When your car’s engine misfires, it can feel like a hiccup or a sudden jolt while driving. This issue happens when one or more cylinders in the engine fail to complete the combustion process properly.
While an occasional misfire might not seem serious, ignoring it can lead to bigger problems, including reduced fuel efficiency, higher emissions, or even engine damage. Let’s break down what causes engine misfires and how you can fix them.
What is Engine Misfiring?
Engine misfiring occurs when one or more of the engine’s cylinders fail to ignite the fuel-air mixture properly.
This issue can lead to a variety of problems, from reduced power and fuel efficiency to more serious engine damage if not addressed promptly.
Misfires can happen intermittently or continuously, and they often trigger the check engine light, signaling the need for diagnostic evaluation and repair.
What causes Engine Misfire?
Understanding misfiring engine causes is a step toward fixing the problem and avoiding them from happening. Let’s have a close look at the causes of a misfiring engine.
#1. Spark Plugs.
Worn or fouled spark plugs are one of the most common causes of engine misfires. These small but crucial components deliver the spark that ignites the fuel in your engine. If they’re not working properly, your engine won’t be firing on all cylinders.
Warning signs of worn spark plugs include poor fuel economy, loss of power, and difficulty starting the engine. To fix this issue, check your spark plugs and replace them if they’re worn or dirty.
#2. Ignition Coils.
Another possible cause of an engine misfire is a bad or malfunctioning ignition coil. Ignition coils convert the low-voltage output of a car’s battery into the high-voltage punch that fires your engine’s spark plugs.
A malfunctioning coil can cause a misfire in the cylinder it serves. Tell-tale signs of a bad coil are a rough idle, poor fuel economy, and a check engine light. Have a qualified mechanic take a look and replace the bad coil as necessary.
#3. Fuel Injectors.
A clogged or malfunctioning fuel injector can cause a misfire if it fails to deliver the proper fuel to one of your engine’s cylinders. Here, warning signs include a rough-running engine at idle, poor mileage, and a “Check Engine” warning light.
A qualified mechanic can easily test your fuel injectors and replace any if they’re clogged or malfunctioning.
#4. Vacuum Leaks.
A vacuum leak in the intake manifold gasket or a vacuum hose can also cause an engine misfire. This kind of leak causes what’s known as a lean misfire, a situation in which there’s too much air and too little fuel in your car’s air-fuel mixture.
Watch for reduced gas mileage, rough idling, and a dashboard warning light if you have a vacuum leak. A qualified mechanic has the tools to diagnose, locate and fix the problem.
#5. Mass Airflow Sensor.
The mass airflow sensor (MAF) measures the air entering the engine. Your car’s Electronic Control Unit, or ECU, uses the info to optimize the engine’s air-fuel mix. A dirty or faulty MAF causes a mix that’s either too rich or too lean, and that causes a misfire.
Engines with a MAF problem will get poor mileage, run rough (or not at all), and trigger the check engine light. Have a qualified mechanic clean or replace the MAF.
Symptoms of Engine misfiring
Before we move into diagnosing your car for a misfire, there are a few symptoms you need to watch out for.
#1. Engine warning light.
If your car develops a misfire as a result of bad Injectors, lousy spark plugs, low fuel pressure, or any other causes, it will cause the warning light to pop in the dashboard. The check light indicates problems in the engine system.
Modern cars have an electronic module, also known as the car computer. If any part of the engine starts malfunctioning, these sensors will send a signal to the computer.
The computer will analyze how severe the problem is, and if the issues require urgent attention, it’ll light up the check engine light to notify the driver of the problem.
You have to bear in mind that many other factors can also trigger the check light. You want to diagnose your car once the light pops up to ascertain the actual cause of the problem.
#2. Rough idle.
A triggered check light might not take your mind to a misfire, but one noticeable sign of misfiring is rough idling.
A rough idle can be a result of several things. It could result from bad spark plugs, vacuum leaks, clogged fuel filters, or a lean running engine. If the rough idling results from a lean running engine, it might cause severe engine damage.
#3. Slow Acceleration.
A misfiring engine will affect your air-fuel mixture ratio. When this happens – it will send false data to other components.
One of these components is the oxygen sensor. If the oxygen sensors send false data because of the inappropriate air-fuel ratio, it will cause the car computer to slow acceleration.
This symptom will be more noticeable in cars with turbochargers. The engine won’t receive the demanded air or boost, causing a bad driving experience.
