Computers and Control Systems: Adjustments

GF07.10-P-1029AMG Self-adjustment Of Mixture Formation, Function







On vehicles fitted with a closed-loop controlled catalytic converter the lambda control determines the injection time so exactly that a certain fuel-air ratio (Lambda) is maintained in all operating states. The ME-SFI [ME] control unit (N3/10) automatically corrects the mixture formation if one of the following faults occurs:
- Unmetered air
- Wear or carbon deposits on fuel injection valves (Y62)
- Defective pressure sensor (B28)
- Transition resistance in left or right hot film mass air flow sensor (B2/6, B2/7)
- Defective purge control valve (Y58/1)
- Harmful fuel pressure regulator
- Defective fuel pressure sensor (B4/15)
- Wear to the engine (e.g. valve leakage)

In this case, the lambda map is shifted within certain limits so that the lambda control is not positioned at the lower or upper control stop.

If the mixture composition constantly drifts out of the middle control range (e.g. 0 ± 10%), the ME-SFI [ME] control unit shifts the lambda map under certain operating conditions sufficiently far until a lambda control factor of approx. 0% (g) is again achieved.

Self-adjustment ensures that the mixture composition in the control mode (e.g. warming-up phase) is neither too rich nor too lean. This also prevents the lambda control from moving up to the control limit at high altitudes.

Example:
As the result of a lean fuel/air mixture the readout of the lambda control factor changes to 18 % (e). Under certain operating conditions the lambda performance map is shifted (arrow) by the ME- SFI [ME] control unit.

This shifting of the lambda performance map is the self-adjustment of the mixture formation process to the existing air/fuel mixture. After this self-adjustment the lambda control factor is again in the central control range (g).

Self-adjustment of the mixture formation can be carried out in the following operating states:
- Idle speed
- Lower part load
- Upper part load

The following can be read out with STAR DIAGNOSIS:
- Whether the lambda performance map has been shifted
- The direction of the shift (rich or lean)
- How far the lambda performance map has been shifted

Representation of self-adaptation values with STAR DIAGNOSIS:
The representation is performed in "ms" and means that the displayed value for determining the injection time is either added to or subtracted from the injection time determined by the performance map.

Example:
Calculated injection time (performance map): 3.0 ms
Value displayed in STAR DIAGNOSIS: +0.3 (ms)

For determining the injection time (fuel injection quantity) the ME-SFI [ME] control unit uses a calculated value of 3.3 ms (3.0 ms+0.3 ms).

Idle correction value
The maximum correction value is ± 1.0 ms.

Partial load correction value
The maximum correction value is -0.68 to +1.32 ms.