On-Board Diagnosis System II - Volkswagen Technical Site

System Components (Gasoline Engine)
The misfire detection system
1
Cylinder-selective misfire detection:
2
Example: Cylinder 4 misfires
B
1 2
A Crankshaft signal:
possible misfiring on cylinder 1 or 4
3
B Camshaft signal:
Recognition of position of cylinder 1
Signal A+B
= misfiring on cylinder 4
A 3 4
Legend:
1 Motronic control unit
2 Hall sender
3 Engine speed sender
175_095
If a misfire occurs, the air-fuel mixture is discharged
unburnt to the exhaust gas stream.
In addition to loss of engine power and a
deterioration in exhaust emission quality, the
main hazard involves overheating or damage to
the catalytic converter due to the increased
catalytic combustion rate.
Road surface unevenness may be misinterpreted
as misfiring. Therefore, the misfire detection
system is switched off by the engine management
system when severe road unevenness
occurs.
The basic principle of the misfire detection system
is based on cylinder-selective detection of
irregular engine running.
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