OBD-II Code P0307: Cylinder 7 Misfire Detected

What Does P0307 Mean?

Your vehicle's Powertrain Control Module (PCM) detected cylinder 7 is not firing correctly. This means the cylinder lacks power, causing incomplete combustion. The PCM monitors crankshaft rotational speed; a fluctuation of 2% or more between power strokes flags a misfire. This code only appears on engines with at least eight cylinders.

Technical definition: The SAE/OBD-II definition for P0307 is "Cylinder 7 Misfire Detected". 🎬 Watch: A quick breakdown of what P0307 means and how to fix it. The Powertrain Control Module (PCM) determined the crankshaft's rotational speed decreased by 2% to 10% during cylinder 7's power stroke. A fluctuation greater than 10% triggers a flashing check engine light to warn of imminent catalytic converter damage.

Can I Drive With P0307?

no_if_flashing. If the check engine light is solid, limit driving to essential short trips and avoid heavy acceleration. A persistent misfire dumps unburned fuel into the exhaust, destroying the catalytic converter. If the light flashes, pull over and stop the engine immediately. Continuing to drive damages the catalytic converter in just a few miles, turning a $50 repair into a $1,500-$3,500+ expense.

Common Causes

• Faulty Ignition Coil or Coil Pack (Very Common) — The ignition coil provides high voltage to the spark plug. A failing coil is the top cause of single-cylinder misfires and the easiest component to test.
• Worn or Fouled Spark Plug (Very Common) — An old, damaged, or carbon-fouled spark plug cannot produce a strong enough spark for proper combustion. This is the cheapest and most common fix.
• Failed AFM/MDS Lifter (Common) — On V8 engines from GM (AFM) and Ram/Dodge (MDS), cylinder deactivation lifters frequently collapse. This causes a permanent P0307 and a distinct ticking noise.
🎬 See how to diagnose a collapsed AFM lifter on a Chevy Silverado.
• Clogged or Failed Fuel Injector (Common) — A clogged or electrically failed fuel injector starves cylinder 7 of fuel, disrupting the air-fuel mixture and causing a lean misfire.
• Vacuum Leak (Less Common) — An air leak from a cracked intake manifold gasket near cylinder 7 leans out the mixture. This frequently triggers a P0171 or P0174 lean code alongside P0307.
• Low Cylinder Compression (Less Common) — Internal engine damage like a burnt valve, worn piston rings, or a blown head gasket prevents combustion. A mechanical compression test confirms this.
• Wiring Harness or Connector Fault (Rare) — A corroded or broken connector for cylinder 7's ignition coil or fuel injector interrupts the electrical signal, mimicking a failed component.
🎬 Watch this guide to identify common causes and fixes for cylinder 7 misfires.
• Faulty Powertrain Control Module (PCM) (Very Rare) — The engine computer itself fails or suffers software corruption, incorrectly reporting a misfire. Consider this only after exhaustively ruling out all other hardware.

Symptoms

• Flashing or Solid Check Engine Light — A solid light confirms a misfire. A flashing light signals a severe, catalyst-damaging misfire requiring an immediate stop.
• Rough Idle and Engine Vibration — The engine runs unevenly and shakes violently, especially when stopped at a red light.
• Loss of Power and Hesitation — The vehicle feels sluggish and stumbles during acceleration because it operates on one less cylinder.
• Fuel Smell from Exhaust — Raw gasoline odor emits from the tailpipe because unburned fuel passes straight through the dead cylinder.
• Reduced Fuel Economy — Fuel consumption spikes by 10-20% as the engine dumps extra fuel to compensate for the power loss.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Replace Ignition Coil — Parts: $50-$150, Labor: $60-$150, ~0.8 hr book time (DIY)
• Replace Spark Plugs — Parts: $40-$100, Labor: $150-$300, ~1.5 hr book time (DIY)
• Replace Fuel Injector — Parts: $100-$300, Labor: $200-$600, ~2.5 hr book time (Intermediate)
• Repair AFM/MDS Lifters and Camshaft — Parts: $800-$1500, Labor: $2200-$4500, ~18 hr book time (Professional)
• Intake Manifold Gasket Replacement — Parts: $50-$150, Labor: $300-$600, ~3.5 hr book time (Intermediate)

