A misfiring cylinder will damage your engine if you keep driving
You should not drive with a misfiring cylinder for more than a few miles. A misfire means one of your engine's cylinders is not firing properly — the spark plug is not igniting the fuel, the fuel injector is clogged, the compression is low, or the ignition coil has failed. Every time that cylinder fails to fire, unburned fuel enters your exhaust system and catalytic converter, where it ignites and causes heat damage. The longer you drive, the more likely you are to crack or destroy the catalytic converter, which costs $800 to $2,500 to replace.
Beyond the catalytic converter, a misfiring cylinder also overheats your engine block, wears out your spark plugs faster, and can eventually cause internal engine damage that makes the engine unrepairable. The exact timeline depends on how severe the misfire is — a cylinder that misfires once every few seconds is more dangerous than one that misfires occasionally — but you should treat any misfire as a reason to stop driving and have the engine diagnosed.
Key Takeaways
- A misfiring cylinder sends unburned fuel into your catalytic converter, which overheats and cracks within a few hundred miles of continuous driving.
- The longer you drive with a misfire, the greater the risk of permanent engine damage that cannot be repaired, only replaced.
- A single misfire code (P0300 through P0308) means one cylinder is not firing; multiple codes mean multiple cylinders are failing.
- Stopping and having the engine scanned at a repair shop is the only way to know whether the misfire is from a spark plug, fuel injector, ignition coil, or compression loss.
What happens to your engine when a cylinder misfires
When a cylinder misfires, the fuel that should have burned inside that cylinder instead flows into the exhaust manifold unburned. Your catalytic converter is designed to burn leftover fuel, but it is not designed to burn the amount of fuel that comes from a misfiring cylinder. The converter overheats, and the internal ceramic honeycomb structure begins to crack and break apart. Once the honeycomb is damaged, it cannot be repaired — the entire converter must be replaced.
At the same time, the unburned fuel that reaches your engine oil dilutes it and reduces its ability to lubricate moving parts. Your engine runs hotter because one cylinder is not producing power, forcing the other cylinders to work harder. Spark plugs wear out faster. If the misfire is caused by low compression in that cylinder, metal-to-metal contact inside the cylinder increases friction and heat, accelerating wear on the piston rings and cylinder walls.
The damage is not always visible or felt while you are driving. You may notice rough idle, a loss of power when accelerating, or a check engine light. You may feel nothing at all. But the damage is happening with every mile you drive.
How far you can drive before catalytic converter damage becomes permanent
Most catalytic converters begin to fail after 100 to 300 miles of continuous driving with a severe misfire. A severe misfire is one where the cylinder misfires multiple times per second — you will feel the engine shaking and hear a loud popping sound from the exhaust. A mild misfire, where the cylinder misfires occasionally, may take longer to damage the converter, but the damage is still happening.
The exact distance depends on how hard you are driving. Highway driving at constant speed produces less heat than city driving with frequent acceleration and braking. Towing or driving uphill puts more load on the engine and makes the misfire worse. Cold weather can also mask a misfire because the engine runs richer (more fuel) to warm up, which can hide the problem until the engine warms up and the misfire becomes obvious.
The safest approach is to treat any misfire as an emergency: stop driving, turn off the engine, and have it scanned for diagnostic trouble codes. Do not drive to the repair shop if the misfire is severe. Call a tow truck instead.
Diagnostic codes that tell you which cylinder is misfiring
When your check engine light comes on, a scan tool reads a diagnostic trouble code that tells you which cylinder is misfiring. The codes are P0300 (random misfire), P0301 (cylinder 1), P0302 (cylinder 2), P0303 (cylinder 3), and so on through P0308 (cylinder 8, on engines with eight cylinders). A code like P0301 means cylinder 1 is misfiring consistently. A code like P0300 means the engine is misfiring randomly across multiple cylinders, which usually signals a fuel system problem or ignition system problem that affects all cylinders.
If you see multiple misfire codes at the same time — for example, P0301 and P0302 — it usually means a problem that affects more than one cylinder, such as a fuel filter clog, low fuel pressure, or a bad ignition coil that controls multiple cylinders. A single code means the problem is isolated to that one cylinder.
You can read these codes yourself with an inexpensive code reader (around $25 to $50), or a repair shop can read them for you. The code tells you which cylinder to focus on, but it does not tell you what is causing the misfire — that requires a mechanic to test the spark plug, fuel injector, ignition coil, and compression in that cylinder.
