Why does my car backfire when I shift?

Imagine this, you are driving down the road and you a car is shifting through the gears. After a gear change, you hear a popping sound. It might sound like you ran over something or it might sound like something broke. Although, this is typically called a backfire.

Why does my car backfire when I shift? This is because there is unburnt fuel in the exhaust. When the fuel leaves the engine the heat from the exhaust ignites it. This creates an explosion which is the backfire you hear. Normally your RPM drops during a shift. If there is unburned fuel by the time the engine slows down your car can backfire.

Backfire or Afterfire?

Back in the day a backfire used to refer to an explosion near the intake of the engine. In some scenarios the fuel would ignite before the cylinder which could cause an explosion out the front of your intake. Unlike and afterfire you’d hear the explosion under your hood.

Afterfire is the name of the explosion that happens after the cylinders. This is where the unburnt fuel travels out of the exhaust. In the right conditions, It can create a popping noise. If your engine is running rich chances are you might have some afterfires.

In modern times people typically call “afterfires” “backfires.” So when someone says that a car backfired they usually mean that there was in pop inside or at the end of the exhaust. In the rest of the article, we will continue to use the term “backfire” for an “afterfire”

What is a Backfire?

A car backfire is when your engine has unburnt fuel that makes its way to the exhaust. When the exhaust is hot enough it ignites the fuel causing a small explosion. This typically happens when your engine is running rich.

What is Running Rich?

Running rich refers to your engine having excess fuel that isn’t burned up during the combustion process. Engines have an air/fuel ratio. This means that there are so many parts fuel to air. With the correct ratio, your engine will run the best.

But if you have more fuel in your ratio there won’t be enough air to completely burn it up. The leftover gas is what exits your engine. When you are running rich you have the highest chance of backfiring. While this won’t necessarily hurt the engine it can cause your gas mileage to go down and other components can be affected.

Your engine’s computer determines how much fuel to add to keep the engine running. If there is a bad or dirty sensor the computer might not be able to get the correct data. In turn, it will provide more fuel than is needed.

What is Running Lean?

Running lean is the opposite of running rich. This means that there is not enough fuel for the amount of air. This is more dangerous for your engine. If you don’t have enough fuel the engine won’t run correctly. In some more extreme cases, you can even blow up your engine.

If you are having an issue where your engine is running lean then you may have a fuel delivery issue. That or you may have a bad sensor.

Is a backfire dangerous?

Any explosion can be dangerous. If you stand too close to the exhaust when it’s backfiring you could get burned. Not only that but some backfires are so loud that they can cause ear damage. Although, if you know anything about racing, especially top fuel dragsters, cars can get pretty loud.

Backfires can also hurt parts of your vehicle. Depending on where the explosion occurs it could damage parts like your oxygen sensor, muffler, and exhaust altogether. Backfires cause excessive heat which can cause some excessive wear on parts.

How to stop backfires.

If your car is having an issue with backfiring there are a few things you can do. The first is to make sure that certain components are clean. You can start by checking your air filter. Your air filter is the first place where air enters your engine. If your filter is clean your engine won’t be getting adequate airflow.

The next part is your mass airflow sensor. This sensor, which is normally by the air filter box, reads how much air enters the engine. If the is dirty then it may read and relay the information incorrectly. Something as simple as cleaning off the sensor which a dedicated Mass Airflow Sensor cleaner may solve your problem.

The next option is to have a mechanic take a look at your car. They will be able to pull up diagnostics to see if there are any bad sensors. A mechanic should be able to locate the source of the issue and repair it for you.

How to cause backfires

Now if you’re a car guy or just want your car to backfire there are a few options you have. Bear in mind that there are different laws in your area so make sure you are sticking to what’s in your local code.

Getting your car to run a little rich is a good way to get some backfires. Normally you can hire a tuner and they can change the settings on your car’s computer. The data will be adjusted so that it applies more fuel than is necessary. This extra unburnt fuel will cause your car to backfire.

Another choice is to buy a backfire kit. These kits add fuel directly into your exhaust to cause backfires. Again this isn’t good for the life of your exhaust. But if you want your car to back no matter the cost then investing in a backfire kit may be the way for you.

To sum up

Why does my car backfire when I shift? This is because there is unburned fuel in your exhaust system. This in combination with the heat causes the fuel to ignite causing a backfire.

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