5 Reasons Why Your Car Backfires. Number 5 Will Get You Worried

What causes a car to backfire? In a nutshell, your car backfires when its internal combustion engine experiences an instant of external combustion. External combustion is when combustion happens anywhere else but the combustion chamber.


All the same, some cars backfire by design. In modern cars, for example, the manufacturer may design it to have some backfiring upon deceleration to add to the sporting sound. I know now you have the mental picture of a race car with the crazy rumbling sound at times flames spilling out of the exhaust.

Backfiring is all good as long as it is moderate and doesn’t affect the performance of the vehicle, but when it gets inordinately excessive, it is time to get to the root cause of the backfire – you might have a problem.

5 Causes of Backfires in Car

The proportion of air-fuel is defined as the mass of air to that of gasoline that is mixed in carburettor for the purpose of combustion.

This proportion is very significant since we have limits on the amount of fuel needed to support full combustion and efficient firing. When the fuel is too much, we have a rich air-fuel ratio and when the fuel is too little we have a lean air-fuel ratio.

The extent of richness or leanness determines the amount of backfires and misfires or lack of it all together.

Engine operation can happen with the range of 8kg of air to 1kg of fuel to 18.5kg of air to 1kg of fuel (8:1 to 18.5:1 respectively.)

1. Running Rich

When your engine receives excess fuel than it can effectively burn, it is said to be running rich i.e. a high fuel to air ratio. When your engine runs rich, you have inadequate air to produce an explosive, and fast combusting flame.

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This results in the fuel burning slower meaning that it will be partially burnt before completing the exhaust bit of the engine.

Now when the exhaust valves open to let out exhaust gasses, the extra air in the muffler allows the unburnt fuel to burn explosively resulting in the popping sound, and sometimes flames, spitting out of the exhaust. Running rich is caused by different issues (some as simple as a dirty air filter).

2. Incorrect Engine Timing

Engine timing allows the engine running cycle (fuel in – compression – ignition – exhaust) in the cylinder head isn’t synchronized with the cylinder block.

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The major engine timing issue that may cause your car to backfire is retard timing or delayed timing. What this means is that the ignition cycle in your combustion chamber starts late and ignition may happen as the exhaust valve opens.

This cause the unburnt fuel to burn explosively resulting in the popping sound, and sometimes flames, spitting out of the exhaust. Engine timing can be corrected easily by your mechanic.

All the same, you will want to be on the lookout for other causes of the backfire since some are pretty straightforward as you are about to find out…

3. A Cracked Distributor Cap

Some vehicles don’t have ignition coils on the spark plugs by design. If your car is like one of these, it uses a distributor cap and a set of wires to distribute electrical pulse throughout the spark plugs.

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Some vehicles don’t have ignition coils on the spark plugs by design. If your car is like one of these, it uses a distributor cap and a set of wires to distribute electrical pulse throughout the spark plugs.

These electrical pulses are very important because they make the spark plug to produce the spark that ignites the fuel.

Assuming that you have a cracked distributor cap, moisture can leak in through the cap causing a spark from one cylinder to track another spark from a different, incorrect cylinder.

  • The incorrect cylinder will most likely fire out of sync (when the exhaust valve is open) and Boom! You will get a backfire.

I had this problem on my Car. I solved the problem by buying a genuine distributor cap assembly from Amazon. I made it a habit to check the cap every time I went for service as part of my preventative maintenance.

4. Carbon on Spark Plug Wires

As the car ages, environmental factors may cause sparks to transverse from one wire to another one if they are close to each other. When this happens regularly, a carbon track that acts as a shortcut to the spark will cause a misfire that resembles the one in a cracked distributor cap I mentioned above.

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In other cars that don’t have a distributor cap, the scenario is almost the same. Since such cars have ignition coils bestrode directly onto the spark plug, the sparks may disperse and take a shorter, but incorrect path.

After the dispersion, the residue spark plug isn’t adequate to ignite the fuel, resulting in residue fuel in the cylinder. Despite the next ignition being sufficient to fire the plug, the process will happen, albeit with rich fuel and again, the fuel will not burn completely by the time the exhaust valve opens.

  • This extra air that is present when the valve opens causes a backfire.

5. Damaged or Malfunctioning Air Gulp Valve

If your car was made in the early 2000’s or earlier, chances are that it comes with an air injection unit that feeds into your exhaust system when the engine is under load. This is necessary in order to burn excess fuel, resulting in a better emission system. The air injection system has an air gulp valve.

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This is a one way valve that allows air into the system in instances when the engine is on load. When the gulp valve is malfunctioning, air is released into the combustion system even during de-acceleration resulting into a backfire due to the ignition of unspent fuel.

PS: if your car has one manifold you will have one air gulp valve. If it has two manifolds, you will have two air gulp valves.

Diagnostic and Troubleshooting

When your car suddenly develops backfires, you should perform the following troubleshooting checks with 5 steps here:

  • Step 1
  • Step 2
  • step 3
  • step 4
  • step 5

Check the Engine Warning Light

When your engine starts backfiring, the first thing you should do is check the engine warning light. Almost all cases of backfire will cause the engine warning light to turn on.

A backfire is a sign that your car engine is not running optimally and it needs to be checked. If your engine warning light is still not on, continue down this guide.


A backfire from your exhaust pipe will not hurt your car, but it can be an indicator of an impending problem or a precursor to a more serious problem.

You should always ensure that your car is operating optimally by doing regular servicing and preventative maintenance. I tried to keep this guide as simple as possible to help you understand your car better.

Feel free to share this guide with your friends and in case you have any question, leave it in the comment section. Let us keep the conversation going on.

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