Common causes of misfires and how quickly each one damages the engine
A bad spark plug is the most common cause of a misfire and usually the least expensive to fix. A spark plug that is fouled (covered in carbon or oil), gapped too wide, or straightforward worn out will not ignite the fuel. Replacing spark plugs costs $50 to $300 depending on how many cylinders your engine has and how difficult they are to access. Driving with a bad spark plug for a few hundred miles will damage the catalytic converter but usually not the engine itself.
A clogged fuel injector causes the cylinder to receive too little fuel, so the mixture is too lean to ignite. This misfire is usually accompanied by a rough idle and loss of power. Cleaning or replacing a fuel injector costs $50 to $900 depending on whether the injector can be cleaned or must be replaced. Driving with a clogged injector for a few hundred miles will damage the catalytic converter.
A bad ignition coil prevents the spark plug from firing at all. Ignition coils are mounted directly on top of the spark plugs on most modern engines. A bad coil costs $100 to $400 to replace. This is one of the most dangerous misfires because the cylinder receives no spark at all, so all the fuel flows into the exhaust unburned. Driving with a bad ignition coil for more than 100 miles risks serious catalytic converter damage.
Low compression in a cylinder means the piston rings or cylinder walls are worn, or a valve is stuck open. This is the most serious cause of a misfire because it signals internal engine damage that has already begun. Compression testing costs $100 to $200. If compression is low, you should not drive the engine at all — continuing to drive will accelerate the wear and may make the engine unrepairable.
What to do if your engine is misfiring right now
First, check your fuel tank. If your fuel is low or you are using fuel with a low octane rating (87 instead of 91, for example), fill up with high-octane fuel and drive for a few miles. Sometimes a misfire is caused by fuel that is too old or contaminated, and fresh fuel can clear it. If the misfire continues, move to the next step.
Second, have the engine scanned for diagnostic codes. You can do this yourself with a code reader, or a repair shop can do it for you. Write down the exact code (P0301, P0302, etc.) and any other codes that appear. If the code is P0300 (random misfire), the problem is likely in the fuel system or ignition system and affects all cylinders.
Third, take the engine to a repair shop for diagnosis. Bring the diagnostic codes with you. A mechanic will test the spark plug, fuel injector, ignition coil, and compression in the misfiring cylinder to find the cause. Do not drive the engine hard or for long distances while waiting for the appointment. If the misfire is severe (you can feel the engine shaking), call a tow truck instead of driving.
When to tow instead of drive
Tow the engine if the misfire is severe enough that you can feel the engine shaking, or if the check engine light is flashing instead of steady. A flashing check engine light means the misfire is so bad that unburned fuel is entering the catalytic converter in large amounts, and the converter is overheating right now. Driving even a short distance with a flashing check engine light can cause permanent catalytic converter damage.
Also tow if you have already driven more than 200 miles with a known misfire. The catalytic converter damage is likely already severe, and driving further will only make it worse. Towing costs $75 to $150 depending on distance, which is much less than a $1,500 catalytic converter replacement.
Frequently Asked Questions
Can I drive to the repair shop if my check engine light is on but not flashing?
Yes, but only if the misfire is mild — you should not feel the engine shaking. Keep the drive short (under 10 miles if possible) and avoid highway speeds and hard acceleration. If the misfire gets worse or the light starts flashing, pull over and call a tow truck.
Will a misfire go away on its own?
No. A misfire is always caused by a specific problem — a bad spark plug, clogged injector, bad ignition coil, or low compression. The problem will not fix itself, and the longer you drive, the more damage it causes. The only way to stop a misfire is to find and fix the cause.
What does a flashing check engine light mean?
A flashing light means the misfire is severe and the catalytic converter is overheating right now. Stop driving when ready and call a tow truck. Continuing to drive risks destroying the converter in the next few miles.
How much does it cost to fix a misfire?
The cost depends on the cause. A bad spark plug costs $50 to $300 to replace. A clogged fuel injector costs $50 to $900. A bad ignition coil costs $100 to $400. If the misfire is caused by low compression, the engine may need internal repairs that cost $1,000 to $5,000 or more. The longer you drive with a misfire, the more likely you are to damage the catalytic converter ($800 to $2,500), which adds to the total cost.
Can I drive with one misfiring cylinder if my engine has eight cylinders?
You can drive short distances, but you should not drive long distances or at highway speeds. One misfiring cylinder means the other seven cylinders are doing all the work, which overheats the engine and accelerates wear. The catalytic converter is also being damaged by unburned fuel. Have the misfire diagnosed and fixed as soon as possible.