If you’ve ever been in a vehicle or walking along a busy street and heard a sound similar to a gunshot, and it wasn’t actually a gunshot, you probably heard a car backfiring.
It could be a single pop, a series of pops, and possibly a crackle, or a string of pops in rapid succession if you are hanging out at the dragstrip watching tuner cars.
Some people may think a backfire is cool, but a backfire is really signifying something along the lines that you have a problem with your car. Here is what causes backfires to happen and what type of damage could occur after a long period of time.
What is Backfire?
Backfire happens when unburnt fuel gets hot enough to ignite AFTER the exhaust system, which creates an explosion somewhere other than within your engine.
This explosion is what creates that impressive popping sound when you accelerate, decelerate, or when you are starting up your car for the first time on a cold morning.
However, when that burst of fuel gets too hot, it will explode just like a Molotov cocktail and can even create flames that shoot out the back of your car. (Please, kids; no burnouts next to a field during a fire ban)
What is Backfire In a Car?
A backfire or afterburn is an explosion that happens outside the combustion chamber but inside the exhaust system of a running internal combustion engine.
It is also sometimes called an afterfire, if someone is using the word backfire in the sense of a fuel-burning while an intake valve is open, and it is now moving backward through the system, and now goes out the intake.
When the flame is moving backward, it may also be referred to as a “pop-back”. Backfire happens when either the combustion causes ignition, either with an exhaust valve open, or unburnt fuel has entered the hot exhaust system.
Flames may be visible coming out of the exhaust pipe for a moment! A backfire is usually indicative of an improperly tuned engine.
What Does it Sound Like?
Backfires sound a bit like gunshots, with maybe a bit of fireworks added too. A good backfire is like fine wine… it should be loud, but not loud enough to blow your buddy’s eardrums out.
If you are working on tuning your car for backfires, you might have just a little more fuel than is needed for normal combustion, so excess fuel gets thrown out the back of your exhaust system.
You will want just a little bit of burble as you let off the accelerator, causing the RPM to drop, but still allowing unburnt fuel to flow through the exhaust system. This will leave your heart with the amazing feeling of *burbles* that you can hear from the driver’s seat.
One amazing thing about backfires is that if it is nighttime, you can even watch fire shoot out of the back of your exhaust system.
Why do Car Engines Backfire?
If an engine has too much fuel, then not all of the fuel can burn up before the exhaust valves open. The unburned gasoline enters the red-hot exhaust headers and can combust, which will create a backfire. Too much fuel can be allowed to enter your engine for reasons such as leaky or damaged fuel injectors or faulty engine sensors.
The common causes of backfire are running rich (too much fuel going into the cylinders) and faulty ignition components like spark plugs, coils, or wires, possibly fouled (dirty) spark plugs.
#1. Ignition Timing Problems.
Ideally, your spark plugs should fire only when both valves are closed so the most efficient burn occurs. If the ignition timing is off, then you would burn your fuel when one of the valves is still open or closing, and you’ll have a disproportionate amount of fuel sent through the exhaust system.
If you have enough unburned fuel pushed through too many hot headers, you can ignite it, and get an explosion to pop through the exhaust system.
#2. Lean Air/Fuel Mixture.
If the clogged fuel injectors, dirty fuel filter, and/or failing fuel pump, which is usually the case. You’ll most likely have a “lean air/fuel mixture” in the combustion cycle. And by “lean,” I mean there is not enough air to burn all of the fuel in time for a proper combustion cycle.
It is all about the balance of air, spark, and fuel. If one is in any way short, the engine will throw a Check Engine Light, and you’ll have too much unburned fuel exiting through the exhaust system.
#3. Rich Air/Fuel Mixture.
When you have a lot of fuel, then the air/fuel mixture is considered to be “rich.” You want to have the best combustion possible, so you must have the perfect air-to-fuel ratio.
If you can maintain this, then you will not only prolong the life of your engine, but it will also cost you less in the long run.
If you’re rich in the ratio, you send too much fuel into the cylinder, which then will create an incomplete burn.
And like everything explained above, you are now sending too much fuel unburned out the exhaust valve. The unburned fuel will ignite in your exhaust, which will create a loud *pop* noticeable from your driver’s seat.
When the pop occurs, you are now creating a break in the exhaust flow, and so you have a momentary lapse in acceleration, which you will most definitely feel. Your car will feel sluggish, and you will not street race well. Remember, a good engine is smooth, and a smooth engine is a fast engine.
