Finding out the cause of an engine misfire can be tough, but context can be a big part of the hint.
Misfires can be intermittent and even sometimes only show up in a specific fuel, environment, or engine load (engine load refers to how far you’re in the gas pedal).
Don’t ignore engine misfire symptoms because a misfiring cylinder increases the strain on the engine and fuel economy over time. These are the most common engine misfire symptoms.
What Is an Engine Misfire?
A healthy four-stroke combustion engine executes all the necessary functions in the proper timing and order to burn fuel and create power.
- As the piston travels downward, a specific air-fuel mixture enters the combustion chamber as the intake valves open. After the valves close, the air-fuel mixture is compressed as the piston travels upward.
- The ignition system fires the spark plug during the power stroke, igniting the air-fuel mixture and increasing the cylinder pressure. With cylinder pressure, the piston is forced downward quickly while rotating the crankshaft at the same time.
- The exhaust valves open during the exhaust stroke, and burnt gases are expelled from the cylinder.
The whole timing and sequencing must occur to avoid misfire. Misfires are caused by a failure of combustion, which can come from any of the components necessary for combustion (fuel, oxygen, and spark) or the mechanical components themselves, such as the cylinder itself.
Misfire can be caused by one of two main reasons: an incorrect timing sequence or one of the cylinders fails to complete all steps of the cycle. If there is an incorrect air-fuel ratio, the mixture may not combust or may prematurely detonate (knock).
What Does a Misfire Feel Like?
From the driver’s seat, a misfire feels like coughing or stumbling occurring under the hood. The engine is failing to operate in a methodical and rhythmic fashion, and those in the cabin feel it in real time.
A misfire can occur at idle, when driving down the road at a steady speed, and when accelerating or braking, but typically occurs under what’s called load, which means the car is accelerating down the road with the use of its engine power.
When a vehicle is accelerating, it needs the most fuel, air, and spark, depending on the amount of acceleration needed. If fuel, air, or spark is limited, then a misfire will be most apparent under acceleration.
Misfires under load may also lead to poor or no acceleration, which can become a safety concern out on the road. Misfires should be addressed as soon as possible.
Reasons why your Engine Misfires
#1. Spark Plug Faults.
Worn or malfunctioning spark plugs are a primary cause of engine misfires. Spark plugs can wear down over time or can become covered in carbon deposits, which will lead to weak and inconsistent spark production.
If your engine cylinders aren’t firing completely, the result is misfires and decreased engine performance. You should regularly inspect and replace spark plugs in your engine to ensure peak performance.
#2. Ignition System Malfunctions.
In addition to spark plugs, the ignition components aiding in the production of sparks in the cylinders include the ignition coil, wires, and distributor.
If any of those components fail to work properly or are damaged, it may not deliver a spark to the engine cylinders used to ignite fuel, which would cause misfires.
Bad ignition coils, broken wires, and corroded connectors are a few of the ignition component issues that would need to be correctly diagnosed and repaired to fix misfires if discovered.
#3. Fuel System Issues.
Fuel system issues can also cause engine misfires. If a fuel injector is clogged, you have low fuel pressure or a dirty fuel filter, the engine cylinders aren’t getting the correct fuel delivery needed to operate efficiently, so it can misfire.
If you have contaminated fuel or a faulty fuel pump, it could create issues with fuel combustion and, ultimately, problems with the engine performance. A dirty fuel system needs regular maintenance and should be cleaned periodically to prevent misfire-related issues.
#4. Air intake and vacuum leaks.
If there are leaks at the intake manifold or a vacuum hose, they can disrupt the air-fuel mixture entering the engine and cause misfires. If there is an air leak, it will cause unmetered air to enter the combustion chambers and create an imbalance of the air-fuel ratio in the engine.
A leaking air intake system should be inspected, diagnosed, repaired, and tested to fix a misfire condition and return engine performance to its best.
Common Symptoms of an Engine Misfire
Engine misfires can, just like any other problem with the vehicle, have the same symptoms as other issues. The first step in diagnosing a problem is to check the vehicle’s computer for trouble codes.
If you experience any or multiple of these symptoms, you should be suspicious of a misfire.
#1. You are losing power, stumbling, or vibrating.
You may wonder, “What does a misfire feel like?” You may genuinely feel a loss of power, either because the vehicle is running on fewer cylinders than it should, or there is a short hesitation before power is applied when you step on the gas.
