Same Cylinder Keeps Misfiring - Top Causes, Fixes & What to Do

Certified Professional Automotive Mechanic – Owner and Editor of VehicleRuns

Last Updated: September 8, 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 same cylinder keeps misfiring, that usually means the problem is not random. A repeated misfire on one cylinder points to something local to that cylinder, such as its spark plug, ignition coil, injector, wiring, intake runner, or mechanical condition.

This pattern matters because a single-cylinder misfire is diagnosed differently than a general rough-running problem. The key clues are when it happens, whether the misfire moves when parts are swapped, whether the check engine light is flashing, and whether that cylinder shows signs of weak compression.

Some causes are fairly minor and inexpensive. Others can damage the catalytic converter or point to internal engine trouble, so the smartest approach is to narrow the fault path early instead of replacing parts at random.

Start by separating a simple cylinder-specific fault from a deeper mechanical one. The most useful clues are whether the misfire moves when you swap parts, when the engine runs worst, and whether the check engine light is flashing.

What you notice	Most likely cause	What to check first	Urgency
Misfire moves after swapping coil or plug	Faulty ignition component	Swap the coil or plug to another cylinder and rescan	Diagnose soon
Same cylinder misfires mostly at idle	Local vacuum leak	Inspect the intake gasket, runner, and nearby vacuum hoses	Can worsen
Same cylinder misfires under load	Weak coil or low compression	Check plug condition, then run compression or leak-down testing	Can worsen
Fuel smell, wet plug, cylinder not contributing	Leaking or stuck injector	Check injector pulse and compare injector resistance or balance	Can worsen
Flashing check engine light and severe shaking	Active damaging misfire	Stop driving and scan for the affected cylinder code	Stop driving

Best first move: Confirm which cylinder is affected, then use part-swapping and cylinder-specific checks before assuming a major engine problem.

Safety note: Do not keep driving with a flashing check engine light, raw fuel smell, or severe shaking, because an ongoing misfire can overheat and damage the catalytic converter.

Table of Contents

Most Common Causes of the Same Cylinder Misfiring

In real-world cases, a repeated misfire on the same cylinder is most often caused by a fault tied directly to that cylinder. The three most common starting points are below, and a fuller cause list appears later in the article.

Faulty Spark Plug or Ignition Coil: When one cylinder keeps setting the same misfire code, a weak plug or coil is one of the most common causes, especially if the misfire moves after swapping parts.
Dirty or Failing Fuel Injector: A restricted, leaking, or electrically failed injector can make one cylinder run lean or rich enough to misfire while the others run normally.
Low Compression in That Cylinder: If ignition and fuel checks pass, a burnt valve, worn rings, or head gasket problem can leave one cylinder unable to burn the mixture consistently.

What the Same Cylinder Misfiring Usually Means

When the same cylinder keeps misfiring, think locally before thinking globally. A random misfire across several cylinders often points to fuel quality, airflow, or system-wide control issues, but one cylinder repeating usually means that one cylinder has a unique problem.

The most useful split is whether the misfire follows a swapped part. If you move the coil or spark plug to another cylinder and the misfire code follows it, you have a strong ignition clue. If the misfire stays on the same cylinder, the problem is more likely the injector, wiring, intake leak at that runner, or the cylinder’s mechanical health.

When the engine runs worst also matters. A misfire that shows up mostly at idle often fits a small intake leak near one runner because vacuum is highest at idle. A misfire that gets worse under load often points more toward a weak coil, worn plug, or low compression that only shows up when cylinder pressure rises.

If the engine shakes badly, the check engine light flashes, or the exhaust smells strongly of raw fuel, the misfire is active enough to matter right now. In that situation, the goal is not just comfort. It is to prevent catalyst damage and avoid turning a simpler repair into a more expensive one.

Possible Causes of a Repeated Misfire on One Cylinder

Faulty Spark Plug or Ignition Coil

Each cylinder has its own ignition path. If the plug is fouled, cracked, worn, or fuel-soaked, or the coil cannot deliver strong spark under the right conditions, that cylinder can misfire repeatedly while the others continue to run normally.

Symptoms to Watch For

Misfire gets worse under acceleration or load
Misfire code follows the coil or plug after swapping
Plug from the bad cylinder looks unusually fouled or wet
Rough idle with little or no injector-related fuel smell

Moderate Severity

A single bad ignition part is usually straightforward to fix, but driving too long with an active misfire can damage the catalytic converter.

How to Confirm: Remove and inspect the spark plug from the affected cylinder for fouling, cracked porcelain, excess gap, oil, or fuel wetness.

Typical fix: Replace the faulty spark plug, ignition coil, or both, and replace related tune-up parts if the rest are similarly worn.

Dirty or Failing Fuel Injector

That cylinder depends on its injector to deliver the right amount of fuel with the right spray pattern. If the injector is clogged, sticking, leaking, or electrically dead, the cylinder can run too lean or too rich and misfire over and over.

