Engine Misfires Only on One Cylinder - Top Causes, Fixes & What to Do

Certified Professional Automotive Mechanic – Owner and Editor of VehicleRuns

Last Updated: September 29, 2026

Safety note: Troubleshooting guidance can help you narrow down likely causes, but it cannot replace an in-person inspection. If the vehicle feels unsafe, warning lights are flashing, you smell fuel, see smoke, notice overheating, or have problems with braking, steering, or control, stop driving when it is safe to do so and have the vehicle inspected.

If the engine is misfiring on only one cylinder, the problem is usually localized instead of affecting the whole engine. That is useful, because it often narrows the fault to one spark plug, one ignition coil, one fuel injector, one section of wiring, or a mechanical problem in that cylinder.

A single-cylinder misfire can feel like a rough idle, a stumble under load, a flashing check engine light, or a steady shake that gets worse when you accelerate. The key is noticing when it happens, whether it is always the same cylinder, and whether the symptom changes with heat, moisture, or throttle.

Some one-cylinder misfires are relatively simple. Others point to low compression, valve trouble, or a head gasket issue. This guide helps you sort out the most likely causes, what to check first, and when the problem is serious enough to stop driving.

Start by figuring out whether the misfire behaves like a spark problem, a fuel problem, an air leak near one cylinder, or a mechanical issue. The most useful clues are when the misfire is worst, whether it follows a swapped part, and whether that cylinder shows different plug or compression results.

What you notice	Most likely cause	What to check first	Urgency
Rough idle, then better as revs rise	fouled spark plug	Remove and compare that cylinder's spark plug	Diagnose soon
Miss gets worse under load or acceleration	weak ignition coil	Swap the coil to another cylinder and rescan	Can worsen
Misfire stays on same cylinder after swapping parts	injector or compression problem	Check injector pulse, then run compression test	Can worsen
Misfire starts after rain or engine wash	moisture in ignition boot	Inspect coil boot and plug well for water	Diagnose soon
Flashing check engine light and strong shaking	active damaging misfire	Stop driving and scan for cylinder-specific codes	Stop driving

Best first move: Confirm which cylinder is misfiring, then do the simplest isolation test first by swapping the plug or coil with another cylinder.

Safety note: If the check engine light is flashing, the engine is shaking hard, or raw fuel smell is strong, stop driving to reduce the risk of catalytic converter damage.

Table of Contents

Most Common Causes of a One-Cylinder Misfire

On most vehicles, a one-cylinder misfire comes from an ignition fault, a fuel delivery problem at that cylinder, or a cylinder-specific air or mechanical issue. The three causes below are the most common starting points, and a fuller list appears later in the article.

Worn Spark Plug: A worn, fouled, cracked, or fuel-soaked spark plug can stop one cylinder from firing cleanly, especially at idle or under load.
Weak Ignition Coil: A failing coil or coil boot often causes one cylinder to break down first, and the miss may get worse during acceleration or damp weather.
Dirty or Leaking Fuel Injector: If one injector is clogged, weak, or leaking, that cylinder can run lean or rich while the others still run normally.

What a Misfire on Only One Cylinder Usually Means

When only one cylinder is misfiring, the engine computer is often telling you that the fault is not system-wide. That is why cylinder-specific misfire codes are so useful. A P0304, for example, points you toward cylinder 4, not necessarily the exact bad part.

In real-world diagnosis, ignition faults are usually the first place to look because they are common and easy to isolate. If the misfire follows a swapped plug or coil to another cylinder, you have learned a lot very quickly. That kind of part-swapping test is often more useful than guessing from symptoms alone.

If the misfire stays on the same cylinder after swapping ignition parts, the problem is more likely tied to that cylinder itself. Common examples are an injector that is not delivering fuel correctly, a small intake leak near that runner, damaged wiring to that coil or injector, or low compression from valve, ring, or head gasket trouble.

The way the misfire behaves matters. A miss that is worst at idle can point toward a fouled plug, injector imbalance, or an intake leak near one cylinder. A misfire that shows up more under load often suggests an ignition coil that can no longer make enough spark when cylinder pressure rises. A dead miss all the time raises concern for injector failure or a mechanical problem.

Possible Causes of an Engine Misfiring on One Cylinder

Worn Spark Plug

Each cylinder depends on its own plug to ignite the air-fuel mixture. If one plug is worn, fouled, cracked, or improperly gapped, that cylinder may misfire while the rest of the engine runs normally.

Symptoms to Watch For

Rough idle with a steady rhythmic miss
Misfire code that stays with the same cylinder until the plug is moved
Plug tip looks oil-fouled, carbon-fouled, or fuel-soaked
Harder starting or stumble during light acceleration

Moderate Severity

A bad plug may not seem urgent at first, but continued misfiring can overload the catalytic converter and worsen fuel economy and drivability.

How to Confirm: Remove the suspect plug and compare it to plugs from other cylinders.

Typical fix: Replace the faulty spark plug, and replace the full plug set if service interval or wear condition supports it.

