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Engine Backfire & Loss of Power: Everything You Need To Know


We have all heard backfires from cars passing us on the street. In most cases, it is considered noisy and even annoying by many people. Some drivers prefer cars that backfire due to the loud popping noise it makes and the fact that it brings attention to their car.

Backfires often indicate there is something wrong with the ignition system of your car’s engine. Many drivers will notice increased fuel consumption and poor motor performance in these situations.

A reduction in power available to accelerate and maintain speeds is a typical example of cars that are backfiring. There are two different types of what is commonly known as a backfire. A backfire occurs in the exhaust, and there may be flames exiting the tailpipe.

A pop back also referred to as a backfire, is the combustion of gases in the manifold, causing gases to explode through the intake system. We will explore these topics and more in the following narrative.

What is an engine backfire?

Engine backfire is the explosion of gases outside the combustion chamber of one or more of your engine’s cylinders. These gases escape to the exhaust or the intake manifold and combust in the exhaust or the manifold, causing a loud noise and sometimes visible flame exiting the exhaust tailpipe or the intake system.

Why do engines backfire? There are numerous causes for engine backfiring. Whatever the cause, which we will review shortly, unburned fuel-air mixtures are escaping the cylinder where these gases would normally combust.

Instead, combustion takes place in the exhaust manifold, the exhaust pipe, or even the muffler. Unburnt gases can also exit through the valve and ignite in the manifold, causing a loud pop or backfire. Drivers may observe flames exiting the exhaust tailpipe or back through the intake system.

Various components can be damaged, including sensors and air filters, during this process. Newer computer-controlled cars with injection systems tend to backfire less than older models.

What does it mean when a car backfires?

As mentioned earlier, the fuel to air mixture is combusting outside of the engine cylinders, either in the exhaust or the intake system. These are referred to as backfires and pop backs. Drivers encountering backfires should have their ignition systems checked before permanent damage occurs to cylinder heads, intake and exhaust valves, and other components of the intake and exhaust systems.

Backfires can damage valve components causing increased leaks of fuel and air mixtures. The fuel-air mixture combusting outside the cylinder does not contribute to powering the vehicle. Drivers may also notice increased gasoline or diesel consumption and less power available to accelerate the vehicle in these situations.

10 Common Reasons that Cause an Engine to Backfire

Reasons Why Engines Backfire

There are many reasons why engines backfire, which makes this problem difficult to diagnose. Technicians can evaluate check engine light code reports, sensors, catalytic converters, air filters and ensure injectors are clean as well as spark plugs and wires. Checking valve stems and other internal components are more challenging and costly.

#1 Reducing engine speed to fast

Reducing engine speed quickly can cause a rich fuel ratio to exit into the exhaust as the motor adjusts fuel mixtures and timing to the new speed. This mixture can ignite in the exhaust, causing a car backfire and even flame at the exhaust tailpipe.

#2 Rich Air Fuel Mixture (Clogged Engine Air Filter)

Proper combustion calls for the correct fuel to air mixture to meet the demands of the motor. The car’s computer system controls the mixture and relies on several sensors to make sure the correct amount of fuel and air is delivered.

For example, a clogged engine air filter or leaking fuel injectors can cause insufficient air to be delivered, leading to a rich air fuel ratio. Unburnt excess gas exits to the exhaust and ignites, causing backfires. When there is too much gas going into the cylinders, it can lead to engine backfire.

The motor’s power output increases as more gasoline is pumped in so that the pistons are able to push against an even greater force from combustion – but this also means less air gets mixed with your gasoline and diesel mix before ignition takes place. When there is too much fuel and not enough air, the outcome can be disastrous.

#3 Lean Air Fuel Mixture (Clogged Fuel Injectors)

Lean fuel mixtures caused by a failing fuel pump or clogged fuel injectors can cause backfires as well. Lean mixtures combust more slowly, leading to unburned fuel and air, which is also exhausted by the exhaust. When it ignites in the exhaust, a backfire may occur.

When there is too much air, a motor can’t combust efficiently. The internal combustion engine could backfire, and this can be hard on the motor, which makes driving unpleasant for everyone in the vehicle.