Symptoms to Watch For

Misfire stays on the same cylinder after coil and plug swaps
Raw fuel smell or wet spark plug on the affected cylinder
Cylinder contribution is weak even though spark is present
Misfire may worsen at idle or during transition throttle

Moderate to High Severity

A leaking injector can wash down the cylinder wall, dilute engine oil, and overheat the catalytic converter if left unresolved.

How to Confirm: Use a scan tool to identify the cylinder, then verify injector pulse with a noid light or lab scope.

Typical fix: Replace or professionally clean the affected injector and install new seals where required.

Low Compression in That Cylinder

A cylinder needs enough sealing to build pressure and burn the air-fuel charge correctly. Burnt valves, worn piston rings, head gasket leakage, or other internal mechanical damage can leave one cylinder too weak to fire consistently.

Symptoms to Watch For

Misfire stays on the same cylinder no matter which parts are swapped
Engine has a steady shake at idle and under load
Low power with a puffing intake or exhaust note
Compression test result is much lower than neighboring cylinders

High Severity

Mechanical compression loss is a more serious condition because the repair is usually deeper, and continued driving can worsen engine damage.

How to Confirm: Run a compression test on all cylinders and compare readings.

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

Wiring, Connector, or Electrical Ground Fault

Even a good coil or injector will misfire if it is losing command, power, or ground at that cylinder. Heat, vibration, oil contamination, or stretched harness wiring can create an intermittent or constant one-cylinder fault.

Symptoms to Watch For

Misfire stays on the same cylinder despite known-good swapped parts
Misfire changes when the harness is moved
Corrosion, broken insulation, or loose terminals at the coil or injector connector
Intermittent misfire that comes and goes with engine movement or heat

Moderate Severity

The fault itself may be minor, but intermittent wiring problems often waste time and can become no-start or catalyst-damaging misfires if ignored.

How to Confirm: Back-probe the coil or injector connector and compare power, ground, and control signals to a good cylinder.

Typical fix: Repair damaged wiring, clean or replace the connector, and restore the affected power or ground path.

Intake Manifold Gasket Leak at One Runner

A small leak near one intake runner can feed extra unmetered air to just one cylinder. That cylinder then runs leaner than the others, which is why the misfire often stays tied to the same cylinder and may be strongest at idle.

Symptoms to Watch For

Misfire is worse at idle than at higher rpm
Fuel trims may show lean correction
Hissing sound near the intake manifold area
Misfire remains on one cylinder after ignition parts test good

Moderate Severity

A runner leak usually will not destroy the engine immediately, but it can create a persistent lean misfire and driveability problems.

How to Confirm: Use a smoke machine or a careful intake leak test around the suspect runner and gasket area while monitoring idle quality or fuel trims.

How to Find a Vacuum Leak in Your Car

Typical fix: Replace the leaking intake manifold gasket or damaged vacuum fitting and reseal the affected area.

Oil Fouling From Valve Cover Gasket Tube Seal or Internal Oil Control Problem

Some engines allow oil to enter a spark plug tube or foul one cylinder’s plug more than the others. Once the plug is oil-soaked, spark quality drops and that same cylinder may keep misfiring even after the code is cleared.

Symptoms to Watch For

Oil found in the spark plug well or on the plug threads
Misfire returns quickly after installing an old contaminated coil boot
Burning oil smell from the top of the engine
Affected plug is darker and dirtier than the rest

Moderate Severity

This is often repairable without major engine work, but oil contamination will keep ruining ignition performance until the leak source is fixed.

How to Confirm: Remove the coil and plug from the misfiring cylinder and inspect the plug well and plug body for fresh oil contamination.

Typical fix: Replace the leaking valve cover gasket or tube seals, clean the plug well, and install a new plug and coil boot if contaminated.

How to Diagnose the Problem

Confirm the exact misfiring cylinder with a scan tool and note whether the code is current, pending, or returning immediately after clearing.
Pay attention to when the misfire is worst, such as idle, cold start, light throttle, or heavy load, because that pattern changes the likely cause.
Inspect the spark plug and ignition coil on the affected cylinder first, especially if they are old or the plug shows fouling, oil, or fuel wetness.
Swap the coil or spark plug with a different cylinder and rescan after a short run. If the misfire moves, the swapped part is your answer.
If the misfire stays put, check the injector on that cylinder for pulse, connector condition, and resistance or balance compared with the others.
Inspect the wiring harness and connectors for the coil and injector, looking for corrosion, loose terminals, melted insulation, or rub-through spots.
If the misfire is strongest at idle, look for a cylinder-specific vacuum leak or intake manifold gasket leak near that runner.
Run a compression test if ignition and fuel checks do not move the diagnosis forward, and follow with a leak-down test if compression is low.
Check for oil contamination in the plug well or on the plug, especially on engines known for valve cover tube seal leaks.
If all basic checks pass, move to deeper electrical signal testing or professional diagnosis for control-side issues and less common internal faults.

Can You Keep Driving If the Same Cylinder Keeps Misfiring?

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 active the misfire is and what is causing it. A mild intermittent misfire is different from a dead cylinder with a flashing check engine light.

