PCV Valve: How Does It Work, Failure Signs, How To Test It

Knowing how the PCV valve actually works, is the first step in diagnosing a bad or failing one.

When your engine is running, thousands of powerful explosions take place, to release the fuel energy. But, also produce highly toxic and harmful gases.

So, this simple emission control system, uses engine vacuum to pull blow-by gases, out of the crankcase. Then, pushes them down the intake manifold, and back into the combustion chambers, where they are reburned.

So, in 1961, the PCV valve system was introduced, to deal with this problem.

First, after each combustion process the exhaust valve, routes these gases into the exhaust system. Then, the catalytic converter turns them into much less toxic fumes, before releasing them into the atmosphere.

Still, a small amount of the gases in the combustion chambers, find their way into the crankcase. Because, of pressure leakage, between the piston rings and the cylinder wall.

So, if left on their own, these vapors and fumes, will play havoc with your engine. Because, blow-by gases contain, hydrocarbons (unburned fuel), carbon monoxide (partially burned fuel), particles, water, sulfur, and acid.

Also, together, these substances will corrode any engine metal component they touch. And, will dilute engine oil, build up harmful sludge that accelerates parts wear, and plug small passages and hoses.

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Signs Of A Failing PCV Valve

You need to know how important the PCV system is, to the well being of your engine. Do you understand how a failed PCV valve or any part of this system, disrupts engine performance and internal components.

So, a failed PCV valve or related component, can produce a number of symptoms. For example, if the valve gets stuck in the closed position or clogs. Then, you’ll notice one or more of these symptoms:

• Increase, in internal engine pressure.
• Failure of one or more, oil seals or gaskets.
• Engine oil leaks.
• Moisture and sludge buildup, inside the engine.
• Engine surges and possibly black smoke.

But, if the PCV valve gets stuck open, or a system hose gets disconnected or ruptured, producing a vacuum leak. Then, you’ll notice one or more of these symptoms:

• Engine misfires, at idle.
• Lean “air fuel” mixture.
• Presence of engine oil, in PCV valve or hose.
• Increased, oil consumption.
• Hard, engine start.
• Rough, engine idle.

In addition, a PCV valve stuck open, can trigger the “check engine” light, due to increased air flow.

However, a diagnostic computer, may point to a Mass Air Flow (MAF) or Oxygen (O2) Sensor failure instead. Consequently, making it harder for you to detect, the real source of the problem.

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PCV Valve Testing

Unfortunately, many car manufacturers are not strict, about PCV system maintenance. As a result, some suggest servicing the system, every 20,000 or 50,000 miles. However, a more frequent system inspection, helps prevent costly repairs and keep the engine running smoothly.

So, to start checking the PCV system in your vehicle, first locate the PCV valve and its related components.

Also, keep in mind that some new models, don’t have a PCV valve at all. Instead, you’ll find a simple vacuum hose, going from the valve cover to an air inlet duct. Others may have a simple restrictor in place. Still, you can check the restrictor, hoses and other components.

So, if you are not familiar with, the PCV system in your vehicle, or can’t find the valve. Then, buy the service manual for your particular vehicle make and model, from a local auto parts store.

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Luckily, It Doesn’t Take Much To Check The System:

1. Check PCV system parts. Rubber components like grommets, O-rings, and hoses swell and turn hard and brittle, after constant exposure to high temperatures. They begin to leak. Replace one or more of these components, as necessary.
2. Carefully disconnect the valve and any system hoses, and visually inspect them. If you find the hoses filled with slime, clean them with solvent or lacquer thinner, and replace the valve. Or, simply replace those components, along with the PCV valve.
3. Many engine models use a simple, cheap valve. As a result, many car owners just replace it, every service interval. Other valves incorporate heating elements and cost more. Regardless of the type of PCV valve your engine uses, always buy a quality brand valve. Because, it’s more likely to have a more precise calibration, for your specific engine model.
4. On some engines, you’ll find a mesh filter, underneath the valve. Some car manufacturers recommend, replacing the filter, every 30,000 miles or so.
5. Most vehicles come with a valve, that is nothing more than, a “spring loaded” device. Once you remove the valve, shake it with your hand. You’ll hear a rattle. If you don’t, it is time to replace the valve.