Misfire Diagnostic: Misfiring

If the fuel/air mixture does not ignite completely in the ignition stroke the engine is misfiring. The engine control module (ECM) detects the misfire by registering deviations in the rotation of the flywheel.

Deviation in flywheel rotation is due to: 

• driveline oscillations
  • incorrect air/fuel ratios
  • poor ignition sparking
  • insufficient compression.
• normal variations caused by uneven combustion
  • incorrect air/fuel ratios
  • poor ignition sparking
  • insufficient compression.
• flywheel mechanical tolerances
  • incorrect air/fuel ratios
  • poor ignition sparking
  • insufficient compression.
• misfiring, which is caused by:
  • incorrect air/fuel ratios
  • poor ignition sparking
  • insufficient compression.