# P0307: Cylinder 7 Misfire Detected **Verdict:** Drive to a shop this week Ignition and misfire - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $150-$4,500 - **Urgency:** This week - **Most likely:** Spark plug or ignition coil on cylinder 7 - **DIY?:** Steps 1-3 ## Quick answer P0307 means the engine computer has detected that cylinder 7 is misfiring, so it is not making its share of power. This code only appears on engines with seven or more cylinders, almost always a V8. A worn spark plug or failing ignition coil is the usual cause, but on some GM and Chrysler V8s a collapsed cylinder-deactivation lifter is a known suspect. ## What does P0307 mean? P0307 needs at least seven cylinders, so it shows up on V8, V10 and V12 engines. Where cylinder 7 sits depends on the maker. On GM V8s, including the small-block truck engines, odd-numbered cylinders run down the driver side, so cylinder 7 is the rear driver-side cylinder near the firewall. Chrysler Hemi V8s use the same layout. Ford's modular and Coyote V8s number 5 through 8 down the driver side, making cylinder 7 the third from the front on that side. The computer watches crankshaft speed and pins any slowdown on a cylinder using the firing order and camshaft signal. P0307 sets when cylinder 7 misfires often enough to raise emissions, usually confirmed on two drive cycles, or badly enough to threaten the catalytic converter, which flashes the light at once. On many GM and Chrysler V8s with cylinder deactivation, cylinder 7 is one of the four that shut off at cruise, which adds a mechanical cause to check. ## What are the symptoms of P0307? - Check engine light on, or flashing under acceleration - Shaking or uneven idle, sometimes felt through the seat - Loss of power or a stumble when towing or climbing hills - Ticking noise from the engine if a lifter has failed - Lower fuel economy than usual ## What causes P0307? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Worn or fouled spark plug in cylinder 7** (most common). Plugs wear and their gap widens until the coil can no longer fire them under load. Rear cylinders near the firewall are awkward to reach, so their plugs are sometimes skipped or poorly fitted. Oil from a leaking valve cover gasket can also foul the plug. If plugs are past their interval, replace the full set first. 2. **Failing ignition coil or plug wire on cylinder 7** (common). Coils break down from heat and vibration, and cylinder 7 often sits in a hot spot at the back of the engine. On engines with short plug wires, a wire resting on the exhaust manifold can burn through and arc. Swap it with a neighbor on the same bank and drive; if the misfire moves, replace that part. 3. **Collapsed cylinder-deactivation lifter or worn cam lobe** (less common). Many GM V8s with Active Fuel Management and Chrysler Hemis with MDS shut off cylinders 1, 4, 6 and 7 at light cruise using special lifters. These lifters can stick or collapse, especially with low or neglected oil, causing a steady misfire and a tick. A compression test, valve-motion check or relative compression test helps confirm it. 4. **Faulty cylinder 7 fuel injector** (less common). A clogged injector starves cylinder 7 and misfires mostly at idle, while a leaking one floods it, often causing a rough start after the car sits. Injector problems become more likely on high-mileage engines and on direct-injection V8s. A shop can run an injector balance test, check the electrical pulse or swap injectors to see whether the misfire follows. 5. **Vacuum leak or low compression on cylinder 7** (rare). A cracked intake gasket near the port, a burnt valve, worn rings or a head gasket leak can all make cylinder 7 misfire regardless of new ignition parts. Overheated or oil-burning engines are the most likely candidates. A smoke test finds intake leaks, and compression and leak-down tests show whether the cylinder itself is sealing properly. ## How do you diagnose P0307? 1. Read all codes and freeze-frame data, noting whether the misfire happens at idle, cruise or under load. 2. Locate cylinder 7 for your engine from a service manual, since numbering differs between makers. 3. Pull the cylinder 7 spark plug and check its wear, gap and any oil or carbon fouling. 4. Swap the cylinder 7 coil or plug wire with a neighbor, clear codes and see whether the misfire moves. 5. If ignition and fuel check out, run a compression test and listen for lifter noise on cylinder-deactivation engines. ## How do you fix P0307, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace spark plugs (full V8 set) | $200-$600 | Some Ford three-valve V8s need special plug removal and sit at the top. | | Replace cylinder 7 ignition coil or plug wire | $150-$400 | Fit a heat sleeve or reroute any wire that touched the manifold. | | Replace cylinder 7 fuel injector | $250-$750 | Direct-injection engines cost more. | | Replace failed deactivation lifters and camshaft | $2,000-$4,500 | A major job, usually involving cylinder head removal on GM V8s. | Full price breakdowns: [spark plug replacement cost](/cost/spark-plug-replacement), [ignition coil replacement cost](/cost/ignition-coil-replacement), [fuel injector replacement cost](/cost/fuel-injector-replacement). ## Is it safe to drive with P0307? > **Drive to a shop this week.