What Causes Gas To Come Out Of Exhaust? Reasons & Solutions

If you see gas emerging from your exhaust pipe, then it’s a serious problem. Since it’s not normal, this may indicate damage to your vehicle. 

Don’t worry though. There are solutions to this matter. Before fixing the issues, you need to be aware of the reasons. 

So, what causes gas to come out of exhaust

There can be several reasons behind gas coming out of the exhaust. First, check the air filter. A dirty air filter can cause the gas to come out. It might have an incorrect amount of air or fuel. Then, check the air-fuel ratio inside the combustion chamber. Finally, check the fuel injector for damage.

This was just a short summary of the things we will discuss. Join us in the adventure of fixing these smoke issues in detail!

Let’s get right into it!

Things You Should Know Before Fixing the Issue

I know you may be tempted to fix the exhaust problem. Still, you need to know the things I have mentioned below. 

Knowing these things will help you a lot along the way.

  • If you see white gas coming out of exhaust, it must be water vapor. The issues regarding water vapor are far less serious than the fuel ones. 
  • When you see any kind of liquid coming out of exhaust, observe it. You can find this out by looking for the color of the smoke. It could be water or fuel coming out of exhaust. 

Here’s a table to give you a clear view on that issue.

Smoke ColorKind of Liquid

Source: Cartreatements.com

3 Possible Reasons Why Gas is Coming out of Your Exhaust

A lot of reasons can be affiliated with the exerting gas from the exhaust. It can be easy or complex. Still, if you can pinpoint the problems, you can fix them efficiently.

Below, I’ve mentioned the most common causes behind gas coming out of the exhaust. On top of that, the solutions for them are also included.

So let’s not waste any more time and take a look at them.

Reason 1: The Air Filter is Defective

When the air filter is defective, the engine and combustion chamber don’t receive sufficient air. This is one of the most common reasons for gas coming out of the exhaust. 

Let’s walk you through the solution for this issue.


The dirt and gunk buildup inside the filter can block the airflow. No airflow makes the air filter useless. For the solution, you have to change the air filter. Although it is possible for you to clean the air filter, it’s not recommended.  

The air filters are cheap and easy to replace. On top of that, you can get air filters in any automotive store or online. 

These are some of my recommended air filters for your convenience:

Spearhead Max Thrust Performance Engine Air FilterFor All Mileage CarsGet it Now
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By using these air filters, you can be tension-free about the airflow happening inside the engine.

Additionally, the air filter might be clean but it can be misplaced. A misplaced air filter won’t function properly. 

To correctly place the air filter, follow the manual of your machine. Or you can check this video for better understanding-

You can also take help from a technician if it seems too complex.

Try running the engine. Do a test drive. See if the issues of the exhaust are solved or not. Try not to mix up the gas with the exhaust fan smoke. There should be some amount of smoke.

Reason 2: Combustion Chamber Ratio Error

If you’ve followed the first solution, the shortage of airflow issue is handled. However, that might not be the case with the amount of fuel situation. 

Poor air coverage inside the engine causes some issues; specifically in the combustion chamber. Less air in the combustion chamber messes up the fuel/air ratio of an engine. 

If you overfill the fuel tank, the ratio will be improper. That can also be another reason.  


If the ratio is messed up, burning the excess fuel can come in handy. If you see gas coming out of exhaust of lawnmower, this solution will help too. 

Follow the instructions to successfully restore the ratio.

A perfect ratio of air and fuel is needed inside the combustion engine. If the engine has too much fuel and less air, it’s called running lean. 

On the other hand, the engine can have too much air and less fuel. In that case, it’s referred to as running rich.

Now, onto the real solution-

  • First, turn on the engine, whether it’s your car or a lawnmower. 
  • Then, let the engine run in neutral. Letting it run will burn the excess fuel and bring the ratio back to normal. Because the engine was running rich.
  • You can try accelerating a bit in the middle to increase efficiency. Don’t panic if you see the breakout of smoke from exhaust when accelerating.
  • Finally, turn the engine off when you’re done. 

Since there is extra fuel, you might see the extra fuel coming out of exhaust manifold. That is obvious too, so don’t worry. Don’t burn too much fuel, or the engine will run lean.

Be careful not to overheat the engine. That can cause new problems for your vehicle or machine.

Reason 3: The Fuel Injector is Damaged

If the solutions stated above don’t work, the issue might be with the fuel injector. When a fuel injector is damaged, it resists the fuel lines which increases fuel consumption. 

The engine also operates roughly. It makes harsh noises when running on fuel. The honda accord startup grinding noises can be an example of a damaged fuel injector.

Source: Dieselogic

Eventually, it causes the engine to let out gas through the exhaust. That’s the reason you might see black or white smoke out of exhaust on startup. You’ll have to fix the fuel injector in this case.


Unfortunately, the only solution for this is to replace the fuel injector. A fuel injector cannot be repaired. 

It has to be replaced with a new and exact same unit. The cost of replacing the fuel injector is around $100-$150.

You can try to replace it totally all by yourself. Here’s a step-by-step guide that you can follow-

  • Firstly, you need to remove the connector.
  • Now remove the fuel rail and lift up on the rail.
  • Next, remove the existing fuel injector and the O Ring seal.
  • The next step is to install the new fuel injector and push it down.
  • Finally, reinstall the bolts and reconnect the electrical wirings.

And that’ll be all needed to replace the fuel injector.

But no worries! You can always take your car to a workshop if you think all these are a big hassle.

You might also have to buy a new gas tank along with it. It costs from $300 to $450. If you buy a gas tank, take good care of it. Clean it well before using it. You should avoid a rusty gas tank afterward.

Although these expensive fixes will make your engine feel brand new. Also, normal exhaust smoke will come from the exhaust instead of gas.

These are some common reasons and solutions when you see gas coming out of exhaust!


How do you know if you have an exhaust leak?

There can be many reasons behind an exhaust leak. Accordingly, there are signs for each one. If you’re losing speed and notice inefficient acceleration, your exhaust might leak. This also increases fuel consumption. Also, the engine makes loud noises when the exhaust is leaking. 

How much do exhaust leaks cost to fix?

It can cost up to 400 dollars to fix an exhaust leak. It can range from 100 to 400 dollars. However, you need to count additional fees to fix your leaking exhaust. The parts and the labor cost have to be paid for. Labor costs can average around 100 dollars per hour. The prices of the parts vary. 

Why is my car so loud when I press the gas?

It can be an exhaust/vacuum leak if it makes loud noises when accelerating. Vacuum leaks usually occur because of damaged, disconnected, or broken vacuum lines. If the car has symptoms regarding acceleration and speed, it should be an exhaust leak. Fixing an exhaust leak can be tricky.

Final Words

We’ve reached the end of this article. By now, it should be clear what causes gas to come out of exhaust.

You might find symptoms or reasons which are not mentioned in the article. In that case,  consider consulting an experienced car mechanic!

Good luck fixing the exhaust issue!

Robert Lozano

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