Isuzu Cars and Trucks 1981-1991

Crankcase Ventilation System

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OPERATION
Gasoline

The carbureted gasoline 4-cyl. engines do not use a PCV valve. In place of the valve is a regulating orifice in the intake manifold. Blow-by gases are drawn through the regulating orifice into the intake manifold for reburning. During wide open throttle, the engine vacuum is not sufficient to draw enough vapor through the manifold, allowing part to be drawn into the air cleaner via the rear end of the rocker arm cover.

The fuel injected gasoline 4-cyl. and V6 engines use a PCV valve. The PCV valve meters the flow at a rate depending upon the manifold vacuum. If the manifold vacuum is high, the PCV restricts the flow to the intake manifold. If abnormal, operating conditions occur, excessive amounts of internal exhaust gases back flow through the crankcase vent tube into the air filter to be burned by normal combustion.

The crankcase ventilation system (PCV) must be operating correctly to provide complete scavenging of the crankcase vapors. Fresh air is supplied to the crankcase from the air filter, mixed with the internal exhaust gases, passed through the PCV valve or orifice and into the intake manifold.

If the engine is idling roughly, a quick check of the PCV valve can be made. While the engine is idling, pull the PCV valve from the valve cover, place your thumb over the end of the PCV valve and check for vacuum. If no vacuum exists, check for a plugged PCV valve, manifold port, hoses or deteriorated hoses. Turn the engine "OFF", remove the PCV valve and shake it. Listen for the rattle of the check needle inside the valve. If it does not rattle, replace the valve.

The PCV system should be checked at every oil change and serviced every 30,000 miles.


NOTE
Never operate an engine without a PCV valve or a ventilation system, for it can become damaged.



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Fig. PCV system carbureted 4-cyl. gas engines do not use a valve. They use a regulating orifice located in the intake manifold



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Fig. PCV system 4-cylinder gas EFT 4ZE1 engine



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Fig. PCV system 6-cylinder engine

Diesel Engine

The crankcase ventilation system is a closed type, and is designed to force blow-by gas generated in the engine crankcase back into the intake manifold to return with the fresh air back into the combustion chamber.

When the engine is running at high speed, the high negative pressure from the intake manifold makes the diaphragm valve close, as a result, the blow-by gas passes through the regulating orifice. When the engine is running at low speed, the negative pressure from the intake manifold is so small that the cylinder head cover pressure makes the diaphragm valve open. As a result, the blow-by gas passes through both the regulating orifice and the diaphragm passage opened by the diaphragm valve.



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Fig. PCV system 4-cylinder diesel engine



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Fig. PCV system 4FB1 diesel engine (California)



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Fig. PCV system 4FB1 diesel engine (California)



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Fig. PCV system C223 diesel engine



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Fig. PCV system C223 Turbo diesel

SERVICE
PCV Valve

Check the diaphragm valve for damage and adhesion to the seating surface. Check the oil separator element for wear if any abnormal conditions are found, replace the PCV valve assembly.



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Fig. PCV valve operation 4FB1 diesel engine (California)

Check Valve

Using a vacuum pump, check the valve function. If the air flows in the wrong direction or if the valve is plugged, replace the check valve.



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Fig. Check valve 4FB1 (California) and C223 Turbo diesel

Hoses

Check the rubber hoses for deterioration and damage. Also check for proper routing. Refer to the vacuum diagrams at the end of this Section.

REMOVAL AND INSTALLATION

Label the PCV valve hoses before removing. Disconnect the hoses and remove the valve. Remove the valve cover and clean the oil separator and diaphragm. Clean all components with solvent and reinstall. Replace any defective components.

 
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