What are Common Problems with PCV?

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Common PCV Problems:

The most common problem that afflicts PCV systems is a plugged up PCV valve. An accumulation of fuel and oil varnish deposits and/or sludge inside the valve can restrict or perhaps block the flow of vapors through the valve. A restricted or plugged PCV valve cannot pull moisture and blowby vapors out of the crankcase. This may cause engine-damaging sludge to create, and a backup of pressure that will force oil to leak past gaskets and seals. The loss of airflow through the valve can even cause the air/fuel mixture to run richer than normal, increasing fuel consumption and emissions. The identical thing can happen if the pintle inside the PCV valve sticks shut.


Stick Open:

If the pintle inside the PCV valve sticks open, or the spring breaks, the PCV valve may flow an excessive amount of air and lean out the idle mixture. This might cause a rough idle, hard starting, and/or lean misfire (which increases emissions and wastes fuel). The identical thing can happen if the hose that connects the valve to the throttle body, carburetor, or manifold pulls loose, cracks, or leaks. A loose or leaky hose allows “un-metered” air to enter the engine and upset the fuel mixture, especially at idle where the idle mixture is most sensitive to vacuum leaks.


Late Model Vehicles:

On late-model vehicles with computerized engine controls, the engine management system will detect any changes within the air/fuel mixture and compensate by increasing or decreasing short term and long-run fuel trim (STFT and LTFT). Small corrections cause no problems, but large corrections (more than 10 to fifteen points negative or positive) will typically set a lean or rich DTC and switch on the MIL.


Incorrect PCV:

Problems may occur if someone installs the incorrect PCV valve for the applying. As we said earlier, the rate of the PCV valve is calibrated for a particular engine application. Two valves that appear to be identical on the surface (same diameter and hose fittings) may have different pintle valves and comes inside, giving them very different flow rates. A PCV valve that flows an excessive amount of air will lean the air/fuel mixture, while one that flows deficient will richen the mixture and increase the chance of sludge buildup within the crankcase.

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