Weak Ignition Coil

Modern ignition systems often give each cylinder its own coil. When one coil weakens, it may still fire at idle sometimes but break down under load, causing a cylinder-specific misfire.

Symptoms to Watch For

Misfire gets worse during acceleration or climbing hills
Misfire starts or worsens in damp weather
Cylinder code moves when the coil is swapped
Cracked coil housing or deteriorated coil boot

Moderate to High Severity

A coil failure can become a hard misfire quickly and may cause converter damage if the cylinder keeps sending unburned fuel into the exhaust.

How to Confirm: Swap the suspect coil with a known good coil from another cylinder and clear the codes.

Typical fix: Replace the failed ignition coil and any damaged coil boot.

Dirty or Leaking Fuel Injector

A restricted injector can starve one cylinder, while a leaking injector can overfuel it. Either condition disrupts combustion on that cylinder without affecting the others the same way.

Symptoms to Watch For

Misfire stays on one cylinder after plug and coil swaps
Fuel trim problems or fuel smell from the exhaust
One spark plug looks unusually white or unusually wet
Cold-start stumble that clears somewhat as the engine warms

Moderate to High Severity

A lean misfire can overheat a cylinder, while a leaking injector can wash down cylinder walls, dilute oil, and damage the catalytic converter.

How to Confirm: Listen to the injector with a mechanic's stethoscope for a regular clicking sound, verify injector pulse with a noid light or scope, and compare injector resistance to spec if applicable.

Typical fix: Clean or replace the faulty fuel injector and install new injector seals if required.

Vacuum Leak Near One Intake Runner

A small intake manifold gasket leak or crack near one runner can lean out just one cylinder enough to cause a misfire, especially at idle when manifold vacuum is highest.

Symptoms to Watch For

Misfire is worst at idle and improves off idle
Hissing noise near the intake manifold
Higher or unstable idle speed
Fuel trims show the engine adding fuel

Moderate Severity

A localized vacuum leak can usually be repaired before major damage occurs, but it can keep the engine running lean and rough if ignored.

How to Confirm: Use a smoke machine to test the intake system or carefully check for leak response around the suspect runner area with proper safety precautions.

How to Find a Vacuum Leak in Your Car

Typical fix: Replace the leaking intake gasket, cracked vacuum hose, or damaged intake component causing the air leak.

Wiring or Connector Fault at the Coil or Injector

A broken wire, poor terminal fit, corroded connector, or bad ground can interrupt spark or injector control on just one cylinder. This can create an intermittent misfire that looks like a bad part until wiring is tested.

Symptoms to Watch For

Misfire appears after engine movement or vibration
Problem changes when harness is moved
Connector shows corrosion, oil intrusion, or loose pins
New plug or coil did not fix the same cylinder

Moderate to High Severity

Electrical faults can become more frequent over time and can waste money if parts are replaced before the circuit is proven good.

How to Confirm: Inspect the harness and connector closely, then test for proper power, ground, and control signal at the suspect coil or injector.

Typical fix: Repair the damaged wiring, replace the faulty connector, or restore the affected ground or power feed.

Low Compression in One Cylinder

If one cylinder cannot seal properly because of a burned valve, worn rings, valve timing issue, or head gasket leak, it may misfire no matter how good the spark and fuel delivery are.

Symptoms to Watch For

Misfire stays on same cylinder after swapping ignition and fuel parts
Consistent roughness at idle and under load
Low power with possible puffing through intake or exhaust
Abnormal compression or leak-down result

High Severity

A mechanical problem inside the engine usually will not fix itself and can progress into major engine damage or catalyst damage if the vehicle keeps being driven misfiring.

How to Confirm: Run a compression test on all cylinders, then follow up with a leak-down test if one cylinder is low.

Typical fix: Repair the underlying mechanical fault, which may involve valve work, head gasket replacement, or internal engine repair.

How to Diagnose the Problem

Scan for trouble codes and confirm which cylinder is misfiring instead of guessing from feel alone.
Note when the misfire is worst, such as cold start, hot idle, acceleration, or wet weather.
Inspect the suspect cylinder's spark plug, coil boot, and plug well for wear, oil, water, or carbon tracking.
Swap the spark plug with another cylinder and see whether the misfire code moves.
If the misfire stays put, swap the ignition coil and clear codes again to see whether the fault follows the coil.
If ignition parts do not move the misfire, check injector operation with a listening test, noid light, resistance check, or injector swap.
Inspect nearby intake gaskets, vacuum hoses, and the runner area for a localized air leak, especially if idle is the worst condition.
Check the connector and wiring to that cylinder's coil and injector for corrosion, loose terminals, rub-through, or intermittent signal loss.
Run a compression test if the same cylinder still misfires after spark and fuel checks, then perform a leak-down test if compression is low.
If the check engine light is flashing or the engine is shaking hard, stop extended driving and diagnose the cause before converter damage occurs.

Can You Keep Driving With a One-Cylinder Misfire?

