Symptoms of Wrong Power Valve Briefly Explains Fails/Blows out

The value of the power valve- too small or too big, both is bad and in other words- wrong. How will you know that the power valve is wrong? Your vehicle will show some symptoms, obviously. 

symptoms of too low power valve

In this article, we are going to show you the symptoms so that you know the moment these symptoms arise, there is something wrong with the power valve. 

Symptoms of a wrong power valve (Explained)

What are the symptoms of a blown power valve? The incorrect size ratio of power valve, blown out power valve has the chance for poor fuel economy, reduce gas mileage, black smoke in the exhaust, dark or fouling spark plugs caps/wires.

We have already said this earlier. Neither too high nor too low of the value of the power valve is going to work properly for the engine. You will know about the wrong power valve by some common symptoms. These symptoms are quite similar to the symptoms of the blown power valve. Well, in both cases, you have to change the power valve. So, that is not an issue. Let’s head into the symptoms-

Symptoms that will arise if the value of the power valve is too low

does power valve affect idle
  • Backfires and popping: Whenever you are trying to accelerate, you see backfires in the engine. Well, if that happens, there is a big chance that the power valve is wrong. Especially the value of the power valve is too low in this case. You have to install a higher valued power valve to battle this situation. 
  • Poor acceleration: Leave the backfires. Even without the backfiring symptoms, the acceleration itself may become faulty. You will experience a very poor acceleration in this case. If something like this happens, you must check the power valve immediately. Chances are you have put a power valve of higher value. 
  • Too lean air/fuel mixture: Another thing you will notice if the value of the power valve becomes too low is that the air/fuel mixture will be too lean. We know how bad this thing is. Thus the advice is the moment you notice a lean mixture, take the necessary steps to resolve this issue. 

Symptoms that will arise if the value of the power valve is too high

  • Poor idling: The first thing you will notice if the power valve is wrong (value is too high) is the poor idling of your vehicle. Although rough idle happens for various other reasons, you want to check whether the power valve is okay or not. 
  • Spark plug residue: If the spark plug becomes contaminated with something like fuel, oil, or carbon, you should check the power valve. Sometimes, due to the too high value of the power valve, the spark plug can become fouled. And obviously, you don’t want that to happen. 
  • Low gas mileage: Are you noticing the poor gas mileage for quite a while? It’s time to handle this issue properly. You can get poor or reduced gas mileage for various reasons. Among them, the power valve is one of the important ones. If the value of the power valve is too high, there is a very good chance of getting low gas mileage. So, from now on, keep this fact in mind. Whenever you see reduced gas mileage, inspect the power valve whether it is in good shape or not. 
  • Black smoke from Exhaust: This is the last thing you want to happen. If black smoke gets out from the exhaust of your vehicle, you are in serious trouble. Getting caught by the inspectors is the least of the troubles. Your vehicle can emit black smoke for various reasons. The power valve issue is one of the key reasons. If the value becomes higher than the requirement, black smoke may be emitted from the exhaust. So, don’t forget to check the power valve if black smoke emits from your vehicle. 

How to test the power valve?

The symptoms we have mentioned here, also indicate a blown power valve. So, how will you be able to know the differences? There is only one way to become 100% sure about the power valve condition- testing. Testing is very easy. You are going to need only a vacuum gauge and then you have to follow the steps mentioned below-

Step 1: At first, start the engine of your vehicle. After the start, wait for some time to let the engine reach its normal temperature.

Step 2: It is time to put the idle mixture screws at the right spot.

Step 3: If at this point the engine turns off itself, it means the power valve is in good condition and is operating properly. But if it doesn’t and continues to run, you are in problem. The power valve is not good, blown. And you need to replace the power valve as soon as possible.

Step 4: Now, take the vacuum gauge near the intake manifold’s vacuum port and hook it up. For automatic vehicles, you have to put the vacuum gauge in the drive. And for manual transmission, you have to keep the gauge neutral.

Step 5: When the engine is alive and warm, take the vacuum reading while the engine is in idle.

Step 6: it is time to calculate. You have to divide the reading you got in half. And then, eliminate the decimal point. The reading you get at this point is the correct value of the power valve of your engine. Now you know, how much change you need to implement.

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Power valve vs no power valve

Let’s start with the advantages of the power valve. The main job of a power valve is to control the power that an engine delivers. The power valve also enriches the oil mixture. For doing these things, sometimes the overall HP can be reduced. That is why some people yell about the power valve.

However, the concept of reduced HP is nowadays outdated. We know now how much an emission system-equipped vehicle can even provide. So, for the common users, it is not an issue to be worried about.

Anyway, if you are into racing seriously, you may consider leaving the power valve outside. As you are not a regular user, even the slightest of gains can win you a race. And you definitely want all the odds in your favor in a race, don’t you?

How do I know if I have the wrong power valve?

You know that by comparing the reading you get from a test. Generally, the value of the power valve should be half of the reading of the engine vacuum. For example, if the engine vacuum of your vehicle is 11-12, a 55 (or 5.5”) power valve is the best match for your vehicle. That means any other reading different than the standard indicates a wrong power valve.

What happens if my power valve is too big?

You will see some symptoms if your power valve is too big or the value of the power valve is too high. The symptoms are- low gas mileage, rough idling, spark plug residue, black smoke. If any of these happens, you know the power valve has become too big than the requirement. Or in other words, if your power valve is too big, these incidents will happen!

What happens if my power valve is too small?

The too-small value of a power valve is not a good thing either. If the value of a power valve becomes too low, you will see certain symptoms like too lean air/fuel mixture, backfires while accelerating, and poor acceleration. You have to get rid of these issues as soon as possible as they are in no way beneficial for your vehicle.

When should a power valve open?

If you do have a power valve, most probably it has a number marked on it. This number indicates when the power valve will open. But you have to choose the right power valve for the engine at the same time too. Otherwise, it will not open. The ideal number of the power valve is half the reading of the engine vacuum.

Does power valve affect idle?

No. If you intend to mean whether an “open” power valve affects idle or not, the answer is no. An open power valve does not significantly affect idle. Because the myth about open power valves flooding fuel is not practical. Even though an open power valve may create a slight fuel enrichment at idle, it is nothing serious. And you don’t need to worry about it.

How do you test a power valve?

Testing a power valve is fairly easy. You have to test the power valve to determine whether it is blown or it is the wrong power valve. The testing is necessary because both the wrong power valve and blown one give almost the same symptoms. You can do the testing with only a vacuum gauge. This is available at all the auto parts stores near you.


A power valve may seem insignificant at the first glance. But it is not. It helps you with its various necessary functions. That is why you have to be always careful about the blown or wrong power valves. Because a wrong or blown power valve won’t be able to give you the necessary output.

The power valve is a tiny component of the exhaust system of a vehicle. But this component is very impactful and crucial if you consider its function. A power valve is basically a small piece of metal in your engine which resides in the exhaust port. It controls the size of the exhaust port and the power delivered from the engine in a better way. 

Now you know how important this tiny piece of metal is for the whole vehicle. The power valve will function properly only if it is matched with the engine’s vacuum level.

Watch out for the symptoms, do a test, and change or replace the power valve when necessary. We have tried our best to help you with all the necessary information. If you have any queries, leave them in the comment box!

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