Engine Misfire Symptoms & How to Fix It
Chances are, you’re dealing with an engine misfire—a common issue that can lead to rough idling, poor acceleration, and even serious engine damage if ignored.
But don’t worry! I’ll break down everything you need to know about engine misfires—what causes them, how to identify the problem, and the steps to fix it.
Even if you’re not a mechanic, We will help you understand the issue in simple terms so you can fix it yourself or communicate better with your mechanic. Let’s get started!
What is an Engine Misfire?
A misfire happens when one or more engine cylinders don’t burn the air-fuel mixture correctly. Your engine runs on controlled explosions inside the cylinders, and when one of these explosions doesn’t happen correctly, the engine stumbles, loses power, or shakes.
Think of it like a heart skipping a beat—your engine won’t run smoothly, and it can cause poor fuel efficiency, increased emissions, and even long-term engine damage.
Now, let’s look at the signs that show your car might be misfiring.
Symptoms of an Engine Misfire
Misfires don’t always mean your engine will stop running completely. Sometimes, the symptoms are subtle at first but get worse over time. Here’s what to watch for:
1. Rough Idling & Vibrations
When your car is at a stoplight or in park, does the engine shake or feel rough? A smooth-running engine should idle without noticeable vibrations. If it feels unsteady, a misfire could be happening.
2. Loss of Power & Poor Acceleration
Does your car feel slow, have trouble speeding up, or hesitate when you step on the gas? Misfires prevent cylinders from producing full power, making your car slow and unresponsive.
3. Check Engine Light (CEL) is On
A misfire triggers the check engine light, and if it’s flashing, it means the issue is severe. You should stop driving immediately and diagnose the problem.
Quick Tip: Use an OBD2 scanner to check for trouble codes like P0301 (cylinder 1 misfire) or P0303 (cylinder 3 misfire). This tells you exactly which cylinder is affected.
4. Unusual Noises (Popping, Sputtering, or Backfiring)
When a misfire happens, you might hear:
✔ Popping or sputtering from the engine
✔ A loud bang (backfire) from the exhaust
✔ A coughing or chugging noise when accelerating
These sounds happen when fuel doesn’t burn properly in the cylinder and ignites somewhere else instead.
5. Poor Fuel Economy
A misfiring engine wastes fuel because the combustion process isn’t efficient. If you notice your gas mileage dropping, it could be due to unburnt fuel being wasted.
6. Strong Fuel Smell from the Exhaust
If fuel isn’t being burned properly in the engine, it may exit through the exhaust, creating a strong gasoline smell.
7. Engine Stalling or Hard Starting
A severe misfire can make your engine stall while driving or struggle to start. If multiple cylinders misfire, the engine may even refuse to start altogether.
What Causes an Engine Misfire?
Misfires don’t just happen randomly—there are three main reasons why they occur:
1️⃣ Ignition System Problems
Your engine needs a strong spark to burn the fuel properly. If any part of the ignition system fails, a misfire can occur.
🔹 Worn-out spark plugs – Over time, spark plugs can wear down or get covered in carbon buildup, making them less effective.
🔹 Faulty ignition coils – A weak coil can’t provide enough voltage for a strong spark.
🔹 Bad spark plug wires – Damaged wires prevent electricity from reaching the spark plug.
2️⃣ Fuel System Issues
Your engine also needs the right amount of fuel to burn correctly. If there’s too much or too little, misfires happen.
🔹 Clogged fuel injectors – Dirt or carbon buildup prevents proper fuel flow.
🔹 Weak fuel pump – Low fuel pressure can lead to a weak fuel supply, causing the engine to misfire.
🔹 Dirty fuel filter – A clogged fuel filter can block fuel flow, making it harder for the engine to run smoothly.
3️⃣ Air & Compression Issues
Engines also need the right air-fuel ratio and compression to function properly. If these are off, misfires can occur.
🔹 Vacuum leaks – Extra air entering the engine disrupts the air-fuel mixture.
🔹 Faulty MAF sensor – A bad Mass Air Flow (MAF) sensor can send incorrect airflow data to the ECU.
🔹 Low cylinder compression – Bad piston rings, leaky valves, or a blown head gasket can lower engine compression.
Now that we know the reasons, let’s fix the misfire!
How to Fix an Engine Misfire (Step-by-Step)
Step 1: Use an OBD2 Scanner to Find the Problem
✔ Plug in an OBD2 scanner (found at auto parts stores).
✔ Check for codes like P0301 to P0306. These show misfires in certain cylinders.
✔ Identify which cylinder is misfiring before replacing parts.
Pro Tip: Some auto parts stores will scan your car for free!
Step 2: Inspect and Replace Spark Plugs
✔ Take out the spark plug from the cylinder that is misfiring.
✔ Check for carbon deposits, cracks, or oil buildup.
✔ Replace it if necessary and ensure the gap is correct.
Did you know? Platinum and iridium spark plugs last longer than copper ones.
Step 3: Test the Ignition Coils & Spark Plug Wires
✔ Move the ignition coil to another cylinder and check if the misfire moves too.
✔ If it does, replace the bad coil.
✔ Check spark plug wires for damage and replace them if needed.
Step 4: Clean or change the fuel injectors.
✔ Pour fuel injector cleaner into your gas tank.
✔ If the misfire persists, remove and clean the fuel injector manually.
✔ Replace the injector if it’s clogged beyond repair.
Step 5: Check for Vacuum Leaks
✔ Spray carburetor cleaner around the intake manifold and vacuum hoses.
✔ If the engine RPM changes, there’s a vacuum leak that needs fixing.
Step 6: Check the Fuel Pressure and Fuel Pump.
✔ Attach a fuel pressure gauge to the fuel rail.
✔ Compare the pressure reading to manufacturer specs.
✔ If it’s too low, the fuel pump or filter may need replacement.
Step 7: Perform a Compression Test (If Needed)
✔ Remove spark plugs and insert a compression tester.
✔ Crank the engine and check if the compression is within spec.
✔ Low compression means worn rings or valves may need repairs.
How to Prevent Engine Misfires
✅ Replace spark plugs every 30,000 – 100,000 miles (check your car’s manual).
✅ Use high-quality fuel and clean injectors regularly.
✅ Fix vacuum leaks and replace air filters when needed.
✅ Look at the ignition coils and spark plug wires for damage.
A misfire should never be ignored because it affects fuel economy, power, and long-term engine health. The best part? You can find and fix most misfires using the steps above!
Relevant Article: Bad Spark Plug Symptoms: Identify, Fix & Prevent Issues
