One of the most annoying situations that you want to avoid is an engine misfire. But regrettably, they will eventually happen in every engine for one cause or another. What does it feel like when an engine misfires? What results in a cylinder misfiring? What signs indicate an engine misfire? Can engine misfires be prevented? And what does it imply for the well-being and safety of your car? All of these inquiries, as well as how to identify an engine misfire, diagnose it, and correct it, will be addressed.
A Misfire In an Engine: What Is It?
It is helpful to first grasp how a gasoline engine produces energy by compressing and igniting an air-fuel mixture to comprehend a misfire.
A series of valves allow air (and fuel in the case of port injection) to sequentially enter each cylinder while the engine is running. The valves close and the piston in that cylinder swings upward to pressurize (compress) the mixture after air and fuel have been drawn into that cylinder.
After then, the air-fuel mixture is ignited by the spark plug. The crankshaft rotates as a result of the explosion (combustion) pushing the piston downward. The procedure is repeated in each cylinder of the engine to provide the rotational force required to move your car forward.
When there is no combustion taking place in one of the engine’s cylinders, there is a misfire. The check engine light will nearly always come on in a modern car when there is a problem. Additionally, you might observe that the engine lags, hesitate, or lacks power (or suffers from all three issues).
Why Does the Car Engine Misfire?
An important first step in solving the issue and preventing engine misfires is understanding their causes. Let’s examine the root reasons for an engine misfiring in more detail.
A V6 internal combustion engine by Till.niermann / CC BY-SA 3.0. Your four-cylinder engine could become a three- or two-cylinder one due to misfiring, which could cause one or more cylinders to stop working entirely. Only people with keen ears can normally hear an engine misfire sound.
1. A Bad Distributor or Ignition Coil
Normally, the ignition coil, distributor, or both should be checked first when you suspect your engine is misfiring. Spark plugs are ignited by distributors in older autos.
There are delicate touch areas inside the distributors. If any of these components were to corrode, wear out, or be damaged, an engine misfire might result.
Some older cars have both distributor and ignition coils in addition to the distributor. When the coils malfunction, the spark plugs or distributor won’t receive the necessary voltage, which causes a misfire.
To prevent serious cylinder misfiring, you must replace the ignition coil and distributors if a thorough diagnosis reveals that they are far past their prime. The majority of more recent vehicles just have ignition coils.
2. Unreliable Spark Plugs
One of the most frequent reasons for a cylinder misfire is a bad spark plug. Remember that the spark that ignites a tiny explosion that moves the piston up and down in the cylinder walls is produced by the spark plug.
Any spark plug that is not working properly or at all could leave too much fuel in the combustion chamber, which would cause an engine to misfire at low rpm.
Spark plugs should be one of the first things you check when you encounter a misfire since they can deteriorate or wear out over time. Given how inexpensive and simple it is to replace them, you should always hope that they are the problem.
3. Faulty Injectors
A poor or “stock-tight” fuel injector may provide the combustion chamber with little to no fuel. Soon, we’ll go through how to identify and swap out subpar fuel injectors.
4. Reduced Fuel Pressure
Low fuel pressure causes an engine to run lean because not enough fuel is going into the cylinder. A misfire will result from that lean fuel combination. Many things could be to blame. The fuel regulator is a great place to start ( if your vehicle is equipped with one). An ineffective or broken fuel pressure regulator will prevent enough fuel pressure from passing.
Your gasoline filter is a different area that needs your attention. To increase the lifespan of the fuel injectors and carburetors, the majority of cars come with a single fuel filter that filters fuel entering the gas tank.
Some vehicles feature an additional filter (making them two filters). Low fuel pressure will result if these filters become clogged with debris and filth that they have been denying access to pass through.
Last but not least, a damaged fuel pump might result in auto misfires during acceleration or while the engine is running hot. You probably have fuel pump problems if you diagnose your automobile and get codes for all cylinder misfiring or random misfiring.
