Ignition

P0307 — Cylinder 7 Misfire Detected

Severity: medium Drive with care, to a shop

What P0307 means

The ECM watches crankshaft speed variations and uses them to tell when cylinder 7 is not burning its air-fuel mixture properly. A cylinder needs a good spark, the right amount of fuel, enough compression and correct airflow. If any of these fails, the cylinder misfires and P0307 is stored.

Symptoms

  • Check engine light on or flashing
  • Rough idle and engine vibration
  • Hesitation or stumbling when accelerating
  • Loss of power under load
  • Worse fuel economy
  • Hard starting
  • Raw fuel smell from the exhaust

Possible causes

  1. Worn or faulty spark plug in cylinder 7
  2. Failed ignition coil on cylinder 7
  3. Clogged or faulty fuel injector on cylinder 7
  4. Vacuum leak near cylinder 7 (intake gasket, cracked hose)
  5. Low compression: valve, piston rings or head gasket
  6. Damaged wiring or connector at the coil or injector
  7. Rarely, a faulty crankshaft or camshaft position sensor

How to diagnose

  1. Read codes and freeze frame data, and look at per-cylinder misfire counters
  2. Check for other codes, especially on neighboring cylinders or random misfire
  3. Inspect the cylinder 7 spark plug for wear, fouling, oil or a cracked insulator
  4. Swap the coil (and plug) with a good cylinder, clear the code and see if the misfire follows
  5. Check the coil and injector connectors, wiring, power and control signal
  6. Test the injector: listen to it, measure resistance, compare cylinder balance
  7. Inspect the intake system for vacuum leaks (smoke test, hoses, gaskets)
  8. If ignition and fuel check out, run a compression test and a leak-down test if needed

Common fixes

  • Replace spark plugs, ideally as a full set
  • Replace the cylinder 7 ignition coil
  • Clean or replace the cylinder 7 fuel injector
  • Fix vacuum leaks by replacing the gasket or damaged hose
  • Repair damaged wiring and connectors
  • Repair internal engine problems (valves, rings, head gasket)

Questions and answers

What does P0307 mean?

It means the ECM detected a misfire in cylinder 7, so the mixture there is not burning properly. The usual culprits are the spark plug, ignition coil or fuel injector.

Can I drive with P0307?

Briefly and gently if the light is steady. If the light flashes, do not drive, because the catalytic converter and engine can be damaged quickly.

How do I tell if it's the plug or the coil?

Swap the cylinder 7 coil with one from another cylinder and clear the code. If the misfire moves, the coil is bad. If not, check the plug, injector and compression.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.