DIY vs Professional

• Replace Ignition Coil — Beginner:
  Tools: 10mm socket, ratchet.
• Replace Spark Plugs — Beginner:
  Tools: Ratchet, extensions, spark plug socket, torque wrench.
• Replace Fuel Injector — Beginner:
  Tools: Ratchet set, fuel line disconnect tool, torque wrench.
• Repair AFM/MDS Lifters — Beginner:
  Tools: Full engine tool set, torque-to-yield sockets, timing gear.

Used vs. New Parts: Buying Guide

When a used part is worth it: Never buy used spark plugs or ignition coils. They are cheap wear items. A used coil will fail quickly, doubling your labor costs.

Donor-vehicle mileage cap: roughly under 10000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Only buy a used OEM coil if new OEM is backordered, and only from a verified low-mileage wreck.

Decision logic:

• If The part is a spark plug or ignition coil → Always buy new OEM or premium aftermarket (NGK, Denso).
• If The part is a fuel injector → Buy new or professionally remanufactured. Avoid junkyard injectors.

Warranty tradeoff: Used parts carry a 30-day warranty. New OEM coils carry a 1-year to lifetime warranty.

Worst-case if a used part fails: $300 to re-diagnose and replace a junkyard coil that failed after two weeks.

What Happens If You Wait — Timeline

1. 0-1 month: Solid Check Engine Light. Minor hesitation on acceleration. Fuel economy drops slightly. (MPG impact: 1-5%% · Added cost: $50 in wasted fuel)
2. 1-3 months: Light flashes during heavy acceleration. Raw fuel superheats the catalytic converter substrate. (MPG impact: 5-10%% · Added cost: $150 in wasted fuel. Converter life shortened.)
3. 3-6 months: Catalytic converter melts and clogs. Vehicle loses severe power and stalls at stops. (MPG impact: 10-20%% · Added cost: $1,500 - $3,500 for catalytic converter replacement.)
4. 6+ months: Clogged exhaust creates extreme backpressure, burning exhaust valves. Unburned fuel washes oil from cylinder walls, scoring pistons. (MPG impact: 20-35%+% · Added cost: $5,000+ for complete engine replacement.)

Cost of Not Fixing It

• Immediate (0-1 month): Reduced fuel economy, rough idle, and automatic emissions test failure. (Added cost: $50-$150 in wasted fuel)
• Short Term (1-6 months): Unburned fuel superheats and melts the catalytic converter honeycomb. (Added cost: $1,500-$3,500 for catalytic converter replacement)
• Long Term (6+ months): Fuel washes oil from cylinder walls, scoring pistons and burning exhaust valves. (Added cost: $5,000+ for engine replacement)

