Car Engine Backfire: 3 Causes and How to Fix

What causes engine backfire

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The loud sound, flames coming out of the exhaust… An engine backfire is a real treat for our senses for sure, but is it actually good for the car? What causes it?

A lot of questions come to our mind when we see an engine backfire. There was a time when I wished if I could do the same, loud sound and flames, but only till I found out that it’s not good for the car, and might be due to engine damage as well.

This article will answer all of your questions regarding engine backfires, like the possible causes, solutions, what happens if you don’t fix it, etc.

What is Engine Backfire?

The combustion of the air-fuel mixture, which ultimately causes the vehicle to move, is supposed to happen at the combustion chamber only. An engine backfire happens when the combustion takes place outside of the combustion chamber. It makes a loud sound, and we can see flames coming out of the exhaust.

What causes it?

Engine backfires can happen due to multiple causes, varying from an unbalanced fuel-air mixture to engine problems.

Bad engine timing

Inside each of your engine’s cylinders, you’ll see at least two valves, one for the intake of the air-fuel mixture and the other to let the fumes out to the exhaust. The intake valve will shut when the air-fuel mixture gets inside the combustion chamber. The sparks(from spark plug) will initiate the combustion. Once the combustion is done, exhaust valves will open, let the fumes out, and close.

If the timing of the spark is a little late, the air-fuel mixture will not combust on time and the exhaust valve will open. If the combustion takes place while the exhaust valve is open, the engine backfires.

The combustion chamber will be ultra hot from the previous combustions, and even if the air-fuel mixture gets to the exhaust without burning, any tiny spark or even the heat itself can make the mixture burn, and the engine backfires.

Imbalance in the air-fuel mixture

If you have been experiencing low mileage, that is probably due to the imbalance in the air-fuel mixture. Each drop of fuel needs a specific amount of air to burn it. When there is not enough air to burn the fuel completely, you’ll see flames coming out of your exhaust.

This can be due to two reasons: either more fuel is reaching the combustion chamber or less air is there to burn the fuel. You should get your vehicle inspected by a mechanic to know the exact cause, but we will give you a rough idea of the possible reasons.

If your vehicle has a fuel-injection system, there might be a leakage causing more fuel to flow into the chamber. Or, your air filter could be clogged, causing your vehicle to choke. In both cases, the unburnt fuel could reach the exhaust and you have an engine backfire.

Oh, and if you are getting a low mileage even without engine backfire this is where you have to look at first. The air-fuel mixture has to do 90% of the job when it comes to mileage.

If there’s white smoke coming out of your exhaust, it might be pointing to a bigger problem and you should fix it immediately.

Older Engines

If you are using an old car, there could be a lot of issues causing the engine to backfire.

Most of the older cars come with a carburetor, which mixes the fuel with air. Modern cars are using computer-controlled systems for this, and so the probability of imbalance in the air-fuel mixture is narrow.

But for cars with a carburetor, it needs periodic cleanings to work smoothly. As time passes, the carburetor will get clogged from the dust and dirt from air and fuel, and it will cause a bad air-fuel ratio.

Of course, it will be associated with low mileage. Take your vehicle to a good mechanic and he will clean it for you in less than an hour.

How to fix?

Well, the best thing to do is to take your car to a mechanic. But if you know a thing or two about cars, you can fix it easily.

The first thing to do is to find what exactly causes the problem. Start with the spark plug. If it is black in color due to carbon deposits, try cleaning it, and if it is too clogged or old, consider replacing it.

The spark plug gap also plays a role in the engine backfire, so check if the gap is the same as recommended by the manufacturer. It will be around 0.025” in most cases and should not exceed 0.055” unless mentioned by the manufacturer.

The second thing to check is the air filter. Carefully remove the air-filter and try cleaning it. It is always better to replace the air filter once in a while, especially when it gets clogged. You will see a significant improvement in the initial pick up.

Cleaning the air filter and spark plug every 10,000 miles is a good practice. It will keep your engine smooth and mileage sharp.

If the problem still persists, you should take your vehicle to the mechanic to check the fuel injection system.

What about high-performance sports cars?

You might have seen Lambos and Ferraris spitting flames out of their exhausts. It’s thrilling, right? Most of the sportscars backfire and let’s see what causes it.

Sports cars, unlike normal cars, are manufactured for high performance which takes a lot of fuel in. The average mileage of a Lamborghini Aventador is 11 miles per gallon, which literally means that a lot of fuel is there at the combustion chamber every second.

When the sportscar brakes from a high speed, the ECM takes some milliseconds to correct the mixture ratio, the large volume of fuel which would have burnt if the car didn’t brake, goes into the exhaust unburnt, and causes backfire.

The reason why it does not happen with normal cars is that the volume of fuel at the combustion chamber will be significantly less than a sports car.

Summary

The most common cause of engine backfire is the imbalance in the air-fuel ratio, and it can be fixed easily by a mechanic. It might also be due to a damaged or clogged spark plug, and it can be fixed in minutes by replacing the spark plug.

In older engines, the carburetor needs to be cleaned periodically, and if not, it can also cause the same problem.

Got any questions? Let us know in the comments.