GM Full-Size Trucks 1980-1987 Repair Guide

PCV Valve



The PCV valve is located on top of a valve cover. Its function is to purge the crankcase of harmful vapors through a system using engine vacuum to draw fresh air through the crankcase. The fresh air is supplied through a crankcase breather that is located either in the air cleaner assembly or mounted to the opposite valve cover from where the PCV valve is located. The system reburns crankcase vapors, rather than exhausting them. Proper operation of the PCV valve depends on a sealed engine. If the oil begins to form sludge, which will be obvious as it is drained, and the PCV system is functioning properly, check the engine for possible causes.

Engine operating conditions that would indicate a malfunctioning PCV system are rough idle, oil present in the air cleaner, oil leaks or excessive oil sludging.

To check:

The PCV valve for proper operation, remove it from its rubber grommet on top of the valve cover and shake it. If it rattles, it is functioning; if not, replace it. In any event, it should be replaced at the recommended interval whether it rattles or not. Check the PCV hoses for breaks or restrictions. If necessary, the hoses should also be replaced. The plastic T-fittings used in this system break easily, so be careful.

See Figures 1, 2 and 3

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Fig. Fig. 1: If the crankcase breather is mounted inside the air cleaner assembly a hose will connect it to the valve cover

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Fig. Fig. 2: To free the crankcase breather, remove the C-clip from breather neck on the outside of the air cleaner assembly

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Fig. Fig. 3: PCV locations. Inline six valve also in valve cover

To replace the PCV valve:
  1. Pull the valve, with the hose still attached to the valve, from the rubber grommet in the rocker cover.
  3. Use a pair of pliers to release the hose clamp, remove the PCV valve from the hose.
  5. Install the new valve into the hose, slide the clamp into position, and install the valve into the rubber grommet.