Why Car Backfires?


A car backfire is a loud, sharp noise made by the exhaust system of an internal combustion engine. A car’s exhaust system has many features that help prevent backfire. However, they sometimes fail, causing you to hear a pop, bang, or roar coming from the back.

A car backfires when the fuel/air mixture in the combustion chamber is at a lower than normal ratio. This causes the pistons to fire at a higher ratio but without enough oxygen in the chamber. As the unburned fuel combusts outside the car’s pistons, it causes a sharp, loud noise. 

Read on to find out how backfires can cause other problems for your car and ways to prevent them.

What Causes a Car To Backfire?

A backfire is often a tell-tale sign that something is wrong with your car. Therefore, it’s essential to know the possible causes of a car’s backfire. This will help address the problem before it worsens.

Here are some of the most common causes of a car backfiring:

  1. Faulty spark plugs or ignition wires
  2. Dirty air filter
  3. Clogged fuel injector
  4. Malfunctioned fuel pump
  5. Incorrect timing
  6. Loose or misaligned valves

Here are more details on the mentioned causes of car backfire:

1. Faulty Spark Plugs or Ignition Wires

Spark plugs and ignition wires are essential for providing the car with a robust and steady spark that ignites the fuel-air mixture in the chamber. If either of these components is worn or faulty, your car may backfire when you try to start it up.

Suppose your car’s spark plugs are defective. In that case, the car won’t produce a spark needed to ignite the fuel-air mixture. As a result, your car’s engine won’t start. 

Consequently, when the pistons begin their compression stroke by pushing into an empty chamber, they create a loud noise that sounds like a backfire.

Read: Why Is There Oil On My Spark Plug Threads?

2. Dirty Air Filter

Your car’s air filter is essential to keep dust, debris, and other impurities from interrupting the airflow into your car’s engine. If your air filter is clogged with dirt or any other particles, it won’t be able to supply a steady supply of clean air to your car’s engine.

Because of that, the amount of air in the fuel-air mixture will be lower than expected. As a result, your car’s pistons may not produce sufficient power to start the engine, causing a backfire as it revs up.

Read: When Should You Replace The Engine Air Filter?

3. Clogged Fuel Injector

The fuel injector provides the fuel to your car’s engine. If it’s clogged with dirt or other particles, there won’t be enough fuel that reaches the piston chambers for ignition. This may cause a backfire when you start your car.

Therefore, it’s essential to regularly inspect the fuel injector for clogs to keep it clean. Also, if you suspect anything is blocking your car’s fuel intake, turn off the engine immediately and contact a mechanic.

Read: Can You Drive a Car With a Bad Fuel Injector?

4. Malfunctioned Fuel Pump

A malfunctioning fuel pump is another reason why your car may backfire when you start it up. If the fuel pump malfunctions or ceases to work, your car won’t be able to supply enough fuel for its engine.

As a result, the amount of gas in the combustion chamber will be lower than expected, resulting in a backfire.

5. Incorrect Timing

Your car’s timing refers to when the spark plug fires relative to the piston position in your engine. If your car’s mechanical or electronic timing is off, it can cause the misfiring of one or more cylinders. This, too, will result in a loud noise.

Here’s a YouTube video that explains how to tell if your engine timing is off:

6. Loose or Misaligned Valves

Valves are components that open and close on each engine stroke to provide airflow into the piston chamber. Therefore, you should always tighten your valves securely to prevent them from becoming loose.

Loose valves may open at the wrong time and allow air into one cylinder but not the others. This will cause irregular combustion in the pistons, which causes them to make a loud popping noise when they fire up.

This YouTube video by Engineering Explained describes why cars backfire in detail:

Read: Bad PCV Valve Symptoms and Fixes

Can a Backfire Damage My Engine?

Now that you know what car backfire is and some of the possible causes, does it hurt the engine?

A backfire can damage your engine. Notably, this phenomenon requires extra work from your engine compared to normal operating conditions. For example, your engine has to produce more power than usual to compensate for the lower effectiveness of the combustion process.

In addition, a backfire can damage the fuel injectors, pistons, and other components in your engine due to irregular combustion, causing a decline in performance.

How Do You Stop a Car From Backfiring?

If your car is backfiring, you need to curb the problem before it gets out of hand. This will prevent your engine from damage caused by irregularities in the combustion process.

Here are a few ways to stop a car from backfiring:

  1. Check the air filter.
  2. Check the spark plugs.
  3. Check the fuel injectors.
  4. Clean the throttle body.
  5. Replace the oxygen sensor.
  6. Have a mechanic check for any other problems.

Here’s a rundown of how to go about each method:

1. Check the Air Filter

This is one of the easiest ways to stop a car from backfiring. Simply replace your air filter if it’s become too dirty or clogged to allow the engine’s cylinders to get enough air for them to fire properly.

To do this, follow these steps:

  1. Disconnect your battery.
  2. Remove the air intake hose.
  3. Remove your car’s engine cover.
  4. Locate the air filter casing.
  5. Remove the air filter from the casing.
  6. Inspect the filter for any dirt or debris.
  7. Clean it with a brush or compressed air.
  8. Replace it and reconnect your battery.

2. Check the Spark Plugs

You can inspect them by removing your car’s engine cover and inspecting each cylinder one by one. 

If you notice a dark brown or black color on the tip of a spark plug, it indicates that it might be firing improperly due to an obstruction. You’ll need to remove each spark plug to clean them. Replace your spark plugs if necessary to ensure your engine works correctly.

Read: Car Diagnosis Cost

3. Check the Fuel Injectors

Since the fuel injector requires more force to dissipate an obstruction, you should clean or replace it if it’s not functioning correctly. To do this, follow these steps:

  1. Disconnect your car’s battery.
  2. Locate the fuel injector in your engine compartment.
  3. Inspect it for any dirt or debris.
  4. Clean it with a brush or compressed air.
  5. Replace it and reconnect your battery.

Tip: For the best results, I recommend cleaning your fuel injectors using the AUTOOL Fuel Injector Cleaner and Tester (available on Amazon.com). It comes with a microcomputer that automates cleaning and tests your injector to ensure you have removed all dirt and debris, making it a convenient tool.

4. Clean the Throttle Body

You can do this by removing the air intake hose and cleaning out any dirt or debris that might be present in your throttle body’s air intake system. Here’s how:

  1. Remove the air intake hose.
  2. Dump any loose dirt out of the throttle body.
  3. Clean it with a brush or compressed air.
  4. Replace the intake hose and reconnect your battery.

5. Replace the Oxygen Sensor

A faulty oxygen sensor may be reading incorrect amounts of gas entering your cylinders. This, too, will cause a rough idle or backfire to occur.

Replacing or cleaning your oxygen sensor will prevent this problem from occurring again. So, keep in mind that your car’s oxygen sensor needs to be replaced after 100,000 miles (160,934 kilometers).

6. Have a Mechanic Check for Any Other Problems

If you have tried all these steps, but your car is still backfiring, it’s time to bring it to a professional.

The mechanic can inspect your car to find out if any other problems are present. They’ll also determine the best course of action to prevent your car from backfiring again.

Read: Car Full Service Cost // Whats included?

Key Takeaways

A car’s backfire is caused by issues in either the fuel or oxygen supply to your engine. This forces the engine to work harder than usual, leading to cylinder misfiring due to irregular combustion.

The most common causes of car backfires include:

  • Dirty air filter
  • Clogged fuel injector
  • Faulty oxygen sensor
  • Dirty or obstructed throttle body.
  • Faulty spark plugs
  • Malfunctioned fuel pump
  • Incorrect timing
  • Loose or misaligned valves

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