There may also be the feeling of intermittent jerking, bucking, or stumbling of the engine. You will notice rough and/or slow acceleration.
You will feel vibration while the vehicle is also running itself (and especially if the misfire is caused by a mechanical problem). The severity of the vibration is dictated by the RPM, but is often worse while the vehicle is at idle.
#2. Abnormal Sounds.
So what does a misfire sound like? During a misfire, the engine will make a quick sound that you might describe as popping, sneezing, or backfiring.
Backfiring occurs when unburned fuel exits the cylinder on the exhaust stroke, and this unburned fuel is later ignited by the spark plug of the next cylinder.
One way to tell if an engine is misfiring is if you hear a noticeable change in the engine sound; a misfire is one less firing cylinder. It’s the same as if a spark plug just blew out of the cylinder head.
In addition, you may hear a sound like a vacuum leak as well in the engine.
#3. Unusual Smells.
A misfire can also create unusual smells since the fuel-air mixture has not completely combusted. Depending on the scenario, when a cylinder misfires, the unburnt fuel could be dumped into the exhaust system and could produce a strong gasoline smell.
In addition, it could send the unburned fuel into the exhaust system, and if that hits the catalytic converter, excess unburned fuel could overload it and cause sulfur or even rotten egg smells as it tries to burn all the hydrocarbons.
#4. Check Engine Light.
After 1995, all vehicles started being pretty much standard with OBD2 systems to help diagnose issues with the engine. When any of the vehicle’s sensors see readings that fall outside some expected range, the vehicle will illuminate a check engine light and store a code in the engine control unit (ECU).
Most OBD2 vehicles will have a code for “Cylinder X Misfire” type code that will help you with a starting point for locating your problem (where X is the cylinder that misfired).
Sometimes the check engine light will stay on until it is cleared; in some vehicles, the light will flash during the misfire. The check engine light can be triggered by a multitude of different causes, so it is necessary to have the code read to see exactly what happened.
Common diagnostic trouble codes P0301-P0312 will appear. The last two digits indicate which cylinder had the misfire. For example, P0306 indicates a cylinder 6 misfire.
However, the code P0300 can also show up because it relates to multiple cylinders misfiring.
Many automotive stores, such as Auto Zone, will do this for free. Write down the code and the description of the problem for troubleshooting.
#5. Struggling Engine.
When multiple cylinders misfire and disrupt the engine process, this tends to disrupt the power output, so it’s not smooth or consistent.
When one cylinder does not fire as expected (or more than one), the resulting power output of the engine is now out of balance. When this happens, the engine may struggle or shake when trying to gain momentum or to maintain a certain speed up a hill or incline.
You may even notice jerky motions when the vehicle is accelerating, or just a noticeable loss in power as the engine doesn’t have the level of performance you are used to.
It is most noticeable when the engine is under load (as stated above), where all cylinders must work efficiently in order to continue going forward and maintain speed.
Additionally, misfires can lead to an engine that is hard to start when starting the vehicle or even engine stalling when coming to a stop. An engine stall is more likely to happen with a high accessory load (e.g., air conditioning, headlights, and even radio).
#6. Excessive Exhaust Smoke.
If you see black, blue-tinted, or very white, sweet-smelling exhaust, you have a problem. Dark, sooty exhaust generally means there is a rich air-fuel mixture or carbon build-up, and blue-tinted exhaust generally means oil is burning.
White, sweet-smelling exhaust could mean a head gasket leak. Something in the combustion chamber other than air and gasoline will compromise the vehicle’s ability to burn properly.
Ways to Troubleshoot Engine Misfire
#1. Diagnostic Testing.
Diagnosing engine misfires is critical in determining a vehicle’s malfunction. A professional mechanic will use diagnostic equipment to place a value on the misfires.
The diagnostic tests can include compression tests on cylinders, checking ignition systems, and inspecting the fuel systems. Once we find what is causing the misfire, we can move on to a reasonable area of repair to fix the problem.
#2. Spark Plug Replacement.
If you find that the spark plugs are old and worn-out or fouled, they should be replaced to ensure proper ignition and combustion.
Please be sure to use the proper spark plugs that provide the correct gap settings and type for your vehicle’s engine. Regularly scheduled spark plug maintenance can be beneficial as a preventive measure to help avoid future misfire problems.
#3. Ignition System Repair.
Replacement or repair of an ignition system component that is not working properly will help to resolve mechanical engine problems that could be causing the misfires.