** With a steady light, drive gently to a shop and avoid towing or hard acceleration. If the check engine light flashes, slow down and stop driving as soon as it is safe, because heavy misfires can overheat and destroy the catalytic converter on that bank. ## Will P0307 fail an emissions test? P0307 with the check engine light on fails an OBD-based emissions test in most states. Misfires send unburned fuel into the exhaust, raising hydrocarbon emissions and risking damage to the converter on that bank, which can later set P0420 or P0430. The misfire monitor rechecks quickly after a repair, but other monitors need several days of driving. ## After the repair: clearing P0307 Clear the code and watch the cylinder 7 misfire counter on a scan tool at idle, steady cruise and under light load. On cylinder-deactivation engines, include some light highway cruising so the system switches modes. Counts should stay near zero. If the light stays off through a week of mixed driving, including any towing you normally do, the repair worked. ## How to prevent P0307 - Replace spark plugs at the owner's manual interval and make sure rear plugs are not skipped. - Change oil on time with the specified grade, especially on cylinder-deactivation V8s. - Keep plug wires clipped away from exhaust manifolds and replace any with scorched boots. - Fix valve cover gasket leaks before oil reaches spark plug wells and coils. - Deal with a steady misfire quickly so the catalytic converter is not damaged. ## Codes often seen with P0307 - [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected - [P0308](/codes/p0308): Cylinder 8 Misfire Detected - [P0305](/codes/p0305): Cylinder 5 Misfire Detected - [P0430](/codes/p0430): Catalyst System Efficiency Below Threshold (Bank 2) - [P0420](/codes/p0420): Catalyst System Efficiency Below Threshold (Bank 1) ## Frequently asked questions ### Can I drive with a P0307 code? Only gently, and only if the check engine light is steady. A flashing light means the misfire is severe enough to damage the catalytic converter, so stop driving and arrange a tow. With a steady light, drive directly to a shop, and avoid towing, hard acceleration and long highway trips. ### Where is cylinder 7 on a V8? It depends on the maker. On GM and Chrysler Hemi V8s, cylinder 7 is the rear cylinder on the driver side, near the firewall. On Ford modular and Coyote V8s it is the third cylinder from the front on the driver side. Check a service manual for your exact engine. ### How much does it cost to fix P0307? Most P0307 repairs cost $150 to $750 at an independent shop. A full set of V8 spark plugs runs $200 to $600, one coil or wire $150 to $400 and a fuel injector $250 to $750. A failed cylinder-deactivation lifter is far more, about $2,000 to $4,500. ### Is P0307 caused by AFM lifter failure? It can be on GM V8s with Active Fuel Management and Chrysler Hemis with MDS, where cylinder 7 is one of the cylinders that deactivate. A collapsed lifter often causes a ticking sound and a misfire that a new plug or coil does not fix. Rule out ignition parts first, then test compression. ### Can I fix P0307 myself? Often yes, if the cause is a spark plug, coil or plug wire. Rear cylinders near the firewall can be tight to reach, but swapping a coil with a neighbor to see if the misfire moves is a simple, free test. Injector, compression and lifter work are best left to a shop. ### What is the difference between P0307 and P0300? P0307 names cylinder 7 specifically, so start with parts that serve only that cylinder: its plug, coil, wire and injector. P0300 means misfires are random or spread across several cylinders, pointing to shared causes such as fuel pressure or a vacuum leak. Both together mean cylinder 7 is worst. ### Will P0307 damage my catalytic converter? It can if ignored. Each misfire sends unburned fuel into the exhaust, where it burns inside the converter and overheats it. A flashing check engine light is the warning that damage is likely. Fixing the misfire quickly is much cheaper than replacing a converter on a V8. ### Can a vacuum leak cause P0307? Yes, a leak close to cylinder 7, such as a cracked intake gasket near its port, can lean out just that cylinder. The misfire is usually worst at idle. A smoke test is the quickest way to find it. A leak elsewhere usually affects several cylinders and sets lean codes too. ### Will P0307 pass inspection? No, a car with P0307 and the check engine light on fails an OBD-based emissions inspection in most states. After the repair, clear the code and drive normally for several days so all readiness monitors complete. Confirm they show ready on a scan tool before going back for a retest. ### Why does P0307 come back after a new spark plug? It usually returns because the plug was not the only problem. A weak coil, a plug wire arcing to the exhaust, a leaking injector or a mechanical fault such as a collapsed lifter can all keep cylinder 7 misfiring. Swap tests and a compression check narrow down the remaining cause. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other ignition and misfire codes - [P0300 Random/Multiple Cylinder Misfire Detected](https://diagxcar.com/codes/p0300) - [P0301 Cylinder 1 Misfire Detected](https://diagxcar.com/codes/p0301) - [P0302 Cylinder 2 Misfire Detected](https://diagxcar.com/codes/p0302) - [P0303 Cylinder 3 Misfire Detected](https://diagxcar.com/codes/p0303) - [P0304 Cylinder 4 Misfire Detected](https://diagxcar.com/codes/p0304) - [P0305 Cylinder 5 Misfire Detected](https://diagxcar.com/codes/p0305) - [P0306 Cylinder 6 Misfire Detected](https://diagxcar.com/codes/p0306) - [P0308 Cylinder 8 Misfire Detected](https://diagxcar.com/codes/p0308) - [P0316 Engine Misfire Detected on Startup (First 1000 Revolutions)](https://diagxcar.com/codes/p0316) - [P0320 Ignition/Distributor Engine Speed Input Circuit](https://diagxcar.com/codes/p0320) ## Symptoms - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car shake at idle?](https://diagxcar.com/symptoms/car-shakes-at-idle) - [Why does my car shake when I accelerate?](https://diagxcar.com/symptoms/car-shakes-when-accelerating) - [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating) ## Repair costs - [Spark plug replacement cost](https://diagxcar.com/cost/spark-plug-replacement): $120-$450 - [Ignition coil replacement cost](https://diagxcar.com/cost/ignition-coil-replacement): $150-$400 - [Fuel injector replacement cost](https://diagxcar.com/cost/fuel-injector-replacement): $300-$1,500 --- Source page: https://diagxcar.com/codes/p0307 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.