Engine Control Module (ECM) [2014-2016, B4204T11]: Function: Misfiring

If the fuel / air mix does not completely ignite in the combustion chamber, the engine misfires. 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 fuel / air mixture
  • poor ignition sparking
  • insufficient compression
• normal variations caused by uneven combustion
  • incorrect fuel / air mixture
  • poor ignition sparking
  • insufficient compression
• flywheel mechanical tolerances
  • incorrect fuel / air mixture
  • poor ignition sparking
  • insufficient compression
• misfiring, which is caused by:
  • incorrect fuel / air mixture
  • poor ignition sparking
  • insufficient compression

Diagnostics 

The mechanical tolerances and oscillations in the drive line disrupt the signal. This makes it difficult to determine if a misfire has occurred or if the detection is incorrect. In order to eliminate the mechanical variations of the flywheel, the flywheel signal is adapted to filter out the irregular rotation.

Misfires can be detected by registering the time difference between the intervals and comparing this with the filtered time difference in the flywheel. If the flywheel signal has not been adapted, the diagnostic is active. However this cannot identify misfires as accurately as an adapted flywheel signal. The adaptation is carried out at different loads and engine speed ranges. For the values to be set in the different ranges, the deviation in speed must be within certain fixed limits.

The misfire diagnostic is shut off when certain component faults have been detected by the Engine Control Module (ECM).

"Rough Road" detection (drivetrain oscillations caused by, for example, extremely uneven roads) is not activated on this engine.

Diagnostic Trouble Code (DTC) management

DTC for misfire lights the MIL light. The Engine Control Module (ECM) determines how much the engine is misfiring by counting the number of misfires during a certain number of engine revolutions.

Misfire affecting emission levels 

If Engine Control Module (ECM) detects a certain number of misfires during 1, 000 engine revolutions this is interpreted as misfiring that affects emissions. Fault code is stored and the MIL-light is turned on. Directly in connection with engine start, that is, during the engine's first 1, 000 revs after start, the misfiring diagnosis is four times as sensitive as later in the driving cycle.

Catalytic converter damaging misfire 

If the Engine Control Module (ECM) detects a certain number of misfires during 200 engine revolutions, this is interpreted as misfiring which damages the three-way catalytic converter. The number of misfires that the Engine Control Module (ECM) allows before interpreting it as misfiring depends on the load and engine speed range. the Malfunction Indicator Lamp (MIL) flashes when the misfire occurs, and shines constantly once the Diagnostic Trouble Code (DTC) is stored.

The Engine Control Module (ECM) registers and stores the engine's speed range, load range and information about the engine temperature when misfiring is detected. If misfiring stops, the same speed range, load range and engine temperature without misfiring must be met, so that the Engine Control Module (ECM) can start countdown for light extinguishing and erasing of stored DTCs for misfiring.

The number of misfires can be read off.