Engine misfires are a common issue, and if one occurs, you might wonder if it will damage your engine. Is it safe to drive with a misfiring engine? What brought it about in the first place?
Most of the time, if a strange sound from your car occurs just once or twice and then vanishes, we’re content to ignore it. However, it’s in your best interest to comprehend why an engine misfires and what, if anything, you can do to prevent it.
If ignored, engine misfires can become a very serious issue. They not only significantly lower your car’s performance but also run the risk of costing you a lot of money and ruining your engine.
If a misfire only occurs occasionally, it may be tempting to ignore it. Nobody wants to have to take their car to the mechanic because it’s a hassle and you know it will end up costing you money.
But the longer you wait to find out what’s causing an engine misfire, the worse things could get. Finding the cause of the problem as soon as you can saves you time and money.
But it’s best to understand exactly what a misfire is and why it might have happened in the first place before you do any of that. The first step in solving a problem is to recognize it.
A Misfire In an Engine: What Is It?
Gasoline mixed in exact amounts with oxygen in your engine powers your car. The motion energy is produced by combustion, which takes place in the cylinder and causes the pistons to pump up and down.
For the engine to function properly, every cylinder must fire in an extremely precise order, one after the other. That incorrect timing of the combustion reaction results in an engine that misfires.
The 4 to 12 cylinders are the usual range for an engine. More is possible; some extremely fast cars even have 16 cylinders. However, 4-, 6-, and 8-cylinder engines are the most popular.
A power loss proportional to the cylinder dropping out of the entire combustion reaction occurs when one of your cylinders misfires. In a 4-cylinder engine, this means that you would lose 25% of your power if one of the cylinders failed to fire.
What Causes a Misfire In an Engine?
Several issues, as opposed to some engine-related issues, can result in engine misfires. Some are more typical than others, and some require more money to fix.
1. Malfunctioning Spark Plugs
A defective spark plug might be to blame for a misfire. The spark that ignites the mixture of fuel and oxygen in the engine comes from spark plugs. Therefore, the engine misfires if your spark plug doesn’t spark properly because there isn’t anything to ignite the fuel/air mixture. Corrosion or poor wiring could be to blame for a bad spark plug that isn’t functioning properly.
2. A Defective Ignition Coil
An engine misfire could also result from the ignition coil failing. A spark plug’s ignition coil transforms the battery’s 12-volt power into the much higher voltage required to start the combustion reaction. A malfunctioning ignition coil won’t be able to properly convert the voltage, which could result in a misfire.
3. A Defective Fuel Injector
An improper fuel/air mixture can also lead to an engine misfire. A malfunctioning fuel injector or even an air leak somewhere along the line may be to blame for this. However, faulty fuel injectors will result in misfiring on all cylinders as opposed to just one.
4. A Vacuum Leakage
You may also experience engine misfires if the vacuum system surrounding the intake manifold of your engine malfunctions. You get a very lean fuel mixture in the cylinder when the vacuum leaks, and if it’s too lean to ignite, you get that misfire.
5. Damaged Piston Rings
Piston ring wear is one of the more serious factors in the engine misfiring. Damaged piston rings are unable to adequately seal the cylinder. This may result in frequent misfires and fuel leaking from the chamber. The cost of fixing this issue may be very high.
What Damages Can Be Caused By a Misfiring Engine?
Driving with a cylinder misfire can harm your engine in many different ways. Over time, it will harm the pistons and cylinders, but the catalytic converter will experience damage first.
The fuel entering the combustion chamber is not burning when your engine misfires. As a result, unburned fuel will enter your catalytic converters, increasing the heat and risking damage to the converters as your engine continues to struggle to operate.
Because your engine is operating too leanly, you must be concerned about heat damage to the engine over time. The pistons and valves are not made to withstand high heat for an extended period. Even the valves or cylinder head may eventually warp or crack as a result of that intense, prolonged heat.