5. Reduced Compression
Low compression is another frequent cause of engine misfiring that you should investigate. Low compression, however, could be caused by numerous circumstances. The timing of the engine should be checked first. Compression and timing problems are frequently caused by a faulty timing belt.
Porsche Formula One engine by Morio / CC BY-SA 4.0. Your car’s performance will suffer if your spark plugs start to malfunction. Watch out to see whether a spark plug is misfiring: sluggish acceleration, poor fuel economy, engine misfiring, and challenging start.
You must first confirm the timing. Using a timing light is the simplest way to check the timing. To locate a timing indicator on your main engine pulley, you must understand how to operate a timing light. If your car uses a distributor, you can change the ignition points and timing by turning the distributor.
6. Leaky Intake Manifold
One of the frequent reasons for engine misfiring is vacuum leakage. Additionally, you should check your intake manifold. The intake manifold is a great spot to start a vacuum leak test. I’ll demonstrate how visually appealing and reasonably priced it is to identify a vacuum leak after I show you how long the passages in this text are.
Engine Misfiring Symptoms
There are a few indicators you should be on the lookout for before we proceed with analyzing your automobile for a misfire.
1. The Check Engine Light
The dashboard warning light will turn on if your car experiences misfiring due to faulty injectors, poor spark plugs, insufficient fuel pressure, or any other reason.
Engine system issues are indicated by the check engine light. The car computer, an electronic module, is a feature of contemporary automobiles. These sensors will alert the computer if any component of the engine begins to malfunction.
The computer will assess the severity of the issue, and if it necessitates immediate care, it will turn on the check engine light to alert the driver.
You must keep in mind that the check light may also be activated by a variety of other circumstances. Once the light appears, you should diagnose your vehicle to determine the true source of the issue.
2. Unsmooth Idle
Even while a triggered check light might not immediately bring to mind a misfire, difficult idling is one telltale indicator of one. A harsh idle might happen for a variety of reasons. It could be caused by defective spark plugs, vacuum leaks, clogged fuel filters, or an engine that is running lean. If the lean running engine is the cause of the harsh idling, it could seriously harm the engine.
3. A Sluggish Acceleration
Your air-fuel mixture ratio will be affected by a misfiring engine. When this occurs, it will communicate erroneous information to other components. The oxygen sensor is one of these parts. The auto computer will limit acceleration if the oxygen sensors transmit inaccurate data as a result of the improper air-fuel ratio.
In automobiles equipped with turbochargers, this symptom will be more obvious. The engine won’t get the necessary air or boost, which will make driving unpleasant.
4. Unsteady Acceleration
Additionally, a misfiring engine may result in a jerky acceleration in your car. You can feel jerking and surging when driving as the engine revs increase during acceleration. The easiest method to identify an engine misfire is when it occurs when you are accelerating.
Honda engine by Morio / CC BY-SA 3.0. A misfire occurs when there is no combustion occurring in one of the engine’s cylinders. Modern cars almost usually have the check engine light on when something is wrong. You might also notice that the engine sputters, hesitates, or lacks power.
5. The Engine Sounds Weird
It could be difficult for you to recognize this sign if you are not an automotive engineer with practical knowledge. The fact is that different engines have distinct noises. V8 engines have a distinctive sound from V6 or 4-cylinder engines.
During misfiring, one or more cylinders may completely stop functioning, turning your four-cylinder engine into a three or two-cylinder one. An engine misfire sound is typically only audible to those with sharp ears.
A significant misfire will be indicated by a different engine sound produced when one or more cylinders are lost. Additionally, this will cause a gradual acceleration. A loss of two cylinders in a V8 engine results in a 25% reduction in engine power.
In contrast, a four-cylinder engine will lose 50% of its power if two of its cylinders are lost. A 4-cylinder engine makes it easier to locate a dead cylinder after a misfire than a V8 engine.
