An engine misfire feels like a sudden stumble or shudder, almost as if the engine momentarily lost power. You might feel it at idle, during acceleration, or both. Left unchecked, persistent misfires can destroy your catalytic converter and cause raw fuel to wash oil from the cylinder walls, leading to accelerated engine wear.
Most misfires trace back to one of three systems, and an OBD2 scanner can point you directly at the problem cylinder.
What a Misfire Feels Like
At idle, the engine may shake or vibrate more than usual. During acceleration, you’ll feel a hesitation, jerking, or loss of power. In severe cases, the check engine light flashes, indicating an active misfire that needs immediate attention.
Other symptoms include rough idle, reduced fuel economy, and a raw fuel smell from the exhaust. Any combination of these signs warrants a scan for trouble codes.
Reading the Misfire Code
OBD2 codes P0300 through P0312 identify misfires. P0300 means random misfires across multiple cylinders. Codes P0301 through P0312 indicate a specific cylinder (P0301 = cylinder 1, P0304 = cylinder 4, and so on).
A cylinder-specific code is actually helpful because it narrows the problem to three possible components on that cylinder: the spark plug, the ignition coil, and the fuel injector.
OBD2 Scanner
Essential for reading misfire codes and identifying which cylinder is affected
Most Common Misfire Causes
Worn Spark Plugs
Spark plugs wear down over time as the electrode erodes. Most 2026 engines use iridium or double-platinum plugs rated for 60,000 to 100,000 miles, but they can fail earlier if the engine runs hot or the fuel mixture is off.
Pull the plug from the misfiring cylinder and inspect it. A worn electrode, cracked insulator, or heavy carbon buildup all indicate the plug needs replacing. A fresh set of iridium spark plugs is the cheapest and most common misfire fix.
If you’ve experienced hesitation during acceleration, worn spark plugs are often the culprit behind that symptom as well.
Iridium Spark Plugs
The most common and affordable misfire fix, rated for 60,000-100,000 miles
Failed Ignition Coil
Each cylinder on a modern engine has its own ignition coil (coil-on-plug design). When a coil fails, it can’t deliver enough voltage to fire the spark plug reliably. The misfire usually worsens under load.
Here’s a useful diagnostic trick: swap the ignition coil from the misfiring cylinder with one from a cylinder that’s running fine. Clear the codes and drive. If the misfire follows the coil to the new cylinder, you’ve confirmed the coil is bad. If the misfire stays on the original cylinder, the problem is the plug or injector.
Fuel Injector Problems
A clogged or leaking fuel injector delivers too little or too much fuel, causing a misfire. You can sometimes hear a clicking sound from each injector using a mechanic’s stethoscope or a long screwdriver held against each injector (place the handle end to your ear).
Fuel injector cleaning additives can clear minor clogs. Severely clogged or electrically failed injectors need replacement.
Less Common Causes
Vacuum leaks, low fuel pressure, a clogged catalytic converter, and low compression from worn piston rings or valves can all cause misfires. These are less likely on newer vehicles but worth investigating if plugs, coils, and injectors check out fine.
A compression test with a compression tester reveals internal engine issues. All cylinders should read within 10% of each other. A cylinder that’s significantly lower than the others may have a burned valve or worn rings.
If you’re shopping for a vehicle, be aware that some models are more prone to engine problems than others. Check our guide on the worst used cars to buy with high mileage to avoid vehicles with known misfire and engine issues.
When searching for reliable vehicles that won’t leave you stranded with misfires, our list of best used cars under competitively priced that will last 200,000 miles highlights models known for engine durability.
Frequently Asked Questions
Can I drive with an engine misfire?
A steady check engine light with occasional misfires is drivable short-term. A flashing check engine light indicates an active misfire that can damage the catalytic converter. Reduce speed and get it diagnosed as soon as possible.
How much does it cost to fix a misfire?
Spark plug replacement is the least expensive fix. Ignition coil replacement is moderate. Fuel injector replacement or internal engine repairs are more costly. Starting with the cheapest, most likely cause saves money.
Can bad gas cause a misfire?
Yes. Contaminated fuel or fuel with too much ethanol can cause misfires. If the misfire started immediately after filling up, try adding a fuel system cleaner and running the tank low before refilling with fuel from a different station.
Will a misfire always trigger a check engine light?
Not always immediately. Minor, intermittent misfires might not set a code right away. Once the engine computer detects a pattern of misfires, it will illuminate the check engine light. A flashing light means the misfire is severe and happening right now.
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