Your engine will be saturated with extra fuel if it is running too richly. As a result, the lubrication on the cylinder walls will deteriorate, which over time may also cause damage. There is never a circumstance where allowing an engine to continue misfiring won’t result in more harm.
How Much Does an Engine Misfire Repair Cost?
Misfires are never enjoyable to deal with, especially when the cost of repairing the damage is involved. Nevertheless, it’s risky to drive with a damaged cylinder, so get your car checked out and fixed before you get back on the road.
Depending on the cause of the misfire, the cost of repair and replacement can range from $100 to $1000. The following is a list of the most typical misfire causes and an estimate of their typical repair costs:
1. $200 to $1,000 for a Malfunctioning Fuel Delivery
The actual cost of replacing a fuel pump is influenced by several variables. Depending on the vehicle, a fuel pump’s parts price ranges between $75 and $250. Beyond this, the cost of replacing the fuel pump yourself is simply your time. A fuel pump replacement is typically regarded as an intermediate-level task.
If you choose to hire a professional, you might expect to pay between $400 and $600 for labor to replace a bad fuel pump. To find a mechanic who can assist with the fuel pump repair in your area, search through the Preferred Shops in your neighborhood.
Depending on the mechanic’s experience and the tools they happen to have on hand, you can anticipate the actual replacement to take anywhere from one to six hours.
Make sure the fuel tank is thoroughly cleaned of all contaminants, whether you do the work yourself or hire a professional to do it. Years’ worth of fuel sediment can accumulate in the fuel tank’s bottom. If you decide to do it yourself, keep in mind that you can buy all the tools and parts you need in online auto stores!
Storage and delivery of fuel to the cylinder chamber, where it can be combined with air, vaporized, and burned to produce energy, are the two main duties of the fuel system. A fuel tank holds the fuel, which can be either gasoline or diesel.
Fuel is delivered to the cylinder chamber for combustion by a fuel pump after being drawn from the tank via fuel lines, passing through a fuel filter on the way to either a carburetor or fuel injector. This system may become compromised during an engine misfire and may therefore need to be repaired.
2. $100 to $300 for Faulty Spark Plug Wires
The price of the parts and the additional cost of a mechanic’s labor must both be taken into account when calculating the cost to replace spark plugs and wires.
You’ll pay between $123 and $151 for the parts, and an additional $67–$84 for labor.
Therefore, the cost to replace the spark plugs and wires are much higher if you take it to a mechanic and ranges from $190 to $235.
Even though the peace of mind a mechanic can provide for a job well done is undoubtedly priceless, you can try doing it yourself if the additional labor cost is out of your price range. You’ll only have to pay for the parts in this case. This should help you understand how much money you can save by handling repairs yourself.
The air-fuel mixture is ignited in the combustion chamber by spark plugs, but the spark must originate from somewhere. It takes a lot of effort for spark plug wires to transfer electrical charge from an ignition coil to the spark plugs in your car. Spark plug wires deteriorate due to the excessive heat and electricity they encounter.
Replacement is typically advised at intervals of 100,000 to 160,000 kilometers, though replacement may be necessary sooner in difficult operating conditions.
The ignition coil in your car transforms the 12 volts of power from your battery into a high-voltage pulse of about 25,000 volts. The high-voltage charge must be transported to the spark plug without experiencing any resistance-related loss. Spark plug wires are specifically made to do that.
The conducting wires are covered with a thick layer of the shielding material and a silicone or rubber protective cover. This stops the high-voltage charge from arcing to a grounded area, which would drain the spark’s energy.
Each spark plug wire has two ends, one of which is attached to the ignition coil and the other to the spark plug. Each spark plug has a single spark plug wire. Spark plug wires that are cracked or the insulation that has aged due to engine heat should be replaced.
3. $1,000 to $5,000 for Malfunctioning Piston Rings
The price of a new piston ring ranges from $1000 to $5000, depending on the car’s model and labor costs. Depending on how many cylinders your car has, the piston rings can cost anywhere from $40 to $200. The labor costs range from $1000 to $4000.