6. Engine Rumbles
To guarantee you have a balanced engine, auto manufacturers go through pricey procedures. That balance is lost when you misfire. While accelerating or idling, you’ll feel your automobile vibrate.
You may check the vibration in your automobile by opening the hood if it is parked on level ground. Depending on how many cylinders in the engine are misfiring, the vibration gets worse.
Why Does a Cylinder Misfire Occur?
In addition to the misfiring engine causes we discussed above, I will give you an overview of what causes cylinder misfires in a gasoline engine. Even if some of these causes may appear typical, you must be on the lookout for them. The misfire may be brought on by a simple fix.
1. Ineffective Valve Cover Seals
Poor valve cover seals are another cause of a misfire. Engine oil leaking into a spark plug tube as a result of a poor or weak seal will result in a misfire. It’s necessary to remove the oil from the plug tubes and swap out the worn-out seals.
You must remove the spark plugs before using a suction tool to remove the oil from the tubes and clean the oil. Take a large screwdriver and a clean rag and get inside the spark plug tubes to clean the oil (the suction tool will only work if there is too much oil inside the tubes). This must be completed one at a time.
2. Water In the Fuel Lines
There’s a good risk that water in the fuel line will enter the combustion chamber and result in a misfire.
3. Faulty PCV Valve
A faulty PCV valve might result in a vacuum leak, which will lead to cylinder misfiring.
4. Spark Plug Tubes with Water
Although it’s uncommon, there’s a chance that water got into places it wasn’t supposed to if you recently had your automobile steam cleaned. The spark plug tubes are a nice illustration. It won’t just result in a misfire; it can also harm your ignition coils.
In addition to the distributor, some older cars also feature ignition coils. Spark plugs or the distributor won’t receive the required voltage if the coils aren’t functioning properly, which results in a misfire.
What Is the Relationship Between Spark Plugs and Engine Misfire?
There won’t be anything to ignite the gasoline in the combustion chamber if the spark plugs aren’t working. A combustion engine’s spark plugs are a crucial component.
Spark plugs work by transmitting an electrical signal from a distributor or ignition coil at a predetermined moment to produce sparks that ignite the air-fuel combination in the combustion chamber.
With a defined spark plug gap set by manufacturers during installation, each car needs a distinct set of spark plugs. Poor spark plugs may not light at all, while good spark plugs will ignite quickly.
To keep your engine operating smoothly, spark plugs need to be maintained and replaced, just like air filters, fuel filters, and motor oil.
However, some newer SUVs and trucks with better ignition systems do not require new spark plugs. Spark plugs will occasionally show evidence of wear or failure, despite what auto manufacturers may claim or warranty.
Therefore, your car’s performance will be significantly impacted when your spark plugs become faulty. When determining whether a spark plug is misfiring, keep an eye out for the following symptoms: sluggish acceleration, poor fuel efficiency, engine misfiring, and difficult starting.
Identification and Repair of Engine Misfires
Following our discussion of several engine misfiring reasons, I’ll show you how to resolve engine misfire problems. I suggest taking the actions listed below if you are unsure of what caused the misfire.
1. Retrieve the Error Codes
The car computer ought should be able to provide fault codes if a warning light displays as a result of a misfire. The majority of auto repair shops and parts stores have scan tools that can retrieve and decipher the codes for you. There are also inexpensive code readers available, but you must conduct Google searches to learn what the codes indicate.
2. Examine the Codes
The meaning of the codes is typically displayed with the fault codes in high-end scan tools. If you have one of those inexpensive scan kits, you might just obtain alphanumeric codes, which you must look up in the OBDII handbook, or enter into a Google search to determine the source of the misfire. Several misfire codes include;
- Every cylinder Random or erroneous firing: Code P0300
- Cylinder 1 misfire: Code P0301
- Cylinder 2 misfires: Code P0302
- Cylinder 3 misfire: Code P0303
- Cylinder 4 misfire: Code P0304
- Cylinder 5 misfires: Code P0305
- Cylinder 6 misfired. Depending on the number of cylinders, the codes continue in that order: Code P0306
AMG Mercedes 12-cylinder engine by LarryStevens / CC BY-SA 3.0. Depending on many factors, repairing a misfiring engine may be expensive. It depends on the year, make, and model of your car in addition to the reason the misfire occurred.
