Positive Crankcase Ventilation (PCV):

The Positive Crankcase Ventilation (PCV) system reduces blowby emissions from the engine. About 20% of the whole hydrocarbon (HC) emissions produced by a vehicle are blowby emissions from gases that get past the piston rings and enter the crankcase. The upper the mileage on the engine and also the greater the wear and tear on the piston rings and cylinders, the greater the blowby into the crankcase.

Before PCV was invented, blowby vapors were simply vented to the atmosphere through a “road draft tube” that ran from a vent hole in a very valve cover or valley cover down toward the bottom.

In 1961, the primary PCV systems appeared on California cars. The PCV system used an intake vacuum to siphon blowby vapors back to the manifold. This allowed the HC to be re-burned and eliminated blowby vapors as a source of pollution.

How to do Maintainance for PCV?

PCV Maintainance:

Because the PCV system is comparatively simple and requires minimal maintenance, it’s often overlooked. The common replacement interval for several PCV valves is 50,000 miles, yet many engines haven’t had the PCV valve replaced. Many late model owners’ manuals don’t even have a recommended replacement interval listed for the PCV valve. The manual may only suggest “inspecting” the system periodically.

On many 2002 and newer vehicles with OBD II, the OBD II system monitors the PCV system and checks the rate once during each drive cycle. But on older OBD II and OBD I systems, the PCV system isn’t monitored. So a controversy with the PCV system on a pre-2002 vehicle probably won’t activate the MIL (malfunction indicator lamp) or set a diagnostic trouble code (DTC).

PCV valves can last a protracted time, but they will eventually wear out or clog — especially if the vehicle owner neglects regular oil changes, and sludge builds up within the crankcase. The identical sludge and oil varnish that gums up the engine can even plug up the PCV valve.

PCV Replacement Tips:

When replacing a PCV valve, confirm the replacement valve is that the same because the original. External appearances will be misleading because valves that look identical on the skin are also calibrated differently inside. If the replacement valve doesn’t have the identical flow characteristics because of the original, it’s going to upset emissions and cause driveability problems.

The PCV hose that connects the PCV valve to the engine should even be replaced when the valve is modified. Use a hose that’s approved for PCV use only.

NOTE:

Can’t find your PCV valve? Some engines don’t have a PCV valve but use a crankcase ventilating system with a set orifice oil/vapor separator. The separator functions similarly to a PCV valve, but there’s no movable pintle or spring inside. The separator is just a little box with some baffles inside and a calibrated hole that permits the intake vacuum to tug the blowby vapors back to the manifold. Sort of a PCV valve, the separator can plug up with varnish and sludge, causing driveability and emissions problems.

How to Check PCV Valve?

PCV Valve Check:

There are many ways to test a PCV valve:

1. Remove the valve and shake it. If it rattles, it means the pintle inside isn’t stuck, and also the valve should flow air. But there are not any thanks to knowing if the spring is weak or broken, or if a buildup of varnish and deposits inside the valve is restricting flow.

2. Check for vacuum by holding your finger over the top of the valve while the engine is idling. This test tells you if the vacuum is reaching the valve, but not if the valve is flowing properly. If you do not feel a vacuum, it means the valve or hose is plugged and desires to get replaced.

3. Use a flow tester to test the performance of the valve. This method is the best because it tests both vacuum and airflow.

The volume of air that’s pulled from the crankcase by the PCV system is vital because it takes a specific amount of airflow to get rid of the blowby vapors and moisture. This prevents moisture contamination of the oil and therefore the formation of sludge within the crankcase. However, an excessive amount of airflow can upset the air/fuel mixture within the engine. It can even increase oil consumption.

What are Common Problems with PCV?

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.

How PCV Flow Changes With Engine Speed & Load?

PCV Flow Change:

The flow of a PCV valve is calibrated for a selected engine application. For the system to function normally, therefore, the PCV valve must adjust the flow as operating conditions change.

Engine OFF:

When the engine is off, the spring inside the valve pushes the pintle shut to seal the crankcase and stop the escape of any residual vapors into the atmosphere.

Engine ON:

When the engine starts, the vacuum within the manifold pulls on the pintle and sucks the PCV valve open. The pintle is pulled up against the spring and moves to its highest position. But the tapered shape of the pintle doesn’t allow maximum flow during this position. Instead, it restricts flow therefore the engine will idle smoothly.

Deceleration:

The same thing happens during deceleration when the intake vacuum is high. The pintle is pulled all the high to scale backflow and minimizes the effect of blowby on diesel emissions.

Engine Cruising:

When the engine is cruising under light load and at part throttle, there’s less intake vacuum and fewer pull on the pintle. this permits the pintle to slip down to a mid-range position and permit more airflow.

Acceleration:

Under high load or hard acceleration conditions, intake vacuum drops, even more, allowing the spring inside the PCV valve to push the pintle valve even lower to its maximum flow position. If blowby pressure builds up faster than the PCV system can handle it, the surplus pressure flows back through the breather hose to the air filter and is sucked into the engine and burned.

Engine Backfire:

In the event of an engine backfire, the sudden rise in pressure inside the manifold blows back through the PCV hose and slams the pintle shut. This prevents the flame from traveling back through the PCV valve and possibly igniting fuel vapors inside the crankcase.

How Does the PCV System Work?

PCV System Working:

The major component within the PCV system is that the PCV valve, an easy spring-loaded valve with a sliding pintle inside. The pintle is tapered sort of a bullet so it’ll increase or decrease airflow betting on its position inside the valve housing. The movement of the pintle up and down changes the orifice opening to manage the degree of air passing through the PCV valve. The PCV valve is usually located in an exceeding valve cover or the intake valley and frequently fits into a rubber grommet. The placement of the valve allows it to drag vapors from inside the engine without sucking oil from the crankcase (baffles inside the valve cover or valley cover deflect and help separate droplets of oil from the blowby vapors). A hose connects the highest of the PCV valve to a vacuum port on the throttle body, carburetor, or manifold. This enables the vapors to be siphoned directly into the engine without gumming up the throttle body or carburetor. Because the PCV system pulls air and blowby gases into the manifold, it’s the identical effect on the air/fuel mixture as a vacuum leak. This is often compensated for by the calibration of the carburetor or mechanical system. Consequently, the PCV system has no net effect on fuel economy, emissions, or engine performance — provided everything is functioning correctly.  

WARNING:

Removing or disconnecting the PCV system in a shot to enhance engine performance gains nothing, and is illegitimate. EPA rules prohibit tampering with any emission control device. Disabling or disconnecting the PCV system may allow moisture to accumulate within the crankcase, which is able to reduce oil life and promote the formation of engine-damaging sludge.

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