Despite their diminutive size, piston rings are expensive to replace. Depending on the make and model of your car, you could spend anywhere between $40 and $200 on just the piston rings. Wait until you factor in the cost of labor to see how much that is.
The mechanic must disassemble the engine and reach inside to remove the old piston rings and install the new ones because the piston rings are situated deep inside the engine. This entire process requires patience and accuracy.
The engine needs to be put back together and placed in its position after the new piston rings have been installed. Your mechanic would need at least 16 hours to finish the job. A licensed mechanic will most likely complete the task more quickly and correctly.
You must measure the ring cap and fit the piston rings in the proper order if you want them to be installed correctly. Before putting in the new piston rings, you must also measure and inspect the cylinder walls for wear.
Depending on the engine, the labor cost for a proper piston ring replacement ranges from $1000 to $4000.
However, you can replace them fairly cheaply if you know how to do it yourself. However, be ready for a big job that will require a lot of knowledge.
While disassembling the engine, you might also need to replace other components and even redo the engine block.
The combustion chamber, also known as the space inside each cylinder, is kept under pressure by the piston rings, which makes it simple for combustion to occur.
The piston rings serve as the seal between the piston and the cylinder walls to maintain the crankcase’s oil level and combustion chamber pressure. Your car’s engine will begin to lose power if the piston rings degrade or fail, and if they are not repaired right away, a myriad of other issues could develop.
4. $900 to $1,800 for Damaged Valve Springs
Depending on the make and model of your car, this replacement job will cost between $900 and $1,800. The entire engine must be disassembled to access the valve spring for the process of replacing valve seals. Pull out the pushrods, rocker arms, spark plugs, and cylinder head cover.
One of the more serious causes of engine misfiring is piston ring wear. Piston rings that have been damaged can’t properly seal the cylinder.
As engine speed rises, weak valve springs frequently result in misfiring and a loss of power. The engine can start, idle smoothly, or run normally up to 3500 to 4000 RPM.
Never swap out a single valve spring. Your engine may experience additional issues if you replace a single-valve spring.
The labor should take between 5 and 6 hours per engine to remove the exhaust and valve covers, change the springs, retainers, seals, and locks, adjust the valves, and replace the covers and exhaust. A twin engine should require 20 to 24 hours of labor in total, plus parts.
It is recommended to check the spring pressures once a year or every 15000 miles. They won’t need to be replaced if they are properly maintained. Some springs, when installed correctly, can last for more than 30k.
One of an engine’s most crucial yet underutilized components, the valve spring is an integral part of the valve train. Until the cam opens the valve, which releases pressure, the valve spring keeps the valves tightly closed against their seats. The valve will then be released, giving the valve spring time to do its job before the cam retracts the valve back into the head.
The two primary types of valve springs are single and dual designs, and there are numerous variations of each. The single spring supports the valve solely; the dual has a second, smaller spring inserted inside the first.
The amount of pressure that each valve spring applies to the cam and valve is the other major distinction between them. It’s crucial to select a valve with the proper spring pressure to make sure that it retracts quickly enough, that you don’t experience “valve float,” and that you don’t go too stiff and cause the cam to wear out quickly.
The valve also has keepers and retainers as additional components. Their responsibility is to maintain the valve spring’s tight connection to the valve.
5. $200 to $300 for Oil-Fouled Spark Plugs
Your mechanic can determine the root cause of a damaging, dangerous oil leak that, in some extreme cases, could result in an engine fire by performing an oil leaking into spark plug well inspection.
Oil may be leaking into your spark plug wells if you can smell burning oil while driving, your exhaust is emitting blue smoke, your engine is running rough, or your engine is misfiring.
Fuel and air are mixed in the cylinders of your engine. Afterward, spark plugs use an electrical spark to ignite that mixture, resulting in a small, controlled explosion that forces the pistons downward and produces power.