You can usually identify misfiring cylinders using fault codes. You must rule out any potential causes if you receive a random misfire code. Let’s take a closer look at each potential reason now.
3. Test the Ignition
You should be aware that most misfires are typically caused by ignition issues. It’s a great place to start if your diagnostic tool did not identify ignition as the cause of the misfire. If you have an older vehicle with a distributor, you should check it first.
Remove the distributor cover to inspect the interior for any worn-out or corroded connections and points. If the connectors are the problem, you might want to spend a few dollars replacing the distributor cover. The distributor itself must be replaced, which will cost more, but the repair is simple and cheap.
If your car has an ignition coil, you can quickly identify the offending cylinder (s). When you start your car, pay attention to the sound of the engine. Detach one of the ignition coils and turn off the vehicle after that. Launch the vehicle. The sound of the engine should alter.
If not, you’ve discovered the misfiring cylinder. You must carry out this procedure one at a time until all of the misfiring cylinders are located. This procedure can also be done when the engine is idling, but we don’t advise it because you risk electrocuting yourself.
If a cylinder starts to misfire, switch the ignition coil or cable and run the test again. If the misfiring persists after switching cylinders, your ignition coil or wire may be defective. Replace it and get a new one. However, you must inspect your spark plugs if the misfire only affects one cylinder.
Similar to how you test the ignition coils, you may easily check your spark plugs. Replace the spark plugs in the two cylinders to determine if the misfire is limited to that cylinder or if it is caused by the spark plug itself. If the misfire continues, your spark plug is defective. Purchase fresh plugs and replace them all. The misfire issues have been resolved.
Check your intake manifold for leaks if all the cylinders are producing good sparks but the engine is still misfiring.
4. Look for Leaks In the Intake Manifold
It’s rather simple to identify vacuum leaks around your intake manifold. However, because there is a chance of harm, you must take the appropriate safety measures.
Before beginning this operation, make sure you have a fire extinguisher close at hand in case there is a fire. Start your automobile, and let it run for a minute or two.
Spray some starting fluid around any potential trouble spots. Make sure to spray the gasket on the intake manifold. You can get in touch with your mechanic if you lack the confidence to accomplish this.
When you spray on a certain region, if your engine revs, there probably is a vacuum leak there. You must stop the leak. You must proceed to the compression test if you determine that the vacuum leak is not the root of the problem.
5. Test of Compression
To perform a compression test, you will require a special tool. I suggest purchasing the Innova 3612 compression tool. You can also use a compression tool for this test if you already have one. There are more durable and pricey instruments available. You don’t need to spend a lot of money to use the Innova 3612 if you don’t make many engine repairs.
Ignition problems are frequently the root of misfires. If the diagnostic tool does not pinpoint ignition as the root of the misfire, here is a wonderful place to start. You should check the distributor first when you own an older car.
The Innova 3612 is reasonably priced and compatible with practically all makes and models of vehicles.
It has a variety of fittings that allow it to attach to any spark plug tube. The first step in doing this test is to remove the spark plugs from the cylinders that aren’t firing properly. The spark plug tubes should be connected to the compression tester hose.
Make that the opposite end of the line is attached to the compression tester. The next step is to unhook your ignition coil so that it won’t start firing while the test is being done.
While you read the gauge, have a helper turn the ignition for about 10 seconds. Note the readings in writing. Fill the spark plug tubes with a drop of engine oil. The oil container’s cap can be poured in half. Return the ignition key while reconnecting the compression tester kit. Also note this reading down.