The thing about lean mixtures is that they can be tricky to get right. While it’s important to get enough gas and air proportions, the mixture will also depend on engine load- or, more specifically, how many cylinders are firing at a given time.

#4 Really bad engine timing

The engine’s computer system controls the timing of everything, fuel injection, valve opening and closing, and of course, the spark that ignites the mixture in the cylinder.

If the timing is off for some reason, such as sensors not reporting proper information, unburned fuel and air can be exhausted through open valves to either the intake or exhaust manifold. A backfire can be the result when this mixture ignites outside the cylinder.

If you got a delayed timing problem, this means that your motor will start to ignite the gas at the end of the ignition cycle instead of waiting for it to be fully open, which can lead to other problems like power loss, exhaust leak, and increased emissions.

#5 Cracked distributor cap

Distributer caps can become damp, cracked, or malfunction in some manner. The distributor controls the electrical spark delivered to the spark plugs. Either a weak spark or no spark at all can lead to unburned fuel-air mixtures exiting a cylinder and igniting in the exhaust leading to some rather loud backfires.

#6 Problems with the spark plugs

Spark plugs become dirty and corroded as the motor is used. When they are corroded or the gap is set incorrectly, they do not deliver a nice clean, intense spark to ignite the petrol, and the air can jump into the wrong cylinder. As a result, unburnt excess gas and air can be pushed into the exhaust manifold, where it ignites and causes a car backfire.

#7 Carbon tracking on the spark plug wires

Carbon tracking essentially causes short circuits between the spark plug wires or to metal parts of the motor. When this occurs, a weak or no electrical signal gets to the plug, and the fuel-air mixture does not ignite in the cylinder or only partially burns the gas.

When the exhaust valves open, this unspent fuel is pushed into the exhaust manifold, where it ignites and causes a backfire. It’s crucial for a car to have a motor that is well-tuned. When the spark fires in the wrong cylinder and at the wrong time, this sure leads to backfires and other problems!

#8 Bent Or Damaged Intake Valve

Intake valves can become damaged due to high engine temperatures or corroded with carbon deposits. The result is a poor seal when the valve closes, allowing fuel and air to exit into the intake manifold where it combines with more combustible and air exploding, causing a pop back or backfire.

#9 Gasoline contains high blend levels

Every motor is optimally designed to utilize a particular blend of gasoline. Using a high octane blend in a car engine designed to work with low octane can cause improper amounts of petrol and air mixtures to be sent to the combustion cylinders, leading to unburnt gas exiting the exhaust cylinder to later explode in a backfire.

#10 Bad adjustment of the carburetor

Older car engines and non-computer-controlled engines use a carburetor to control the fuel to air mixtures. The carburetor needed adjustments from time to time to reflect the engine condition. Any changes or maintenance such as adding new plugs, air filters, or fuel pumps required the carburetor to be adjusted. A badly adjusted carburetor could cause a too lean or too rich mixture, leading to backfires.

Can a backfire damage an engine?

A single backfire should not cause any damage. However, an engine that is often backfiring may damage the exhaust, the intake system, and even damage the valves which control the entry and exit of gases.

While exhaust systems can be expensive to repair, valves bent due to excessive backfires are much more expensive to repair. In addition, your gasoline consumption also increases. If the dashboard warning light illuminates and the engine is backfiring, have the engine repaired immediately.

What causes an engine to backfire through the intake?

Bad ignition timing can cause an engine to backfire through the manifold system. The spark plugs are timed to deliver a spark at exactly the right moment when the piston is in the correct position within the cylinder. Both the exhaust and the intake valves are closed at the moment, causing the full force of the combustion to push the piston and turn the engine crank.

If the plug delivers a spark early before the intake valve is fully closed, unburnt gas and air are exhausted through the intake valve into the manifold, where it can combust and cause a pop back or backfire since many consumers do not distinguish between the two.

Damage to the intake sensors, the oxygen sensors, and even the air filter can occur in these situations, leading to further potential issues with timing, gasoline consumption, and loss of power from the motor to the transmission.

Can bad gas cause backfire?

The term bad gas can mean a lot of things. For example, the gas may contain water, impurities from the gas tanks, such as dirt and rust. If the gas has been sitting for some time, exposed to oxygen, the gasoline will slowly degrade with varnishes and gums forming in the liquid. Any of these can lead to backfires.

