How does PCV Valve Work? | What are the Symptoms of a bad PCV Valve?

PCV stands for Positive Crankcase Ventilation. A PCV valve is used to remove the exhaust gases from the engine crankcase. The Positive Crankcase Ventilation (PCV) valve recirculates the exhaust gases through the intake manifold to the combustion chamber. It plays a key role in engine performance, improving emissions and overall vehicle operation. Faulty PCV valves can reduce engine performance. This article mainly explains the bad PCV valve symptoms, its causes, and replacement cost.   

What is a PCV Valve?

The PCV valve expels undesirable exhaust gases from the crankcase and recirculates them through the intake manifold to the combustion chamber. These exhaust gases then burn in the combustion chamber instead of going into the environment through the exhaust system.  

PCV Valve

The PCV valve is a one-way valve that is connected to the crankcase. Exhaust gases leave the crankcase through this valve but can’t reenter the crankcase.

Fuel combustion in the engine creates exhaust gases that are expelled through the exhaust system. But some of that exhaust gases pass through the piston into the crankcase. When the exhaust gases enter the crankcase, they mix with the oil, creating a sludge that can corrode and clog engine passages and damage engine components.

However, the owners of the Evanston vehicles need to be aware that these gases may increase crankcase pressure when the engine operates at high RPM. The increase in the crankcase pressure may damage seals, blow gaskets and cause oil leaks.

The exhaust gases leaving the engine contain approximately 70 percent unburned fuel. These gases are expelled into the atmosphere through the crankcase.

PCV systems of your vehicle reduce dangerous emissions from vehicles.

Revving the engine up and running it at a higher speed will open the PCV valve wider, allowing more crankcase ventilation to be drawn in due to the higher speed and faster crankcase pressure accumulation.

The required maintenance of the PCV system is simple and economical. A damaged or dirty PCV system may cause serious engine damage for Evanston drivers.

How does a PCV Valve Work?

The Positive Crankcase Ventilation valve is a one-way check valve. It has a spring-loaded plunger that regulates the exhaust gas flow. One end of the valve connects to a hose that connects to the hood or intake duct, and the other end usually connects to the vacuum manifold. 

PCV Valve Working, Positive Crankcase Ventilation valve

As your vehicle engine is turned off, an internal spring in the PCV valve closes the plunger. When the engine is operating, the manifold vacuum pulls the plunger away to open it. An open PCV valve allows fresh air from the crankcase to go into the engine through the breather tube. The resultant scavenging action introduces exhaust gas to the PCV valve.

As the exhaust gas leaves the valve, it enters a rubber hose that is usually linked to the throttle body or intake manifold of your engine. After passing through the rubber hose, the exhaust gas enters the combustion chamber, where it is burned in the normal combustion progression.

However, the PCV valve does not always permit the same amount of exhaust gases to go into the combustion chamber. Therefore, the valve uses an internal plunger to control the exhaust gas flow as follows:

  • A higher vacuum in the manifold reduces the formation of exhaust gases. In such a condition, the vacuum jerks the plunger away from its seat, allowing exhaust gas to flow only through small holes in the plunger body.
  • When the vacuum reduces, and blowby increases, the plunger of your valve further moves off the seat until it reaches the extreme flow position. When the valve opens completely, the crankcase gases can freely enter the engine’s intake system.

Bad PCV Valve Symptoms

When the PCV valve goes bad, it produces one of the below-given symptoms:

  • Check Engine Light
  • Smoke from the Exhaust Pipe
  • Lean/Rich Mixture
  • High Idle RPM/Rough Idle
  • Rough Acceleration
  • Poor Oil Economy
  • Engine Misfiring
  • Contaminated filter
  • Engine Stalling
  • Unusual Engine Noises
  • Sludge Accumulation

1) Check Engine Light Illumination

The check engine light illumination is one of the first symptoms of a bad PCV valve. Whenever the check engine light comes on, an error code is stored in the powertrain control module (PCM).

check engine light illumination due to bad PCV valve

Take an OBD2 scanner to scan the trouble codes. Some old vehicle models with PCV valves don’t have an electronically controlled engine unit. Such models don’t show this symptom.

Read More: Causes of Check Engine Light Illumination

2) Smoke from the Exhaust Pipe

The black or white smoke from the exhaust pipe is one of the clear symptoms of a faulty or clogged PCV valve. When the hoses or valve goes bad, your crankcase forces the engine oil to burn in the engine combustion chamber. This causes a lot of blue or black smoke to come out of the tailpipe.

smoke from tailpipe due to bad PCV valve

If your PCV valve fails, then your air-fuel mixture becomes too lean or too rich, and your engine may produce symptoms such as white or black smoke from the exhaust pipe, depending on the nature of the engine mixture problem.

3) Lean/Rich Mixture

As we discussed, the PCV valves use to control the air flow between the crankcase and intake manifold. Therefore, a faulty PCV valve may lead to a rich or lean engine due to an improper fuel-air mixture.

Air Fuel Mixture

If the engine is running rich, you can easily observe bad PCV valve symptoms, the smell of gasoline in the smoke, or white smoke coming out from the exhaust pipe. A lean engine is usually very difficult to diagnose and can lead to engine misfires.

4) High Idle RPM/Rough Idle

Rough idling or higher engine RPM is one of the major symptoms of a faulty PCV valve. A PCV valve uses to regulate the flow of air between the intake manifold and the crankcase.

Rough Idle due to bad Positive Crankcase Ventilation valve

A damaged Positive Crankcase Ventilation valve may show similar signs as an intake leak and cause high idle RPM or other abnormal idle behavior such as engine stalling.

