure with the retaining clamp.
  2.  

PCV Filter

Replace the PCV filter inside the air cleaner, at the recommended maintenance intervals, or more frequently if operating in dusty or smoggy conditions.

To replace the PCV filter, remove the air cleaner cover and remove the filter cartridge.

 
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