Components needing serious repair include faulty coils, wires, or not working properly distributors. An accurate examination of the ignition system parts should be done thoroughly to provide the proper value of misfires from damaged or worn parts.
#4. Fuel System Repair.
Dirty fuel injectors, dirty filters, or dirty fuel lines can clog fuel delivery and combustion, causing engine misfires. Using good quality fuel (Top Tier program fuels) and additives designed to keep fuel systems clean prevents delivery problems and improves engine performance.
Engine Misfire Effects on a Car
The most common and obvious effects of a misfire are that your car cannot get proper fuel economy.
A misfiring engine can also threaten your well-being driving on the road, which could easily cause an accident when you might not have the power to accelerate to overtake or avoid a road hazard.
Aside from these more immediate dangers, misfiring cylinders can create more significant damage to your engine. Misfires don’t just go away – they need to be fixed immediately. Even if the problem does not worsen, it certainly will not go away if you do not get the vehicle to a mechanic for repairs.
The longer you ignore the condition and try to drive the vehicle during the misfiring condition, there is a longer chance that your engine may incur more severe damage.
A misfire by itself is not usually a sign of a serious mechanical issue, mostly it is limited to just a bad spark plug, ignition coil, or fuel injector that requires replacing.
However, if you choose to ignore the problem, the chances increase that you will have more cylinders not working properly, and possibly to the point where the engine ceases to function completely.
Rather than getting into that situation, it is always best to have your vehicle taken to a mechanic to get the misfire problem resolved as soon as possible.
If you leave the problem of engine misfire unresolved, this can lead to further issues. If unburned fuel is entering the exhaust system, this can ruin a catalytic converter and cause excessive wear of internal engine components by repeated misfire.
The engine heat strain from repeated misfires can lead to engine overheating, thus increasing the risk of catastrophic engine failure.
At the same time, however, the initial issue could be as minor as fuel injector dirt or a worn spark plug. Ignoring a misfire will allow many other cylinders to misfire and lead to engine failure altogether.
Can Misfiring Damage an Engine?
Yes, misfiring will damage an engine, especially if not repaired. Frequent misfires create repeated excess heat and pressure in the combustion chamber, which, over time, destroy critical components.
If left untreated, the catalytic converter can become clogged or fail completely because of unburned fuel. Misfiring can also warp engine components, ruin valves, and cause significant wear to the pistons and cylinders.
And in some cases, serious enough misfiring can even cause the engine to cease or stop.
What starts out as a small problem, like a bad spark plug or sensor fault, can quickly turn into a bigger mechanical problem. The longer you drive with a misfiring engine, the more extensive and expensive the damage will become.
This makes timely action important to get the issue inspected and repaired by a professional technician at your trusted repair shop.
What To Do If Your Vehicle Is Misfiring?
Whether it is just annoying or a safety hazard, an unresolved misfire could cause great harm to the engine in which it misfires, creating a costly repair bill. So, best to address the misfire as soon as it becomes apparent.
A misfire could have an associated feeling of a woosh or bang, when unburnt fuel is ignited when it was not supposed to be.
This type of incorrect fuel ignition not only places tremendous stress on the engine, but this force can also damage the vehicle’s catalytic converter, which is an expensive part to replace, and specifically an emissions component.
At the very least, a misfire will negatively impact drivability, and your fuel economy will suffer. But the cost of a repair can get exponentially higher if it goes on to damage your catalytic converter or oxygen sensor.
The average cost to replace a catalytic converter can range between $300 and $2,500, and again, that is only the parts cost and does not account for the labor cost to repair.
While repairing a misfire does not generally have to be expensive, that is because reasons that do make it an expensive repair, such as engine damage, catalytic converter damage, or oxygen sensor damage, typically start with a misfire.
Most misfires are a result of wear and tear with aged ignition components, which are generally inexpensive and easy to replace. So bottom line is to get the issue resolved sooner rather than later, or consider the risk of potentially damaging a more expensive part of your vehicle.
Fortunately, most misfires turn on the check-engine light, giving you a clear message: something is wrong with your engine. A mechanic who has proper computerized diagnostics equipment can zero in on the details of the issue and how to go about repairing it effectively and efficiently.
Lastly, it makes sense for the car owner to be aware of the overall condition of the vehicle and follow the manufacturer’s recommended service guidelines, especially if they want to avoid misfires in the future.