GM Cadillac 1967-1989 Repair Guide

Positive Crankcase Ventilation (PCV Valve)

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See Figures 1, 2, 3, 4, 5 and 6

All gasoline engines covered in this guide are equipped with a closed crankcase emission control system (see Emission Controls ) featuring a vacuum-operated Positive Crankcase Ventilation valve (PCV). A faulty PCV valve or clogged hoses to and from the valve can cause a rough idle, oil leaks, or excessive oil sludging. Check the system at least once a year and replace the valve at least every 30 months or 30,000 miles. A general test is to remove the PCV valve from the valve cover and shake it. If a rattle is heard, the valve is usually OK.

A more positive test is:
  1. Remove the PCV valve from the rocker arm cover or intake manifold.
  2.  
  3. Connect a tachometer to the engine and run the engine at idle.
  4.  
  5. Check the tachometer reading, then place your thumb over the end of the valve. You should feel a suction.
  6.  
  7. Check the tachometer again. The engine speed should have dropped at least 50 rpm. It should return to a normal idle when you remove your thumb from the end of the valve.
  8.  
  9. If the engine does not change speed or if the change is less than 50 rpm, the hose is clogged or the valve defective. Check the hose first-if it is not clogged, replace the PCV valve. Test the new valve in the same way.
  10.  



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Fig. Fig. 1: Checking the PCV valve for vacuum



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Fig. Fig. 2: Common PCV system flow



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Fig. Fig. 3: PCV valve and hose between the rocker cover and throttle body - 1986-89 Eldorado and Seville



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Fig. Fig. 4: Common PCV valve and crankcase breather - carbureted engines



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Fig. Fig. 5: PCV filter at the air cleaner - 1986-89 Eldorado and Seville



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Fig. Fig. 6: Common PCV location in the valve cover

 
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