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Can a Bad PCV Valve Cause an Engine to Smoke? (Explained)

PCV valves are an integral part of every engine. Their purpose is to regulate the amount of air and oil that enters and leaves the engine. They can malfunction if they are not working properly. Rather than drawing combustion gasses into the engine, the valve lets them escape. 

This guide will help you locate the cause of smoke coming from your PCV valve if you suspect that it is causing it.

Can A Bad PCV Valve Cause an Engine to Smoke?

A faulty PCV valve can result in your engine smoking. Most commonly, the cause of this problem is a buildup of carbon on the valves. Consequently, the valve can stick open, allowing air to enter into the engine and causing it to smoke. A replacement valve is the best solution. 

When the PCV valve in your car is not working properly, it can cause smoke. The valve allows air to escape from the engine while it is running, reducing the amount of oxygen available for combustion. If this happens, the engine will overheat and eventually fail.

Black smoke:

When PVC degrades and becomes brittle, it can cause engines to produce black smoke. Therefore, it is susceptible to breaking when subjected to stress, such as when the engine is under heavy load or when the temperature is high. 

When this happens, plastic fragments can fly out of the pipe and cause a fire or smoke to break out. Regularly inspect your PVC for signs of deterioration, and if any problems are noted, replace it right away.

White smoke:

When your PVC is bad, it can cause white smoke. This will depend on both the type of plastic used in its manufacture and the quality of the piping process used to manufacture it. 

Whenever you notice any problems with the interior components, such as heater core tubes, AC hoses, and dash panels, your pipe might be deteriorating. The anodization process is also suitable for other situations, such as water damage or acid leakage. 

PVC anodization alters and hardens PVC coatings.

Will a bad PCV valve cause the engine to burn oil? Can a bad PCV valve cause a misfire?

A bad PCV valve can cause the engine to burn oil. You may notice a burning scent coming from under the hood, which is caused by burnt oil. The engine must be fitted with the wrong components, such as a bad PCV valve or insufficient oil, for this to occur. 

By having a bad PCV valve, air and fuel can escape from the engine, which can result in oil burning. If the oil is not changed regularly or becomes contaminated with dirt or particulate matter, this could pose a serious fire risk.

A bad PCV valve can cause a misfire. As a PCV valve controls oil pressure, it can easily malfunction and cause electrical current problems in an engine. 

When this occurs, you may notice misfiring due to an overheated thermostat or block. Most manufacturers state that their products should not need replacing. 

However, when they are installed improperly with a cracked PVC coating, excessive temperature changes result. Repairing these valves is simply not worth the expense.

What happens when a PCV valve goes bad?

The following scenario occur when a PCV valve goes bad –

There will be smoke:

Whenever a PCV valve fails loudly, white smoke will come out of the exhaust. As well, if there is a faulty valve causing leaks, you should have a puddle of oil next to your car on black grass, leaves, or even dry grass. 

In addition to increased backfiring and blurry gauges, you might also experience problems with idle speed. Eventually, the engine may fail.


Misfiring and fuel odor can also be a result of a bad PCV valve since as time goes on, you will notice a noticeable decrease in throttle response. There is even a possibility that it will burn oil when idling if it is faulty. 

You should find the same puddle of oily exhaust next to your car at freeway speeds with a similar backfiring sound.

There will be no performance gain:

There will be no performance gain from increasing mileage or fuel economy if the plug is damaged. You may also need to check your oil and filter levels if this happens consistently over a long period. 

During acceleration, for example, you might notice that the engine pulls to one side and it seems off at times.

Fuel Issues:

The abnormal wear in the engine could create an even worse problem with fuel or oil consumption. When using this defective unit, many people report higher fuel and/or oil consumption on their Miata. 

You should always replace your car if you notice any strange things happening to it.

How do I know if my PCV valve is bad?

The following symptoms will indicate that your PCV valve has gone bad –

Differences in the oil filter:

Check for the difference in your oil filter. It is important to recognize any major changes in weird readings, such as a 1.3 reading which indicates it is very low quality or even signs of no oil present at all. 

You may have smelt fuel after driving through a city or town where the air conditioner blows through motors a lot.

Faulty sealing:

There’s a good chance that it has been damaged as well, particularly if the residue from it has been around your oil pan. 

These issues can occur as a result of failed seal replacements or aftermarket brands taking over despite faulty sealing due to blades that only last a few months on these units.


Look at where the intake manifold ground wire/shield enters the engine. Keep an eye out for rigidity in its construction at all times. The factory-fitted one of your Miatas is cheap-looking and prone to warping if flexed while running. 

If you notice any of these signs, it may be time for a new valve.

Increasing fuel consumption:

A faulty PCV valve will allow oil and gasoline vapors to escape from your engine, causing it to consume more fuel. As well as causing metal pieces to lodge in the mechanism, a failed PCV valve can cause an engine fire. 

You should service your car as soon as possible if you notice any of these signs.

How to fix a bad PCV valve?

It is possible to take care of a bad PCV valve on your own. The following steps will help you do that.

Warm up the engine:

Reducing the motor’s temperature when removing the valve should prevent any damage. Drain your car’s oil with a pressure wrench after shutting off the engine. 

Remove the four clamps on top of both valves with a new Phillips-head screwdriver tip; usually, these are marked K2 or c5/c4 on Miatas.

Be aware of what you are doing:

The first thing you should do is examine your valve and see if you can pinpoint the problem. In some cases, it is as simple as replacing one or two parts, while in other cases it may require more work. 

You may need to consult a mechanic or an online resource if you are unsure how the part should be replaced.

Taking the valves apart and removing them:

After identifying the problem area, disconnect both valves from their hoses by removing the screws that hold them in place. Pull them out of the ports by gently pulling them over when they are free.

Inspection and cleaning:

You should now clean both valves and inspect them for debris or damage. You should also replace any damaged gaskets or seals. Replace the valves by putting new screws into their ports and tightening them snugly. Oil the screws afterward to prevent corrosion.


Reinstall the valves into their ports and replace the screws. Be careful not to overtighten these screws as this could damage the valves. Check the engine compartment for leaks or gasps after starting your car.

Replacing the damaged part:

Purchasing new parts that need to be replaced at this time is a good idea. For removing or installing them into their respective ports in your valve train, follow your tuner’s instructions and use the tools he or she suggests. 

Put everything back together as before and test drive it! Look at your car repair manual if something doesn’t seem right to determine if a more serious problem needs to be addressed or what might be causing it.

Final Thought

You may notice smoke coming from your car’s exhaust if the PCV valve appears to be malfunctioning. You will need to take your car to a mechanic to check this. You can also replace the PCV valve if it is damaged. In most cases, this will resolve the issue and prevent your engine from smoking.