5) Rough Acceleration

If your Positive Crankcase Ventilation valve fails and the fuel doesn’t mix properly, you’ll feel the vehicle accelerate roughly at both low and high speeds.

acceleration problems

In the case of some vehicles, the vehicle doesn’t show the symptoms of a bad PCV valve at a higher speed than idle, but it depends on the valve design.

6) Poor Oil Economy 

A faulty PCV valve may lead to an oil leak and poor oil economy. In such conditions, oil can leak out of the gaskets and drip onto the garage floor. This is because extreme pressure can build up in the crankcase if the valve goes bad. In this situation, the oil will then be forced out of the gaskets as there is no other path to relieve the pressure.

Poor oil economy

An oil leak may cause the car to burn oil and cause oil to leak from under the car. If you notice any of these symptoms, immediately contact a professional to replace the PCV valve.

7) Engine Misfiring

The engine misfiring is also a sign of a faulty PCV valve. Most commonly, the misfire occurs due to a rich/lean fuel-air mixture that can cause the engine to idle or stall while driving. Too much fuel or too much air will cause your car’s engine to misfire and slow down.

Engine Misfiring

8) Contaminated Filter

When the PCV valve begins to fail, your vehicle filter, known as the breather element, can become contaminated with oils and hydrocarbons. This is because the pressure in the crankcase increases, and water vapor starts to flow through the breather element. When the water enters the breather element, it can mix with gas, causing deposits and leading to poor fuel economy.

The best method to inspect the breather element is to physically check the filter for debris. Another method is to calculate the fuel consumption of the car. If it begins to drop for no apparent reason, the Positive Crankcase Ventilation valve may be defective.

9) Engine Stalling

A faulty PCV valve can cause the piston to remain open. This causes an unusual amount of air to enter the combustion cylinder.

This creates a leaner air-fuel mixture because the engine cylinder has more air than fuel. As a result, the engine may stall or run poorly at idle.  

engine Stalling due to bad PCV valve

10) Unusual Engine Noises

A faulty Positive Crankcase Ventilation valve can cause the engine to make strange noises. Grunts and hisses can be heard from behind the hood.

Such noises usually produce due to leakage of the air through the valve or the holes in the valve hose. Random noises are almost always an indication that something is wrong, so keep an eye out for knocking and other unexpected engine noises.

11) Sludge Accumulation

If you don’t check a blocked PCV valve, the crankcase oil will begin to collect moisture and eventually form sludge in the engine.

How To Replace the PCV Valve

The on-time replacement of a bad PCV valve is very important to ensure the efficient working of the engine. Follow the below-given steps to replace the PCV valve:

  1. Fir of all, you need to find the PCV valve. After locating the valve, loose its hose clamp or remove the small L-shaped cap from the end of the valve.
  2. Remove the valve. Some types of valves are tightened with rubber grommets that can be easily detached.
  3. Visually inspect the grommets/clamps and hoses. Remove the hose and blow it out. Replace hoses if they are dry, spongy, mushy, stiff, soft, or blocked with mud.
  4. Screw on and reinstall the valve. If your valve replacement needs screwing in, do so by hand to avoid stripping the hood threads.
  5. Repair the hose connection to the PCV valve. Start the engine and check for leaks around the valve.

PCV Valve Replacement Cost

The replacement cost of the PCV valve varies according to the vehicle model, labor cost, and your living area.

The average replacement cost of the PCV valve is from $40 to $260. In this cost, the cost of the labor is from $25 to $200 while the labor cost is from $15 to $60.

FAQ Section

What is the function of the PCV valve?

The Positive Crankcase Ventilation valve controls pressure to remove exhaust gases from the crankcase. It reduces the effects of crankcase vacuum by releasing exhaust gases. This prevents damage to the engine seals (which can explode if over-pressurized).

Where is the PCV valve located?

The PCV valve is usually located in the valve cover on top of the engine. However, in the case of some vehicles, it may be installed on the hose between the air intake filter and the rocker cover.

You can find the PCV valve by following the hose on top of your car’s engine. Some vehicles also contain an integrated PCV valve along with a valve cover.

Can you clean the PCV valve?

Yes, you can clean the PCV valve if it is blocked. However, in many cases, the spring mechanism inside the valve goes bad with time. PCV valves are usually very inexpensive and can be cleaned easily. It is recommended to replace it to avoid issues in the future.

Is the PCV valve necessary?

The PCV valve ensures the removal of waste gases from the crankcase. In this way, it prevents the engine from many issues, such as misfiring and engine stalling. However, if your vehicle doesn’t have the PCV valves, the crankcase pressure can be too low at idle, or the crankcase pressure can be too high when the turbo is ramped up.

Can you drive with a bad PCV valve?

Yes, you can drive with a bad PCV valve, but it is not recommended. A bad valve may generate different drivability issues, such as poor acceleration, misfiring, or poor fuel economy.

What happens when a PCV valve fails?

As the PCV valve fails, it produces one or more of the below-given symptoms:

  • Check engine light
  • Sludge accumulation
  • Engine stalling
  • Smoke from the exhaust pipe
  • Lean/Rich mixture
  • High idle RPM/rough idle
  • Unusual engine noises
  • Rough acceleration
  • Poor oil economy 
  • Contaminated filter
  • Engine misfiring

How often should a PCV valve last?

There is no time to replace the PCV valves. The life of the PCV valve should be as long as possible. Ideally, the valve should be checked after every major service. As a general rule of thumb, we recommend replacing the valve every 30,000 miles to 50,000 miles.

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