The second test should have a greater score than the first. Now you have to repeat this procedure with the other good-functioning cylinders. It’s a good sign that you have low compression if you notice that one or more of your cylinders are lower than the rest.
Workout cylinder walls or faulty piston rings may be to blame for the misfire if low compression is the cause.
Unfortunately, there is no quick or inexpensive cure for this. If you want to keep the car, the engine needs to be rebuilt or replaced. There is one more item you need to check to identify the root of your engine misfire if all the tests performed thus far, including the compression test, come up positive.
6. Examine the Gasoline Delivery
Please take note that if you experience a misfire on every cylinder, it’s probably due to low fuel pressure difficulties. Make sure the fuel regulator is properly set if that is the situation. Make sure your filter is not clogged.
In addition, make sure you replace any broken parts and check that your fuel pump is exporting fuel at the required PSI.
But if you take all the above-mentioned precautions and still only have one or two good cylinders, you most likely have a bad fuel injector. First, make sure that the aforementioned injector is receiving voltage. A voltmeter can be used to accomplish this. You must make a professional support contact if the ignition isn’t working.
If the injector receives power, you must test it using the same method you used to test the spark plugs and ignition coils. Check to see whether the misfire will move to the new cylinder by switching the ignition coil. If it does, your fuel injector is faulty. Please swap it out with a new one.
Guidelines on Preventing Engine Misfires
- Attending the periodic maintenance recommended in your owner’s manual is one of the most reliable strategies to prevent cylinder misfires.
- Make sure your engine is tuned according to factory requirements. A yearly examination will assist in identifying any infant issues that might have caused a misfire.
- After refueling, always be sure you torque down your gas cover. This will lessen the chance of EVAP system issues.
- To assist prevent system line corrosion, use enough rust prevention.
- Any caution light that is on should always be taken seriously. If you ignore it, a minor problem could become a significant one.
- When it comes to keeping your car healthy and safe, don’t be penny-wise and pound-foolish.
- As advised in your owner’s manual, schedule system maintenance, and maintenance tune-ups to keep your engine in top shape. It is a surefire method of preventing early system failures.
- Every 30,000 miles, make sure you perform expert fuel system maintenance. This will ward off carbon buildups, the EGR system’s worst enemy.
Can a Misfire Destroy an Engine?
If an engine is misfiring while you’re driving, it could lead to serious issues. It can result in issues that may necessitate rebuilding or replacing your complete engine, in addition to rough acceleration, slow acceleration, harsh acceleration, changes in sound, and vibrations.
How Much Can Repair for an Engine Misfire Cost?
A misfiring engine can be expensive to repair depending on many variables. It depends on the make and model of your car as well as what caused the misfire.
However, you need to budget $70-$100 for diagnostics to identify the problem’s true cause and extract the error codes. Spark plug replacement is the most frequent repair and costs $200 to $300 for a 4-cylinder engine. V6 and V8 engines should cost between $400 and $500.
How Long Is a Misfiring Engine Advisable?
The severity and origin of the misfire must be considered. However, a misfiring engine can typically keep most cars running for 40,000 to 50,000 miles. I’m sure you wouldn’t want to put yourself through this much stress over a misfiring engine. To prevent severe engine damage, I advise you to identify and treat cylinder misfires as soon as you observe any symptoms.
Can a Misfire Be Corrected By an Engine Cleaner?
No, and yes. The solitary factor is what led to the misfire. It won’t help if the ignition coil or spark plugs are the problem and are to blame for the misfire. However, if the gasoline filter is to blame, the cleaner may be able to stop the cylinder misfire.
You have seen some potential causes for engine misfiring; typically, cylinder problems are to blame. However, you have also seen some simple procedures for identifying and resolving misfire problems.
As you switch the ignition coils, wires, and spark plugs, it’s important to pay attention and listen carefully. Your best option is to seek professional assistance if you lack the confidence necessary to identify and resolve engine misfiring problems on your own.
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.”