All of these engine components require motor oil to function properly, and spark plugs are required to ignite the fuel-air mixture. However, you don’t want engine oil to leak into the spark plug wells because this can lead to a variety of problems, including an engine fire.
The typical cost of these repairs is between $200 and $300. Rarely, expensive engine repairs could run into the thousands.
This inspection, which mechanics frequently charge as an “oil is leaking into spark plug well inspection,” aids your mechanic in determining the source of a damaging, dangerous oil leak that, in some rare circumstances, could ignite an engine fire.
A blown O-ring, a tiny, inexpensive gasket that makes an airtight seal in your engine, is usually the cause of oil leaking into the spark plug well. Typically, these repairs cost between $100 and $200.
Another frequent cause of these problems is worn-out valve cover gaskets. These repairs cost about the same, typically between $100 and $300.
A set of spark plug wires by Saen1978 / CC BY-SA 2.5. Spark plug wires have to work very hard to transfer electrical charge from an ignition coil to your car’s spark plugs. The excessive heat and electricity that spark plug wires are exposed cause them to deteriorate.
However, there are more pricey possible repairs. It can also be very expensive to need a new piston compression ring. Although it’s less common, depending on the car, these repairs can cost anywhere from $1,000 to $5,000.
Your mechanic will initially check the engine’s exterior for leaks and check the O-ring seals and valve cover gaskets. The mechanic will also examine the pistons if necessary. To offer more hints, they might need to give the car a test drive.
Your mechanic ought to be able to identify the issue and make the necessary repairs once they have this information. These are fairly typical problems, particularly in older vehicles, so a skilled mechanic should be able to find the issue fairly quickly.
If your vehicle displays any of these signs, you need to stop as soon as it’s secure to do so, turn it off, and make a mechanic appointment. Your engine may suffer a variety of damages from these leaks, and they run the risk of catching fire.
A mechanic will let you know if it’s safe to drive to their shop or if it would be safer to have your car towed after you’ve explained the problem to them.
Long-distance driving may necessitate the purchase of an entirely new engine due to oil leaks and oil pressure problems. Additionally, that is significantly more expensive than buying a new O-ring or valve cover gasket.
6. $60 to $350 for a Defective Ignition Coil
If it turns out that your ignition coils need to be replaced, that should be your top priority.
The cost of replacement depends on the make and model of the car, just like it does with almost any other auto component. Since different cars use various types of ignition coils, there may be even more variation when it comes to these components.
Coil-On-Plug and Coil-Near-Plug ignition coils are the two most popular varieties. In contemporary cars, the Coil-On-Plug is more prevalent than the two.
Depending on the car model and labor costs, the average cost to replace a single ignition coil ranges from $60 to $350. An ignition coil can cost anywhere from $30 to $150. An ignition coil requires labor that ranges from $30 to $200.
In many cases, replacing an ignition coil is fairly simple and you can do it yourself. However, depending on the car model, the process can take an hour or more, so in some cases, you should expect to pay quite a high replacement cost.
Although changing the ignition coil is frequently simple, if you don’t feel confident doing it yourself, take your car to a mechanic and let them handle it.
The spark plugs are intended to receive a high voltage from the car battery via the ignition system. The spark plug will ignite the fuel-air mixture and start the engine with this voltage.
The ignition coil converts voltage from the car’s 12-volt battery to the 25–30,000 volts the spark plug requires to ignite. It is a high voltage, low current transformer.
A BMW M20 straight-six engine by Kether83 / CC BY 2.5. When your engine misfires, the fuel entering the combustion chamber is not burning. Unburned fuel will consequently enter your catalytic converters, raising the temperature and raising the possibility of damage.
7. $200 to $1,000 for a Vacuum Leak
If you’re not very familiar with exactly what happens under the hood of your car, hearing about a vacuum leak in a car might be confusing. The vacuum that most people think of when they think of a car doesn’t exist.
