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Home >> GMC >> 1990 >> Forward Control 5.7 K, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Fuel Evaporation Control >> Checking PCV Valve Function
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Checking PCV Valve Function

  1. Remove PCV valve from rocker cover. Run engine at idle. Place thumb over open end of valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary.
  2. Turn engine off. Remove PCV valve. Shake valve and listen for rattle of check valve inside. If a clear rattle is not heard, replace PCV valve.
  3. Visually inspect valve for varnish or deposits which may make PCV valve operation sticky, restricted or cause incomplete seating of valve. Replace if necessary.
  4. An engine must be sealed for the PCV system to function as designed. If leakage, sludging or dilution of oil is noted and the PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
  5. An engine operating without any crankcase ventilation can be damaged so it is important to replace PCV valve and air cleaner breather at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.
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