Diagnosis Steps

1. Read Codes and Freeze Frame Data
   Use an OBD-II scanner to confirm P0307. Check for related codes (P0300, P0171, P0207) which pinpoint systemic, lean, or electrical issues. Note the freeze frame data to replicate conditions during testing.
   Tools: OBD-II Scanner (Beginner)
2. Swap the Ignition Coil
   Swap the cylinder 7 ignition coil with cylinder 5. Clear the codes and drive the vehicle. If the code changes to P0305, the ignition coil is dead. Replace it.
   Tools: Socket/ratchet set (Beginner)
3. Swap the Spark Plug
   If the misfire stays on cylinder 7, swap the spark plug with another cylinder. If the code follows the plug, replace all spark plugs. Inspect the removed plug for oil or carbon fouling.
   Tools: Spark plug socket, ratchet, extension (Intermediate)
4. Inspect the Fuel Injector
   Place a mechanic's stethoscope against the cylinder 7 fuel injector while the engine idles. You must hear a consistent, rhythmic clicking. Silence indicates a dead injector or wiring fault.
   Tools: Mechanic's stethoscope (Intermediate)
5. Check for Vacuum Leaks
   Spray brake cleaner around the intake manifold gasket near cylinder 7 while the engine idles. A sudden change in RPM confirms a vacuum leak.
   Tools: Brake cleaner or smoke machine (Intermediate)
6. Test the Fuel Injector Circuit
   Disconnect the injector. Measure internal resistance with a multimeter (expect 11-14 Ohms). Plug a noid light into the harness and crank the engine; a flashing light confirms the PCM is sending the pulse signal.
   Tools: Multimeter, Noid Light Kit (Advanced)
7. Perform a Mechanical Compression Test
   Remove the spark plug and thread in a compression tester. Crank the engine. A healthy V8 reads 125-160 PSI. A reading below 100 PSI or 15% lower than other cylinders confirms internal mechanical failure (burnt valve, bad rings, collapsed lifter).
   Tools: Compression tester kit (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 180-210°F (Fully warmed up)
• RPM: 1500-3000 (Cruise / steady throttle / light acceleration)
• Engine Load: 20-50% (Maintaining speed on a flat road or slight incline)
• Vehicle Speed: 45-65 mph (Highway or arterial road driving)

Related Codes

• P0300 — Random/Multiple Cylinder Misfire. Indicates a systemic issue (fuel pressure, vacuum leak) rather than a single bad coil or plug on cylinder 7.
• P0207 — Injector Circuit Malfunction - Cylinder 7. Confirms the misfire is caused by a dead fuel injector or broken injector wiring.
• P0171/P0174 — System Too Lean. Proves the misfire is caused by unmetered air (vacuum leak) or starved fuel (clogged injector), not a spark issue.

Climate & Environmental Factors

• High Humidity / Rain: Moisture exposes microscopic cracks in aging ignition coils. Electricity grounds out through the moisture instead of jumping the spark plug gap, causing wet-weather misfires.
• Cold Weather: Cold starts require a richer fuel mixture. A partially clogged injector fails to deliver enough fuel in dense, cold air, causing a misfire that disappears once the engine warms up.

How to Talk to a Mechanic About This Code

Say this: "I have a P0307 code on my [Year, Make, Model]. Please start by swapping the coil and plug on cylinder 7 to see if the misfire moves. If it doesn't, run a compression test before replacing any parts."

This directs the mechanic to perform the cheapest, most definitive tests first, preventing them from firing the 'parts cannon' at your expense.

Avoid saying:

• 'Just fix the misfire.'
• 'My check engine light is on, can you look at it?'
• 'I think I need a new fuel injector.'

Questions to ask before authorizing the repair:

• Did you swap the coil to another cylinder to confirm the misfire moved?
• What were the exact PSI readings from the compression test?
• Are you using OEM or aftermarket ignition parts?

Where to Take It: Dealer vs Independent vs Chain

• Dealer:
  Best for: Vehicles under powertrain warranty, Diagnosing complex AFM/MDS lifter failures on GM and Ram trucks
  Downsides: Highest labor rates ($150-$250/hr), Will push for full engine replacement rather than targeted internal repairs (Typical cost: +40% vs. baseline)
• Independent Shop: The best choice. A competent independent shop easily handles ignition swaps, compression tests, and valvetrain repairs for thousands less than a dealer.
  Best for: Out-of-warranty vehicles, Cost-effective diagnosis of coils, plugs, and injectors, Performing AFM/MDS delete kits
  Downsides: Diagnostic capabilities vary widely by technician skill (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid for initial diagnosis. They frequently replace spark plugs without fixing the root cause.
  Best for: You already diagnosed a bad coil yourself and just need it bolted on
  Downsides: High pressure to upsell unnecessary fuel system flushes, Lack the expertise to diagnose internal engine lifter failures (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the repair requires a $3,500+ valvetrain rebuild (lifters/camshaft) and exceeds 40% of the vehicle's value, sell the vehicle as-is.