The system that exists between the engine and the mass airflow sensor, which regulates the flow of air through your engine, is what a vacuum leak refers to. Your vacuum system’s repair costs can range from $200 to $1,000 depending on where the leak is located.
As you are aware, to maintain a combustion reaction, your engine needs both fuel and oxygen. A spark ignites the mixture of fuel and air that is injected into the combustion chamber, starting the combustion reaction that powers the entire vehicle.
Similar to how fuel flows through a fuel system, this air must move through the vacuum system in a very controlled and precise manner. Therefore, if the vacuum system develops a leak, you’ll need to have it fixed or you risk experiencing performance issues as a result of poor airflow.
The vacuum system in your car has many different parts, so the cost of repairs can vary widely. It won’t wear out the way a brake pad or a camshaft position sensor will.
Anywhere in your car, including the EGR valve, the positive crankcase ventilation system, the intake manifold, and beyond, could leak. To determine the type of repair you will have to pay for, you must first determine where the leak is.
The air-fuel mixture that powers your car passes through the vacuum system on its way to the engine. Any leak between the mass airflow sensor and the engine is considered to be a system leak.
A leak in the vacuum can affect this because the computer in your car, known as the ECU or the PCM depending on your make and model, determines how much fuel to inject as well as how much air is required. Leaks can result in the combustion chamber receiving either too little or too much air.
This usually results in burning what is known as a lean mixture because your computer is unable to accurately determine how much fuel is required. This indicates that you have more air than you need and insufficient fuel.
Is Driving with a Misfiring Engine Safe?
In a strict sense, driving a car with a misfiring engine is unsafe. You should visit a mechanic as soon as you can if you experience sporadic power loss or poor acceleration. The risks of carrying on with a misfiring engine while driving are numerous.
In congested areas, the lack of power and acceleration brought on by a misfiring engine could be extremely dangerous. That is no longer an option if you need to act quickly to prevent an accident. Consider what would happen if you needed to avoid an approaching vehicle but had very little room to accelerate.
The likelihood that the engine will sustain additional damage increases the longer you drive with a misfiring engine. The stress could make the issue worsen and lead to additional cylinders firing incorrectly until the engine stops working altogether. If you are far from home, such as on a highway or while off-roading, this could be especially dangerous.
You might be tempted to keep going if your engine misfires on and off but the power losses don’t last. However, you don’t want to let go of it for a long time.
A single-engine misfire in a newer vehicle might be enough to put it into limp mode. That is a limited functionality mode of operation controlled by the computer in your car. It is comparable to your computer’s safe mode. The idea is that most systems are safeguarded and that you are capable of driving yourself to a mechanic to have the problem fixed before it worsens.
You shouldn’t put off getting your car fixed if it enters limp mode. Simply put, until you get it checked out, you won’t have the full range of motion that you’re used to.
Avoid letting a misfiring engine continue for too long without having a mechanic examine it. The best course of action is to visit a mechanic if you’re unsure of your capacity to identify and fix the issue.
As you can see, there are a lot of possible reasons why an engine might misfire. If you try to solve this issue on your own, you might end up doing even more harm. If you leave this problem unfixed for a long enough period, your car could sustain severe damage.
When you could have repaired a spark plug a few months ago for around $100, you don’t want to end up having to pay $3,000 to repair damaged pistons.
Jim Wicks is the founder of MotorVehicleHQ. With over two decades of experience in the automotive industry and a degree in Automotive Technology, Jim is a certified car expert who has worked in various roles ranging from a mechanic, car dealership manager, to a racing car driver. He has owned more than 20 cars over the past 15 years. Ask him about any vehicle you see on the road and he can tell you the make, model and year. He loves the aesthetics of all things cars, and keeps his vehicles in pristine condition.
In his free time, Jim enjoys getting his hands dirty under the hood of a classic car or taking long drives along the country roads. His favorite car? A 1967 Shelby GT500, a true classic that, according to Jim, “represents the pure essence of American muscle.”