Okay to Keep Driving for Now

Maybe, if the misfire is very light, the check engine light is not flashing, power loss is minor, and the vehicle only needs a short trip to get diagnosed. Even then, avoid hard acceleration and do not postpone the repair.

Maybe Okay for a Very Short Distance

A short drive may be possible if the engine runs rough but remains stable and you are heading directly to a shop or safe place. Keep speeds low, avoid heavy throttle, and stop if the shaking worsens or the light starts flashing.

Not Safe to Keep Driving

Do not keep driving if the check engine light is flashing, the engine is shaking badly, the exhaust smells strongly of raw fuel, the vehicle lacks power in traffic, or you suspect internal engine damage. In those cases, continued driving can damage the catalytic converter or worsen the engine fault.

How to Fix It

The right fix depends on why that cylinder is misfiring. A one-cylinder misfire is often solved by correcting the specific failed part for that cylinder, but the repair path changes a lot once compression or wiring problems enter the picture.

DIY-friendly Checks

Start with cylinder confirmation, spark plug inspection, coil and plug swapping, visual harness inspection, and checking for oil contamination in the plug well. These steps often narrow the problem without major disassembly.

Common Shop Fixes

Typical shop repairs include replacing spark plugs or coils, replacing a faulty injector, resealing an intake manifold leak, or repairing a damaged connector or short harness section.

Higher-skill Repairs

Compression loss, leak-down diagnosis, valve problems, head gasket issues, or control-side electrical faults usually require deeper testing and more advanced repair work.

Related Repair Guides

Typical Repair Costs

Repair cost depends on the vehicle, labor rates, and the actual reason that cylinder keeps misfiring. The ranges below are typical U.S. parts-and-labor estimates, not exact quotes for every engine layout.

Spark Plug Replacement for the Affected Cylinder

Typical cost: $100 to $250

This is common when the plug is fouled, worn, or oil-soaked, though labor can rise on hard-to-reach engines.

Ignition Coil Replacement

Typical cost: $150 to $400

Cost depends on coil design, whether one coil or several are replaced, and how accessible the cylinder is.

Fuel Injector Replacement

Typical cost: $250 to $700

This usually applies when the injector has failed electrically, is leaking, or fails a balance test.

Wiring or Connector Repair at Coil or Injector

Typical cost: $150 to $450

Minor terminal repair is cheaper, while harness splicing or hard-to-access damage pushes cost upward.

Intake Manifold Gasket Repair

Typical cost: $250 to $700

A localized runner leak is often moderate in cost, but labor varies widely by engine layout.

Compression-related Engine Repair

Typical cost: $600 to $3,500+

Valve work, head gasket repair, or internal engine damage creates the widest cost range and usually the highest bill.

What Affects Cost?

Engine layout and how hard the affected cylinder is to access
Whether the fault is ignition, fuel, wiring, intake, or internal engine damage
OEM versus aftermarket parts choice
How long the misfire has been present and whether it damaged the catalytic converter
Local labor rates and diagnostic time needed

Cost Takeaway

If the misfire moves when you swap a coil or plug, cost usually stays in the lower repair tiers. If the misfire stays on the same cylinder after ignition parts test good, expect mid-range injector, intake, or wiring costs. Low compression or leak-down failure is where the estimate often jumps sharply.

Symptoms That Can Look Similar

Parts and Tools

FAQ

Why Does the Same Cylinder Keep Misfiring Even After I Changed the Spark Plug?

Because the spark plug is only one part of that cylinder’s ignition and combustion path. If the same cylinder still misfires, the coil, injector, wiring, intake leak, or compression on that cylinder may be the real problem.

If I Swap the Coil and the Misfire Stays on the Same Cylinder, What Should I Check Next?

Move to fuel, air, and mechanical checks on that cylinder. A common next path is injector pulse or balance testing, connector and harness inspection, then compression or leak-down testing if ignition parts do not move the fault.

Can a Bad Injector Cause Only One Cylinder to Misfire?

Yes. A clogged, leaking, or electrically failed injector can affect just one cylinder, which is why a repeated misfire on the same cylinder often leads back to injector testing after basic spark checks.

Will a Vacuum Leak Cause One-cylinder Misfire or All-cylinder Roughness?

Either is possible, depending on where the leak is. A leak near one intake runner or gasket area can lean out one cylinder more than the others and repeatedly trigger the same cylinder misfire, especially at idle.

How Serious Is a Repeated Misfire on One Cylinder?

It ranges from moderate to serious. A bad plug or coil is usually manageable if caught early, but a flashing check engine light, raw fuel, or low compression means you should treat it as urgent and avoid continued driving.

Final Thoughts

A repeated misfire on the same cylinder usually rewards a focused diagnosis. Start with the obvious cylinder-specific items first, especially the plug, coil, injector, connector, and intake leak possibilities, then move to compression testing if the fault refuses to move.

The big mistake is guessing and replacing parts without proving the pattern. If the misfire moves with a swapped part, you have a strong answer. If it stays locked to one cylinder, the issue is deeper and should be treated sooner rather than later, especially if the check engine light is flashing.