GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Cooling 🢒 Crankcase Ventilation System Inspection/Diagnosis

The compressed combustion gas which escapes past the piston rings into the crankcase is known as blowby gas. Blowby gas contains large amounts of carbon monoxide (CO) and hydrocarbon (HC). The positive crankcase ventilation (PCV) system prevents the blowby gas from being emitted into the atmosphere. The PCV system routes crankcase blowby gas back into the intake system where it becomes part of the combustion process. The PCV system consists of the following components:

    • The PCV valve
    • The crankcase vent or air inlet tube
    • The air inlet filter or separator, if used
    • Any hoses or couplers

Operation
Object Number: 720720 Size: SH

The primary control of engine crankcase blowby gas is the PCV valve (1). The PCV valve meters the flow of blowby gas according to the manifold vacuum signal.

PCV Valve
Object Number: 56689 Size: SH
(1)Check Valve

In order to maintain idle quality, the PCV valve restricts the flow of blowby gas whenever intake manifold vacuum is high. Abnormally high crankcase pressure may cause the blowby gases to flow through the crankcase vent tube and into the air cleaner. The blowby gases are then drawn into the intake system and consumed in the normal combustion process. The relationship between the flow of blowby gas and engine manifold vacuum is charted in the following table:

PCV Valve Operation

Manifold Vacuum

PCV Valve Opening

Blowby Gas Flow

Low

Large

High

High

Small

Low

Results Of Incorrect Operation

A plugged valve or hose may cause any of the following conditions:

    • A rough engine idle
    • Engine stalling or low engine idle speed
    • High engine crankcase pressure
    • Engine oil leaks
    • Engine oil in the air cleaner
    • Oil sludge in the engine
    • Engine oil consumption
    • Excessive exhaust emissions

A leaking valve or hose may cause any of the following conditions:

    • A rough engine idle
    • Engine stalling
    • High engine idle speed
    • Incorrect engine crankcase pressure
    • Excessive exhaust emissions

Notice: Operating an engine without an effective crankcase ventilation system may damage the engine. Replace the Positive Crankcase Ventilation (PCV) valve at regular intervals. Use the correct PCV valve for the engine and equipment type. Wrong or substandard parts may damage the engine components.

Use the following procedure to check the function of the PCV system.


    Object Number: 720720 Size: SH
  1. Start the engine.
  2. Run the engine at idle.
  3. Remove the PCV valve (1) and place your thumb over the end of the PCV valve to check for vacuum. If there is no vacuum at the PCV valve, check for a plugged intake manifold port, PCV valve, or vacuum hose. Replace or repair as necessary.
  4. Turn OFF the ignition.
  5. Remove the PCV valve.

    6. Object Number: 158669 Size: SH
  6. Shake the PCV valve while listening for the rattle of the needle inside. Replace the PCV valve if the valve does not rattle.
    7. •  Proper operation of the PCV system is dependent upon a sealed engine with a freely flowing breather tube.
       - Check that the PCV breather tube and pipe are not blocked.
       - Check that the coolant passages at the breather pipe are becoming hot after the engine runs a short time.
    • Repair as necessary.
    • Build up of oil sludge or oil dilution is an indication of a leak in the PCV system or crankcase.
       - Inspect all the hoses and clamps in the PCV system for signs of damage or deterioration.
       - Inspect the engine for external oil leaks.
    • Repair as necessary.
  7. Install the PCV valve to the PCV hose.
  8. Install the PCV valve and hose into the valve cover.