Self-adjustment of mixture formation, function - GF07.10-P-1029M

ENGINE 275.950 in MODEL 215, 220

ENGINE 275.951 in MODEL 230 up to model year 2008 /AEJ 07

ENGINE 275.953 in MODEL 216, 221 up to model year 2008 /AEJ 07

ENGINE 275.954 in MODEL 230 up to model year 2008 /AEJ 07

ENGINE 275.980 in MODEL 215, 220

ENGINE 275.981 in MODEL 230 up to model year 2008 /AEJ 07

ENGINE 275.982 in MODEL 216, 221 up to model year 2008 /AEJ 07

ENGINE 285.950 in MODEL 240

ENGINE 285.980 in MODEL 240

Fig 1: Identifying Shifting Of Lambda Performance Map

Courtesy of MERCEDES-BENZ USA

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 (X) 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)
Incorrect load sensing
Wrong injection pressure (e.g. defective fuel pressure sensor (B4/7))
Defective purge control valve (Y58/1)
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 partial load (suction operation)
Upper partial load (load operation).

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

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).

The maximum correction value is ±1.0 ms.

Representation of self-adaptation values using the DAS for partial load

The representation of the factor means that the indicated value for determining the injection time is multiplied by the air mass inducted by the engine.

Representation of self-adaptation values using the DAS in idle

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

Indicated value with the DAS: +0.3 (ms)

Example:

Calculated air mass: 150 kg/hour

Indicated value with the DAS: 1.10

A computed value of the air mass of 165 kg/h is used by the ME-SFI [ME] control unit to determine the injection time (fuel quantity injected).

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

ME-SFI [ME] control unit, location/task/ design/function	GF07.61-P-5000M
O₂ sensors, location/task/design/function	GF07.04-P-4103M