#4. Bent or Damaged Valve.
Most cylinders will have at least one intake and one exhaust valve. These intake valves will open and close to allow air and fuel in, while the exhaust valves will open at the end of each combustion cycle to expel all of the emissions/excess gas and fuel.
Like most moving parts in your vehicle, the valves are designed to create a good seal when closed to ensure the most efficient combustion cycle possible.
So, if the seal wears out or the valves bend, it will no longer seal the entrance to the cylinder, preventing fuel from going in when you’re not supposed to.
If you have too much fuel going into the cylinder during compression, you will have an excess of unburned fuel in your exhaust gases.
This amount of unburned fuel may be irregular due to bent valves, unlike a “rich” air/fuel mixture, which is a predetermined amount based on fuel injector and ignition timing.
Fortunately for you, the backfire that you may be experiencing is probably not from bent valves, or at least this will be a costly repair from your local mechanic.
Also, bent valves tend to arise from an engine timing error, causing the engine timing belt or chain to break before the bent valves cause a backfire.
#5. Incorrect Spark Firing Order.
With the advent of electronically controlled engines using a coil-on-plug ignition system, this problem is virtually gone. However, on older models with spark distributors and spark plug wires, it is possible to accidentally add the spark plug wires to the spark distributor in the wrong order.
If the spark fires in the wrong cylinder, at the wrong time, this is guaranteed to create a backfire, among other problems! This same problem can happen if the spark plug wires cross after having your spark plugs changed. Again, most modern cars have engineered this problem out of existence.
Why Do Cars Backfire When Shifting?
Backfiring can occur not only while your engine is starting, but sometimes it can happen when you shift your car, such as when you change your shift. That loud pop during the shifting process is actually called an afterfire.
Afterfires predominantly happen in a manual transmission since you are using a clutch to shift gears. When you press in your clutch and release from one gear while transitioning to the next gear, fuel can also still enter the cylinders, especially if you are shifting at higher RPMs.
All this unburnt fuel piles up in the exhaust and ignites when you release the clutch. While this can seem alarming when it occurs, typically, after a backfire is the loud “pop” during a shift is not damaging to your car.
Is Backfire Bad for a Car?
With any vehicle, anything outside of the manufacturer’s specifications is generally going to decrease the life span of your powertrain, suspension, and reliability.
Backfire will essentially reduce your fuel economy, which means you cannot go where you want to go without then spending more money on gas.
Unfortunately, backfire can also cause damage to your catalytic converters and will also cause you to lose power.
Your catalytic converter has damage because all that unburnt fuel is now going to be burning up your “cat”, instead of burning up inside the cylinder walls where it is supposed to burn.
Because catalytic converter theft has been on the rise, new catalytic converter prices have recently taken a rise across the US. Therefore, you will want to take as best care of this component as you can.
If you have excessive backfiring upon acceleration, your engine will think that there is something wrong (there usually is) and start to dial back your engine’s power.
This is a failsafe mechanism; your car’s ECU is going to take precautions due to excessive backfire damage.
If you have fixed the issue (the cause) behind your backfire, and want to reset your car’s ECU.
Is Backfiring A Car Illegal?
Backfiring on a car is not illegal if by accident. And besides, in most cases, you didn’t do anything wrong, and you’re just trying to get to work.
Now, if you have your car back-firing loudly or excessively because you want it to, and you’re disturbing folks, the police may look a little closer.
If your car runs too rich, diminish the catalytic converters and will no longer pass emissions, then you will have an illegal car.
How To Make Your Car Backfire?
If you’ve made it to this point in the article, you are most likely a car enthusiast who wants to backfire their car, and let’s face it, who doesn’t wanna shoot flames and make a ton of noise when driving their car.
In an older car, you will need to warm up the engine, then let it sit for a minute or two, and turn your key off.
With your foot on the accelerator and the brake, of course, start up your car, and give it a good rev, you should hear a bit of popping as the car tries to master the air/fuel mixture.
Another method of getting your car to backfire is accelerating to 60mph or so, and then decelerating via the engine, simply by shifting down one gear lower than the gear you’re in, then letting the engine and transmission slow you down. If you listen carefully, the exhaust systems should make some burbles and pops.
Now, the last and most fun way to backfire a car is to purchase a proper performance exhaust system suitable to support back-firing, and with an ECU tune to allow for a leaner/fuller fuel/air mixture, you control how much backfire your vehicle produces while doing normal driving!