#4. Rough acceleration.
A misfiring engine can also cause your car to experience rough acceleration. As the engine gets to higher rpm while accelerating, you may experience jerking and surging while driving. Engine misfire when accelerating is the surest way to tell you to have a misfire.
#5. Change in Engine Sound.
If you’re not an automobile engineer with field experience, you might find it hard to spot this symptom. The truth is, that engines make different sounds. A v8 engine sounds different from a V6 or 4cylider engine.
One or more cylinders may stop working entirely during misfiring, and your 4cylinder engine becomes a 3 or 2cylinder. In most cases, only a trained ear will notice an engine misfire sound.
A loss of a single or more cylinders will produce a different engine sound, indicating a severe misfire. This will also result to slow acceleration. In a V8 engine, a loss of two cylinders will lose 25% of engine capacity.
However, in a 4cylinder, a loss of two cylinders will lose 50% of the engine capacity. If you have a dead cylinder during misfire, you can easily track it down on a 4cylinder than the V8 engine.
#6. Engine Vibrations.
Car manufacturers undergo expensive procedures to ensure you have a balanced engine. When you have a misfire, that balance is lost. You’ll notice that your car vibrates while idling or accelerating.
If the car is parked on even ground, you may open your hood and see how it’s vibrating. The vibration increases depending on how many misfiring cylinders are in the engine.
Diagnosing Engine Misfires
Diagnosing the cause of an engine misfire involves a systematic approach. Here’s a step-by-step guide to help you pinpoint the issue:
Step 1: Check for Trouble Codes.
Modern vehicles are equipped with onboard diagnostics (OBD-II) systems that store trouble codes when a malfunction occurs.
Use an OBD-II scanner to retrieve these codes. Common misfire-related codes include P0300 (random/multiple cylinder misfire) and P0301-P0308 (specific cylinder misfire).
Step 2: Inspect Spark Plugs.
Spark plugs are a common culprit for engine misfires. Remove and inspect each spark plug for signs of wear, fouling, or damage. Replace any faulty spark plugs and ensure they are properly gapped.
Step 3: Examine Ignition Coils.
Ignition coils convert the battery’s voltage into a high-voltage spark needed for combustion. Test the ignition coils using a multimeter or swap them between cylinders to see if the misfire follows. Replace any defective ignition coils.
Step 4: Check Fuel Injectors.
Fuel injectors deliver fuel to the engine’s cylinders. A clogged or malfunctioning injector can cause a misfire. Listen for a clicking sound from each injector using a mechanic’s stethoscope. If an injector is silent or inconsistent, consider cleaning or replacing it.
Step 5: Inspect Vacuum Leaks.
Vacuum leaks can disrupt the air-fuel mixture, leading to misfires. Use a smoke machine or a can of carburetor cleaner to check for leaks around hoses, gaskets, and the intake manifold. Repair any leaks found.
Step 6: Test Compression.
Low compression in one or more cylinders can cause misfires. Perform a compression test using a compression gauge.
Compare the readings to the manufacturer’s specifications. If compression is low, investigate further for possible causes such as worn piston rings or a blown head gasket.
Step 7: Check the EGR Valve.
The Exhaust Gas Recirculation (EGR) valve recirculates exhaust gases to reduce emissions. A faulty EGR valve can cause rough idling and misfires. Test the valve and replace it if necessary.
How to Fix an Engine Misfire?
Fixing an engine misfire starts with checking all the codes. A code reader will be able to help you determine if there’s a coil, spark plug, or sensor problem.
You can also use a compressor test kit to check for compression issues. An OBD II code reader will be able to tell you which cylinders the misfire occurred on.
#1. Fixing a Misfired Caused by a Bad Ignition Coil or Spark Plug.
A misfire caused by an ignition coil or coil pack going out usually ends up also causing a spark plug problem. Though it’s hard to tell if the cause of the engine misfire is the coil or the spark plug, they both act very similarly.
You can confirm which one the culprit is by separating the ignition coil from the suspect spark plug. Then move the suspect spark plug and ignition coil to different cylinders.
At that point, you clear the codes and take the car for a test drive knowing full well that it’s going to misfire at some point.
You head back nice and slow when it does and hook the code reader up again. If it throws a code for a different cylinder, you’ll be able to determine if it was the spark plug or the ignition coil.
