Toyota Celica/Supra 1971-1985 Repair Guide

Crankcase Ventilation System

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OPERATION



See Figures 1, 2, 3, 4 and 5



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Fig. Fig. 1: The PCV valve regulates flow according to engine operating conditions



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Fig. Fig. 2: PCV system flow on carbureted four cylinder engines



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Fig. Fig. 3: PCV system flow on SOHC fuel injected engines-except 22R-EC



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Fig. Fig. 4: PCV system flow on DOHC fuel injected engines



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Fig. Fig. 5: PCV system flow on 22R-EC engines

A closed, Positive Crankcase Ventilation (PCV) system is employed on all Celicas and Supras. This system cycles incompletely burned fuel which works its way past the piston rings back into the intake manifold for reburning with the air/fuel mixture. The oil filler cap is sealed and the air is drawn from the top of the crankcase into the intake manifold through a valve with a variable orifice (the 4M-E, 5M-E and 5M-GE engines have no valve, only an orifice).

This valve (commonly known as the PCV valve) regulates the flow of air into the manifold according to the amount of manifold vacuum. When the throttle plates are open fairly wide, the valve opens to maximize the flow. However, at idle speed, when manifold vacuum is at a maximum, the PCV valve throttles the flow in order not to unnecessarily affect the small volume of mixture passing into the engine.

During most driving conditions, manifold vacuum is high and all of the vapor from the crankcase, plus a small amount of excess air, is drawn into the manifold via the PCV valve. However, at full throttle, the increase in the volume of blow-by and the decrease in manifold vacuum make the flow via the PCV valve inadequate. Under these conditions, excess vapors are drawn into the air cleaner and pass into the engine.

TESTING



See Figures 6, 7 and 8



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Fig. Fig. 6: Blow air from the cylinder head side of the PCV valve, it should flow easily



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Fig. Fig. 7: Blow air from the intake manifold side, check that the air passes with difficulty



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Fig. Fig. 8: Leaks from any of these areas can cause the PCV system to malfunction

Inspect the PCV system hoses and connections at each tune-up and replace any deteriorated hoses. Check the PCV valve at every tune-up and replace it at 30,000 mile (48,000 km) intervals.

The PCV valve is easily checked with the engine running at normal idle speed (warmed up).

  1. Remove the PCV valve from the valve cover or intake manifold, but leave it connected to its hose.
  2.  
  3. Start the engine.
  4.  
  5. Place your thumb over the end of the valve to check for vacuum. If there is no vacuum, check for plugged hoses or ports. If these are open, the valve is faulty.
  6.  
  7. With the engine OFF , remove the valve completely. Shake it end-to-end, listening for the rattle of the needle inside the valve. If no rattle is heard, the needle is jammed (probably due to oil sludge) and the valve should be replaced.
  8.  


CAUTION
Don't blow directly into the valve; petroleum deposits within the valve can be harmful.

An engine without crankcase ventilation is quickly damaged. It is important to check the PCV at regular intervals. When replacing a PCV valve you must use the correct one for the engine. Many valves look alike on the outside, but have different mechanical values. Putting the incorrect valve on a vehicle can cause a great deal of driveability problems.

REMOVAL & INSTALLATION



  1. Pull the PCV valve from the valve cover or the intake manifold.
  2.  
  3. Remove the hose from the valve.
  4.  
  5. Check the valve for proper operation.
  6.  
  7. Inspect the rubber grommet the PCV valve fits into. If it is in any way deteriorated or oil soaked, replace it.
  8.  

To install:
  1. Insert a new valve into the hose.
  2.  
  3. Push the valve into the rubber grommet. Make sure the valve is firmly into place.
  4.  

 
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