Powertrain, generic · Ignition system or misfire

P0307 Cylinder 7 Misfire Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

The engine module detects misfire from crankshaft speed: a cylinder that does not fire gives no acceleration impulse. At a catalyst-damaging rate (CARB: at least 5 % per 200 revolutions) the warning light flashes; at an emissions-relevant rate (at least 1 % per 1,000 revolutions – GM about 2–5 %, Ford 0.9–1.5 %) it comes on after two trips. Ford and GM may shut off a misfiring cylinder's injector to protect the catalyst. P0307 means more than 90 % of the detected misfires fall on cylinder 7. Usual causes are the ignition coil or spark plug of that cylinder, its injector, or low compression; a quick test is to swap coil or plug with a neighbouring cylinder and see whether the misfire moves. On V8 engines GM bulletins name loose coil connectors and a loose coil ground on the cylinder head.

Likely causes

Ignition coil of cylinder 7 faulty (coil, connector, ground)
Spark plug of cylinder 7 worn, sooted, cracked or wrongly gapped
Injector of cylinder 7 clogged or leaking, or its control
Low compression on cylinder 7 (valve, rings, head gasket) or local false air
Water or oil in the plug well

Symptoms

  • Check engine light on, flashing at a catalyst-damaging rate
  • Rough idle, jerking, vibration
  • Loss of power, hesitation
  • Smell of unburnt fuel, higher consumption

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–800
Time0.3–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

ignition coil cylinder 7spark plug cylinder 7fuel injector cylinder 7

Related codes

P0300P0357P0207P0316P0420

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.