Usually, when you need to replace a bad ignition coil, it only makes sense to spend a few extra minutes replacing a potentially foiled spark plug with a fresh new one. This gives you some added peace of mind while only adding an extra $25 or so to the repair cost.
#2. Fixing an Engine Misfire Caused by an Air Leak.
Fixing an engine misfire caused by an air leak is supposed to be easy, but I’ve had times when I felt like I was chasing gremlins. The bush fix diagnostic that seems to work best here is to start the engine and let it run until it’s idling normally.
Then spray a little bit of carb cleaner or starting fluid around the engine where you suspect a leak. If there’s an air leak, it will suck some of this mildly flammable aerosol fluid in, which will cause the engine to cycle a little faster.
This is one of those things that can be frustrating if you do it too fast. So go slow and steady, use a small amount and be wise enough to keep a fire extinguisher nearby.
Once you find the air leak, you’ll have to complete the correct repair to get the fuel/air mixture back to a controlled ratio.
#3. Repairing an Engine Compression Problem.
Repairing a misfire caused by a compression problem can be an expensive fix. A compression tester will give you a good idea of where the compression problem is. Once you’ve narrowed it down, you’ll have to inspect the suspect engine components.
This includes the valves, piston rings, and timing belts. Any one of which can be a seriously costly repair.
This might be beyond what a home mechanic can do, but at least you’ll be better informed about the problem if you need to take it to a professional mechanic to handle the repair.
#4. Fixing an Engine Misfire Caused by a Fuel System Problem.
The first step in fixing a misfire caused by a fuel system problem is to replace the fuel filter. It needs to be done anyway if it’s already been over 30,000 miles since you last had it replaced.
This will also help you diagnose other fuel system parts should the misfire persist. Once you’ve replaced the old fuel filter, you can test the fuel system pressure with an electronic or manual tester.
Hooking the manual tester up to the fuel rail will give you the most reliable result. You can then compare the reading to the manufacturer’s specs.
If it’s too low and you’ve already replaced the fuel filter, you likely need to replace the fuel pump. If the fuel pressure reading is too high, then you might need to replace the fuel regulator.
#5. Fixing an Engine Misfire Caused by Bad Sensors.
Fixing an engine misfire caused by a bad sensor is usually as straightforward as installing a new replacement. Then you just need to clear the codes with the code reader.
Just be prepared for one sensor to be bad, you replace it, and a few weeks later, another one goes. They often seem to have a similar lifespan.
Effects of Engine Misfires
Engine misfires can have a significant impact on the performance and safety of a vehicle. Understanding the effects of these misfires is crucial in addressing the issue promptly and preventing further complications.
Fuel Economy
One of the primary effects of engine misfires is a decrease in fuel economy. When a cylinder misfires, it fails to combust the air-fuel mixture efficiently, resulting in wasted fuel.
This inefficiency can lead to reduced mileage and increased fuel consumption over time, affecting both your wallet and the environment.
Safety on the Road
Misfires can compromise safety while driving. When a cylinder misfires, it causes a lack of power, resulting in sluggish acceleration and reduced ability to overtake or react quickly to hazardous situations.
This can put you and other drivers on the road at risk, particularly in critical moments that require immediate responsiveness.
Engine Damage
If left unaddressed, misfiring cylinders can cause severe damage to the engine. When a cylinder misfires, unburned fuel can enter the exhaust system, leading to overheating and potentially damaging crucial engine components.
Ignoring engine misfires can result in costly repairs and even the need for a complete engine replacement.
To prevent these negative effects, it is essential to address engine misfires promptly. Proper diagnosis and repairs by a qualified mechanic can help restore the performance, fuel efficiency, and safety of your vehicle.
What Does an Engine Misfire Sound Like?
Engine misfires can produce distinct sounds that can help identify the issue at hand. These sounds include popping, sneezing, banging, chuffing, and other unusual noises. These noises are often heard when the engine is running between 1,500 and 2,500 RPM.
The sounds are a result of unburnt fuel exiting a misfiring cylinder and being pushed out through the exhaust system.
This can create a series of audible bursts or sharp popping sounds. In some cases, the misfire can even cause the engine to backfire, resulting in a louder and more explosive noise.
When an engine misfires, there may also be changes in the overall engine sound. The engine may struggle or sound rough, indicating a potential misfire issue.