Important: The guidance below is general and cannot confirm that your specific vehicle is safe to drive. If a symptom affects braking, steering, handling, fuel, overheating, smoke, visibility, or vehicle control, treat it as potentially serious and have the vehicle inspected before continued driving when appropriate. For more context, see our Automotive Safety Disclaimer.

Whether you can keep driving depends on how severe the misfire is and what is causing it. A mild intermittent miss is very different from a hard, active misfire with a flashing check engine light.

Okay to Keep Driving for Now

A very light, occasional misfire with no flashing check engine light and no major loss of power may be drivable for a short period while you schedule diagnosis. Keep trips short, avoid hard acceleration, and do not ignore it for long.

Maybe Okay for a Very Short Distance

If the engine runs rough but still moves normally, it may be reasonable to drive only a very short distance to get home or to a shop. This applies best when the light is steady, not flashing, and the engine is not shaking violently.

Not Safe to Keep Driving

Do not keep driving if the check engine light is flashing, the engine is bucking badly, raw fuel smell is obvious, power is sharply reduced, or the vehicle may stall in traffic. Active misfires can quickly damage the catalytic converter and may indicate a serious mechanical problem.

How to Fix It

The right fix depends on what is making that one cylinder fail to burn properly. Good diagnosis matters because a one-cylinder misfire can come from a simple ignition part or from a deeper cylinder-specific engine problem.

DIY-friendly Checks

Start with code scanning, spark plug inspection, coil and plug swapping between cylinders, and a careful look for oil, moisture, or damaged connectors at the suspect cylinder.

Common Shop Fixes

Shops commonly fix one-cylinder misfires by replacing plugs or coils, servicing or replacing an injector, repairing an intake leak, or correcting damaged wiring at the coil or injector circuit.

Higher-skill Repairs

If compression is low or leak-down results point to valve, ring, or head gasket trouble, the repair usually moves into cylinder head or internal engine work that requires deeper testing and labor.

Related Repair Guides

Typical Repair Costs

Repair cost depends on the vehicle, labor rates, and what is actually causing that one cylinder to misfire. The ranges below are typical U.S. parts-and-labor estimates, not exact quotes for every engine layout.

Spark Plug Replacement

Typical cost: $120 to $350

This usually applies when the misfire is caused by a worn or fouled plug, though access can raise labor on some engines.

Ignition Coil Replacement

Typical cost: $150 to $450

A single coil is often straightforward, but price varies by engine design and whether the boot is replaced too.

Fuel Injector Cleaning or Replacement

Typical cost: $180 to $700

Cleaning is cheaper, while direct injector replacement costs more and may involve intake removal or coding procedures.

Intake Gasket or Vacuum Leak Repair

Typical cost: $150 to $600

Small hose repairs stay low, but intake manifold gasket access can push labor higher.

Wiring or Connector Repair

Typical cost: $120 to $400

This range fits localized harness or connector repairs near a coil or injector rather than full harness replacement.

Compression-related Engine Repair

Typical cost: $600 to $3,500+

Costs vary widely because valve work, head gasket repair, and internal engine damage are very different jobs.

What Affects Cost?

Engine layout and access to plugs, coils, or injectors
Local labor rates and diagnostic time required
OEM versus aftermarket ignition and fuel system parts
Whether the misfire damaged the catalytic converter
Whether the root cause is external or internal to the engine

Cost Takeaway

If the misfire follows a spark plug or coil, you are usually in the lower to middle cost range. If it stays on the same cylinder after swaps, expect more diagnostic time and a higher chance of injector, wiring, intake leak, or compression-related repair costs.

Symptoms That Can Look Similar

Parts and Tools

FAQ

Can One Bad Spark Plug Cause a Misfire on Only One Cylinder?

Yes. A single worn, fouled, cracked, or incorrectly gapped spark plug can cause a cylinder-specific misfire, and it is one of the first things worth checking.

Will a One-cylinder Misfire Always Trigger a Check Engine Light?

Not always right away, but many vehicles will log a pending or stored misfire code before the light becomes obvious. A severe active misfire often causes a flashing check engine light.

How Do I Know if It Is the Coil or the Injector?

The fastest practical test is usually to swap the coil with another cylinder and see whether the misfire follows it. If it does not, injector testing, injector swapping, and circuit checks become more important.

Can Low Compression Cause a Misfire on Just One Cylinder?

Yes. Low compression from a burned valve, worn rings, head gasket leak, or other sealing problem can leave one cylinder unable to burn the mixture properly even when spark and fuel are present.

Is It Safe to Keep Driving with One Cylinder Misfiring?

Only if the misfire is very mild and intermittent, and even then only briefly. If the engine is shaking hard or the check engine light is flashing, continued driving can damage the catalytic converter.

Final Thoughts

A one-cylinder misfire is usually most manageable when you treat it like an isolation problem instead of a mystery. Confirm the cylinder first, then start with the parts that are easiest to swap and compare, especially the spark plug and ignition coil.

If the misfire stays on the same cylinder after those basic checks, move to injector, intake leak, wiring, and compression testing. That pattern is what separates a simple tune-up fix from a deeper engine problem, and it is also what tells you how urgent the repair really is.