GM Lumina/Grand Prix/Cutlass Supreme/Regal 1988-1996

Crankcase Ventilation System



See Figures 1, 2 and 3

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Fig. Fig. 1: Cross-section of a PCV or CV valve

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Fig. Fig. 2: The PCV system circulates crankcase vapors into the intake manifold for burning-2.5L engine

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Fig. Fig. 3: Schematic of the PCV system-1996 3.1L engine shown

The Positive Crankcase Ventilation (PCV) or Crankcase Ventilation (CV) system is used on all vehicles to evacuate the crankcase vapors. Fresh air from the air cleaner or intake duct is supplied to the crankcase, mixed with blow-by gases and then passed through a Positive Crankcase Ventilation (PCV) valve into the intake manifold or the air plenum.

When manifold vacuum is high, such as at idle, the orifice or valve restricts the flow of blow-by gases allowed into the manifold. If abnormal operating conditions occur, the system will allow excessive blow-by gases to back flow through the hose into the air cleaner. These blow-by gases will then be mixed with the intake air in the air cleaner instead of in the manifold. The air cleaner has a small filter attached to the inside wall that connects to the breather hose to trap impurities flowing in either direction.

A plugged PCV valve, orifice or hose may cause rough idle, stalling or slow idle speed, oil leaks, oil in the air cleaner or sludge in the engine. A leak could cause rough idle, stalling or high idle speed. The condition of the grommets in the valve cover will also affect system and engine performance.

Other than checking and replacing the PCV valve and associated hoses, there is no service required. Engine operating conditions that would direct suspicion to the PCV system are rough idle, oil present in the air cleaner, oil leaks and excessive oil sludging or dilution. If any of the above conditions exist, remove the PCV valve and shake it. A clicking sound indicates that the valve is free. If no clicking sound is heard, replace the valve. Inspect the PCV breather in the air cleaner. Replace the breather if it is so dirty that it will not allow gases to pass through. Check all the PCV hoses for condition and tight connections. Replace any hoses that have deteriorated.


See Figure 4

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Fig. Fig. 4: Check the PCV valve for vacuum at idle

PCV Valve
  1. Start the engine.
  3. With the engine at normal operating temperature, run at idle.
  5. Remove the PCV valve or orifice from the grommet in the valve cover and place thumb over the end to check if vacuum is present. If vacuum is not present, check for plugged hoses or manifold port. Repair or replace as necessary.
  7. Stop the engine and remove the valve. Shake the valve and listen for the rattle of the check valve needle. If there is no rattle heard when the valve is shaken, replace the valve.

PCV System
  1. Check to make sure the engine has the correct PCV valve or bleed orifice.
  3. Start the engine and bring to normal operating temperature.
  5. Block OFF the PCV system fresh air intake passage.
  7. Remove the engine oil dipstick and install a vacuum gauge on the dipstick tube.
  9. Run the engine at 1500 rpm for 30 seconds then read the vacuum gauge with the engine at 1500 rpm.

    If vacuum is present, the PCV system is functioning properly.
    If there is no vacuum, the engine may not be sealed and/or is drawing in outside air. Check the grommets and valve cover or oil pan gasket for leaks.
    If the vacuum gauge registers a pressure or the vacuum gauge is pushed out of the dipstick tube, check for the correct PCV valve or bleed orifice, a plugged hose or excessive engine blow-by.



Removal and installation procedures of the PCV or CV valve is located in Routine Maintenance of this repair guide.