• Car worth $8000, fix is $4000: Walk away. Spending 50% of the truck's value on a lifter repair is a poor investment. Trade it in.
• Car worth $15000, fix is $250: Fix it. Replacing an ignition coil and spark plugs is standard maintenance.

What Scan Tool You Need for This Code

Minimum: A scanner that reads Mode 6 data to show live misfire counts per cylinder.

A $20 reader only shows 'P0307'. It cannot show if cylinder 7 is misfiring 5 times per minute or 500 times per minute, which is critical for verifying if a repair worked.

Budget: BlueDriver Pro (~$119) — Connects to your smartphone, reads freeze-frame data, and accesses Mode 6 live misfire counts.

Mid-range: Innova 5610 (~$350) — Provides bidirectional controls to manually command the cylinder 7 fuel injector to click, testing the electrical circuit instantly.

Professional: Autel MaxiCOM MK808 (~$500) — Graphs live fuel trims, O2 sensor data, and misfire counts simultaneously to diagnose complex lean-condition misfires.

Rent vs buy: Buy the BlueDriver. AutoZone loaner scanners often block live data viewing, making them useless for verifying misfire repairs.

How to Clear the Code After You Fix It

1. Fix the root cause of the misfire
2. Use the scanner to clear the P0307 code
3. Drive the vehicle to reset readiness monitors

Drive cycle (~30 minutes): Cold start, idle for 3 minutes, drive in stop-and-go traffic for 10 minutes, then maintain 55-60 mph on the highway for 15 minutes.

Readiness monitors affected: Misfire Monitor, Catalyst Monitor, Oxygen Sensor Monitor

Before emissions retest: drive at least 50-100 miles to fully set monitors.

Watch out for:

• Disconnecting the battery clears the code but resets all monitors to 'Not Ready', guaranteeing an emissions failure.
• The code returns immediately if you only replaced the spark plug but the lifter is collapsed.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: Automatic failure. After repair, all OBD readiness monitors must read 'Ready'. You must drive 50-100 miles before retesting.
• New York: An illuminated Check Engine Light guarantees failure. Clearing the code in the parking lot results in a 'Not Ready' rejection.
• Texas: Automatic failure in emissions counties. Only one readiness monitor can be 'Not Ready' to pass.

Most Commonly Affected Vehicles

• Chevrolet/GMC Silverado/Sierra 1500 (5.3L) (2007-2019) — Highly prone to failed Active Fuel Management (AFM) lifters. Cylinder 7 is an AFM cylinder. A ticking noise confirms lifter failure (TSB 19-NA-219).
• Ram 1500 (5.7L HEMI) (2009-2023) — Notorious for Multi-Displacement System (MDS) lifter failure, destroying the camshaft. Widely known as the 'Hemi Tick'.
• Ford F-150 (5.0L) (2011-2014) — Prone to burnt intake valves causing low compression on cylinder 7. Requires a cylinder head rebuild.
• BMW X5, 7 Series (V8) (2005-2015) — Commonly experience P0307 due to aging ignition coils. Cylinder 7 access is difficult, increasing labor costs.

Manufacturer-Specific Notes

• General Motors (Chevrolet/GMC): A P0307 on a 5.3L V8 is almost always a collapsed AFM lifter. Listen for a ticking noise from the driver's side valve cover.
• Ram/Dodge/Chrysler (Stellantis): The 'Hemi Tick' on 5.7L engines pairs perfectly with P0307, indicating a destroyed MDS lifter and scored camshaft lobe.
• Ford: On 2011-2014 5.0L V8s, a persistent P0307 that ignores new coils and plugs is a burnt intake valve. Run a compression test immediately.

Real Owner Stories

2013 Ford F-150 5.0L - The Burnt Valve

Owner experienced an intermittent P0307. Swapping coils and plugs changed nothing.