It is important to pay attention to these sounds as they can be a clear indicator of a misfiring cylinder.
| Sound | Description |
|---|---|
| Popping | A series of small bursts or popping sounds |
| Sneezing | A sudden, sharp noise similar to a sneeze |
| Banging | A loud and forceful noise, often accompanied by vibrations |
| Chuffing | A rhythmic noise resembling a puffing or chuffing sound |
Experiencing any of these sounds or changes in engine noise should prompt further investigation to identify and address the misfire issue.
Prevention of Engine Misfires
To ensure your engine runs smoothly and efficiently, it’s important to take proactive measures to prevent and repair engine misfires.
By following regular maintenance practices and addressing any identified issues promptly, you can minimize the risk of misfires and keep your vehicle running at its best.
#1. Regular Maintenance.
One of the key ways to prevent engine misfires is through regular maintenance, which involves replacing spark plugs and maintaining a clean fuel system. Over time, spark plugs wear out and can result in misfires.
By replacing them according to the manufacturer’s recommended schedule, you’ll ensure proper ignition and reduce the chances of misfires.
Additionally, keeping your fuel system clean is crucial. Clogged fuel injectors can disrupt fuel flow and lead to misfires. Using a fuel system cleaner periodically can help remove deposits and maintain optimal performance.
#2. Prompt Repair.
If you encounter any signs or symptoms of an engine misfire, such as rough idling or loss of power, it’s important to address the issue promptly.
Ignoring misfires can lead to further complications and potentially cause more damage to your engine.
Identifying and repairing any underlying issues is crucial for preventing future misfires. Common causes, such as faulty ignition coils or clogged fuel injectors, should be addressed by a certified mechanic.
They have the expertise and diagnostic equipment to accurately identify and repair the problem, ensuring your engine runs smoothly.
#3. Proper Installation and High-Quality Components.
During spark plug replacement, it’s essential to ensure proper installation. Incorrectly installed spark plugs can cause misfires and hinder engine performance. Following the manufacturer’s guidelines for installation can help prevent such issues.
Using high-quality components is also important for preventing engine misfires. Inferior quality spark plugs or ignition coils may malfunction, leading to misfires.
Opting for reputable brands and reliable parts can help minimize the risk of such problems and improve overall engine performance.
“Preventing engine misfires involves regular maintenance, prompt repair of identified issues, and the use of high-quality components.”
By incorporating these preventive measures and promptly addressing any identified issues, you can significantly reduce the likelihood of engine misfires.
Not only will this help maintain the performance and efficiency of your vehicle, but it will also prevent more extensive and costly repairs down the road.
How much can it cause to fix an engine misfire?
The cost of fixing a misfiring engine depends on various factors. It is affected by your car make and model, and the cause of the misfire.
However, you should expect to pay $70-$100 for diagnostics to pull out the fault codes and the actual cause of the problem.
The most common repair is replacing spark plugs which could cause around $200-$300 for a 4cylinder engine. V6 and V8 engines will be around $400-$500.
FAQs.
Q: Can a Misfire go away on its own?
If a car’s misfire is caused by little water in the gas tank or contaminated gas, it will go away on its own. If not, it is likely to return.
Q: Can a misfire ruin an engine?
Driving with a misfiring engine can cause severe problems if left unchecked. Not only will it cause rough idle, slow acceleration, rough acceleration, changes in sound, and vibrations, it can wind up expanding issues that may require rebuilding or replacing your entire engine.
Q: How long can you drive with a misfiring engine?
It depends on the level and cause of the misfire. However, most vehicles can run for 40,000-50,000 miles with a misfiring engine.
I know you wouldn’t want to stress yourself this long with a misfiring engine. I recommend you diagnose and fix cylinder misfires once you notice any symptoms of a misfire to avoid causing catastrophic engine damage.
Q: Will the engine cleaner fix a misfire?
Yes and No. It solely depends on the cause of the misfire. If the cause of the misfire is a defective ignition coil or lousy spark plugs, then it is not going to do anything. But if the cause is a result of a clogged fuel filter, the cleaner may fix the cylinder misfire.
Final word
You have seen several factors that could lead to engine misfire – most at times, it is caused by cylinder issues. Nonetheless, you have also seen several easy-to-do steps to diagnose and fix misfire issues.
The key is to pay attention and listen closely as you swap the ignition coils, wires, and spark plugs. If you are not confident enough to diagnose and fix engine misfiring issues yourself, your best bet is to seek professional assistance.