GF07.10-P-1029G Self-Adjustment of Mixture Formation, Function
GF07.10-P-1029G Self-adjustment Of Mixture Formation, Function
- ENGINE 273 in MODEL 463.202 /222 /236 /237 as of model year 2009 / AEJ 08
Function requirements Self-adjustment for mixture formation, general points
Circuit 87M ON (engine control ON)
Engine running
Lambda regulation active
Engine at idle or on partial load
Self-adjustment for mixture formation, general points
For regulated catalytic converters the lambda control determines the injection time so exactly that a specified fuel-air ratio (Lambda) is maintained under all operating conditions.
Self-adjustment for mixture formation, function sequence
Self-adjustment ensures that the mixture composition in the control mode (e.g. warming-up phase) is neither too rich nor too lean. It also prevents the lambda control from coming to the end stop at high altitudes.
The following errors can occur during mixture formation:
- Unmetered air
- Wear or carbon deposits on fuel injection valves (Y62)
- Faulty pressure sensor (B28) (intake manifold air pressure)
- Transition resistance in the hot film mass air flow sensor (B2/5)
- Defective purge control valve (Y58/1)
- Harmful fuel pressure regulator
- Wear on the engine (e.g. valve leakage)
If a fault occurs, the ME-SFI [ME] control unit (N3/10) automatically makes a correction in the mixture formation. In this case, the lambda performance map is shifted within the specified limits so that the lambda control is not at the upper or lower end stop.
Shifting of the lambda performance map
a Controlled range of lambda control factor
b Control factor prior to self-adaptation (lean)
c Shifting of the lambda performance map
d Control factor following self-adaptation
e Position of lambda performance map prior to self-adjustment
If the mixture composition is constantly drifting out of the middle controlled range (e.g. 0±18%), the ME-SFI [ME] control unit in certain operating conditions shifts the lambda performance map until the lambda control factor is about 0 %.
This shifting of the lambda performance map is the self-adjustment of the mixture formation process to the existing air/fuel mixture.
Once this self-adaptation has taken place the lambda regulating factor will again find itself in the medium range.
Self- adjustment values shown with the Diagnosis Assistance System (DAS)
The following information can be read out using DAS:
- Shifting of the lambda performance map
- Direction of shift (rich or lean)
- Size of the shift
Presentation takes place in the form of a factor and means that the measured air mass value is multiplied by the factor.
Example:
Measured air mass: 150.0 kg/hour
Indicated factor in the DAS: 1.1
To determine the injection duration (fuel injection quantity), the ME-SFI [ME] control unit uses a mathematical air mass value of 165 kg/h (150 kg/h X 1.1).
The maximum correction value is -0.68 to +1.32 ms.