The gums, dirt, and varnishes may clog the fuel filter, causing the fuel pump to work harder to deliver gasoline to the motor. Gums can also cause the build-up of carbon deposits on various components. These factors can lead to lean fuel to air mixtures which we previously discussed can cause backfires.

In addition, the gasoline may not completely burn during the combustion process. Unburnt petrol and air exit through the valve into the exhaust manifold where it may ignite and cause a backfire sound to emanate from the tailpipe.

What causes backfire through the exhaust system at idle?

Whenever fuel and air escape from the cylinder to the intake or the exhaust manifold, backfires can occur. Several causes include the following:

  • Clogged or bad fuel pump
  • Failing fuel pump
  • Inaccurate timing
  • Exhaust valve not sealing properly

Any of these issues can lead to a lean or rich fuel mixture. In both cases, not all of the gas burns completely when it ignites inside the cylinder. The exhaust valve opens and allows the unburnt gasoline to exit into the exhaust manifold where it can ignite, causing an explosion inside the exhaust system and creating what we call a backfire. Occasionally flame will exit the tailpipe as well.

What causes an engine to backfire through the exhaust system on a startup?

Every time a car is started, a rich fuel to air mixture is ignited inside the cylinders that cause the engine crank to rotate. Engine timing systems, fuel to air mixtures must be correct, and valve systems must operate on cue.

If a spark plug fires too late, if the fuel to air mixture does not combust fully if air mass sensors do not do their job perfectly, unburnt gas to air mixtures pass from the combustion cylinder into the exhaust manifold. These gases may ignite spontaneously inside the exhaust system, causing a backfire out the tailpipe.

Once the car has started, the motor may normalize or continue to backfire. In either case, it is recommended to have your vehicle checked by a mechanic. The mechanic can check for trouble codes that illuminate the warning light, check the timing, the ignition system, and that all other sensors are operating properly.

Can a bad distributor cause a backfire on engines?

The distributor in your car’s engine is responsible for distributing high voltage current to each spark plug. The timing must be perfect. Each spark plug provides a spark when the piston is in the correct position inside the cylinder, and both the intake and exhaust valves are closed.

Distributors deteriorate over time due to wear and tear. Arcing between electrodes may occur, affecting the time of the spark on several spark plugs. A cracked distributor cap also disrupts the distribution of the high voltage current.

The gas in the cylinder may partially combust or not combust at all. Once the exhaust valve opens, all of the mixtures exit into the exhaust manifold, where it can spontaneously combust, causing a backfire.

Unburnt fuel can also exit through the intake valve leading to pop backs or backfires within the manifold. Your engine will also lose power, and gasoline consumption will increase as well.

How do you fix an engine backfire?

Since backfires are caused by unburnt fuel combusting outside the combustion cylinder, there are several areas to check when you are attempting to fix most engines backfire issues. Backfires can cause damage to your motor, so it is important to take action immediately. These steps check all of the common causes and include:

  • Check the trouble codes
  • Revise the fuel pressure and the fuel system
  • Ensure the air intake boot is not torn or ripped
  • Check for a vacuum leak in the air intake system

The above checks can be simple, straightforward solutions that are easy to repair and inexpensive. More serious concerns involve the following checks.

  • Check the camshaft for worn exhaust valve lobes
  • Check for worn valves or bent valve stems


The air/combustible mixture must meet design specifications at the time the spark plugs initiate combustion, and the timing must be perfect. In modern cars, the car’s computer controls the timing and the air-fuel mixture, relying on numerous sensors to report current conditions and motor requirements.

Both lean and rich fuel mixtures can cause engine backfires. Engine timing that is off can also cause backfires. The causes of these problems can be due to failing components, bad gas, and poor maintenance. Gas in the exhaust system ignites and produces a loud bang, commonly referred to as a backfire.

Engines that backfire can also cause additional damage to intake and exhaust system components and sensors. Severe backfires can damage valve seats, valve rods and become quite expensive to repair. Have your vehicle serviced immediately if you experience backfires or pop backs to avoid significant permanent damage to your motor.

Last Updated on: November 17, 2022

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