Catalyst Damaging Misfiring

Misfiring may indicate that the fuel/air mixture that should have combusted in the engine has combusted in the catalytic converter instead.

hhhhh proportion of misfires causing overheating that can damage the catalytic converter depends on engine load and engine speed.

The number of misfires per 200 engine revolutions required to damage the catalytic converter is stored in the control module memory in a matrix that is dependent on load and engine speed.

When the conditions for the diagnosis have been fulfilled, the combustion signals from the ignition discharge module are assessed. If the number of misfires per 200 engine revolutions exceeds the value in the matrix, the fault criteria will have been fulfilled.

Conditions for diagnosis
- Engine running
- Ignition synchronized
- No fuel shut-off







1 Max. number of permissible misfires during 200 engine revolutions
2 Number of detected misfires ≥ max. number of permissible misfires during 200 engine revolutions
3 Combustion signals from ignition discharge module during 200 engine revolutions
4 Fault criteria for catalyst damaging misfiring fulfilled