Outcome: A compression test revealed 70 PSI in cylinder 7. The diagnosis was a burnt intake valve, a known flaw for 2011-2014 5.0L engines, requiring a cylinder head rebuild.

Lesson: If new plugs and coils don't fix a Ford 5.0L misfire, run a compression test immediately before wasting money on fuel injectors.

2019 Ram 1500 5.7L - The Misleading Misfire

Flashing check engine light with codes P0307 and P0171 (Bank 1 Lean). Owner feared a $4,000 lifter failure.

Outcome: Removed and flushed the fuel injectors. Black gunk washed out of injector 7. Reinstalled, and the engine ran perfectly.

Lesson: A P0307 paired with a lean code (P0171) guarantees a fuel or air issue, not a mechanical lifter failure. Clean injectors first.

2016 Chevrolet Silverado 5.3L - Classic AFM Failure

Persistent P0307 misfire accompanied by a loud ticking noise from the driver's side valve cover.

Outcome: Removed the valve cover and observed a stationary rocker arm on cylinder 7 while cranking. Confirmed a collapsed AFM lifter requiring a $3,500 repair.

Lesson: On GM V8s, a P0307 plus a ticking noise is the definitive signature of a collapsed AFM lifter.

How to Prevent This Code From Triggering

• Follow Spark Plug Replacement Intervals (Every 60,000-100,000 miles) — Worn spark plug gaps require higher voltage, burning out ignition coils and causing misfires. Fresh plugs are the ultimate misfire prevention.
• Change Engine Oil with Full Synthetic (Every 5,000 miles) — Dirty oil clogs the microscopic passages in AFM/MDS cylinder deactivation lifters, causing them to collapse and trigger P0307.
• Install an AFM/MDS Disabler (One-time installation) — Plugging an electronic disabler into the OBD-II port prevents GM and Ram V8s from deactivating cylinders, saving the fragile lifters from premature failure.

Frequently Asked Questions

What does the '7' in P0307 mean?

The '07' specifies the misfire is happening in the cylinder numbered '7' by the manufacturer. It does not refer to the firing order.

Why is my check engine light flashing?

A flashing light means raw fuel is dumping into the exhaust and melting your catalytic converter. Pull over and shut off the engine immediately. Driving further guarantees a $2,000+ repair bill.

I replaced the spark plug and coil, but P0307 came back. What now?

Check the fuel injector and its wiring for faults. If fuel delivery is fine, perform a mechanical compression test to check for a burnt valve or collapsed lifter.

I have a Ram Hemi with P0307 and a ticking noise. Is it the 'Hemi Tick'?

Yes, it is highly probable. A persistent P0307 paired with a tick strongly points to a failed MDS lifter and damaged camshaft, requiring a major engine repair.

What is an AFM/MDS delete kit?

It is a mechanical conversion that replaces failure-prone cylinder deactivation lifters with standard, durable V8 lifters. This permanent fix prevents future P0307 codes related to valvetrain collapse.

Will a P0307 code fail an emissions test?

Yes. An active P0307 code automatically fails any state emissions test because unburned fuel drastically increases hydrocarbon output.

How do I find cylinder 7 on my engine?

Search online for your specific vehicle's 'cylinder location diagram'. On most American V8s (GM, Ford, Ram), cylinder 7 is the rearmost cylinder on the driver's side.

Key Takeaways

• A P0307 code means cylinder 7 is misfiring, reducing fuel economy by up to 15% and risking severe exhaust damage.
• A flashing check engine light means raw fuel is melting your catalytic converter—pull over immediately to avoid a $1,500 to $3,500 repair bill.
• Diagnose the issue for free by swapping the cylinder 7 ignition coil with cylinder 5; if the code changes to P0305, you only need a $50 to $150 replacement coil.
• On GM 5.3L and Ram 5.7L V8s, a P0307 paired with a ticking noise confirms a collapsed AFM/MDS lifter, requiring a $3,000 to $7,000 valvetrain rebuild.