Why Do Cars Backfire?
A car backfire is usually due to engine failure, a dirty air filter or fuel filter, leaky exhausts, or bad engine timing.
Written by Christelle Agustin
Reviewed by Melanie Reiff
Cars backfiring is a sign of a leaky exhaust, a dirty air filter, or bad engine timing—all of which need to be replaced or diagnosed by an experienced mechanic.
The sound of a car backfiring can come in the intense form of a gunshot pop or a subtle gurgle. While newer computer-controlled engines have gotten better at preventing engine backfires, other factors can contribute to the problem.
If you want to prevent backfiring, the most important thing is to keep your vehicle up-to-date with regular repairs and maintenance.
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What causes a car to backfire?
Explosions are a normal part of the process that allows cars to move from point A to point B. The mix of fuel, air, and the car’s cylinder—the part of the engine where fuel is turned into horsepower—come together to fire up your engine and get your wheels moving.
The problem arises when the supposed-to-be-controlled explosions travel outside of their designated valves and containers. This is when a backfire will occur as a deafening pop or a burst of fire through the muffler.
It’s usually unexpected and startles you, but backfiring can warn you of some issues that should be addressed. Here are a few reasons why your car may have backfired.
Dirty air filter
A clean
air filter
is vital for your engine to function properly. Engines require a good balance of air and fuel mixture. If dirty air flows into your engine, it contaminates the air-to-fuel ratio and results in a backfire.Leaky exhaust
A leak in the exhaust system opens your engine up to an extra flow of air—which isn’t good. Since your car must maintain the right ratio of air and fuel, an excess of air or fuel throws the balance off and can cause gas to ignite and backfire.
It is important to fix the leak as soon as possible since exhaust fumes pose health risks to you and your passengers.
Dirty fuel filter
A
fuel filter
keeps dirt, debris, and other contaminants from entering the engine. A clogged or dirty fuel filter can lead to insufficient levels of fuel flowing through the engine, affecting the fuel-to-air ratio.Bad engine timing
After putting your key into the ignition, an entire system of valves times the compression and combustion of fuel and air to kick your car into gear. If the timing of even one part of the combustion system is off, the fuel-air mixture escapes and results in a backfire.
Older car engine
Older engines are more prone to backfiring due to longer
spark plug
wires and wires simply not being installed properly. What’s more, the tendency for wires to bend and touch other wires can cause a short circuit or a badly-timed spark to go off.You can rest easy if you have a new car. Nowadays, vehicles come with computer-controlled engines, which means significantly fewer wire complications and a rare occurrence of backfires.
Under-the-hood issues
Cars are complex, and it can be hard to pinpoint what is going on without diving deep into your car’s internal system.
From bent piston rods that transmit power throughout the engine to clogged hoses to burned engine valves that help fluid flow, you’ll want to take your car to a mechanic to diagnose deeper issues that might be causing your car to backfire.
What to do when a car backfires
Backfires can happen at the engine or muffler. Additionally, the type of sound the backfire emitted—a loud pop or a gurgle—can hint at the type of problem you’re encountering.
Check your engine light
The
check engine light
is typically a yellow, amber, or orange light in the shape of an engine or jagged rectangle. Sometimes the word ‘check’ will directly be under the engine symbol. If your check engine light is on, the car engine will reduce its power to mitigate further damage. The light can be on for several reasons—a worn-out spark plug, defective airflow and
oxygen sensors
, or a loose gas cap
, among other things. While this light doesn’t necessarily signify an emergency, it is serious. You should head to the mechanic as soon as possible for a proper diagnosis.
Let your engine rest and listen
A backfire isn’t always explosive—sometimes, it can sound like a low gurgle. If your car emitted this sound, turn the car off, and let the engine rest.
While you wait for the engine to cool down, take a look under the hood for tattered wires and disconnected hoses. You may be able to fix the problem yourself once you reach home. If you’re in doubt, it’s always best to take your car to a repair shop or mobile mechanic.
Backfires can also sound like hissing or sucking noises. These sounds point to a leak in the exhaust. If the sound persists, book an appointment with a mechanic right away. Leaving mechanical issues undiagnosed can lead to a dramatic decrease in your car’s performance—and usually higher repair costs.
MORE: How to know if your mechanic is taking too long with car repairs
How to find affordable car insurance
Once your car is fixed and ready to go, take a few minutes to revisit your car insurance and make sure you’re fully protected.
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4.7/5 rating on the App Store | Trusted by 5+ million customers and 7 million cars4.7/5 app rating | Trusted by 5M+ driversIs it illegal for a car to backfire?
Unexpected backfires are not illegal but do require mechanical repair. However, it is illegal to modify your exhaust system that has already been approved according to industry standards. You can be fined for disrupting noise level laws in your area, so best to steer clear of sounding the alarm with loud backfires.
Why do souped-up cars backfire?
A badly timed engine, dirty air or fuel filters, leaky exhaust, or an older car engine can contribute to a car backfiring. All backfires are not the same, so you should visit a mechanic to help you find the right solution.
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