Self-adjustment of mixture formation, function

P07.51-0405-06

d Controlled range of lambda control factor

e Control factor prior to self-adaptation (lean)

g Control factor following self-adaptation

h Position of lambda performance map prior to self-adaptation

On vehicles with controlled catalytic converter the lambda control determines the injection time to such a degree of exactness that the fuel-air ratio λ=1 under all operating conditions.

If faults occur, the ME-SFI [ME] control unit automatically makes a correction in the mixture formation. Here the lambda performance map is shifted within certain limits in such a way that the lambda control is not at the upper or lower regulation limit (d).

The following faults require a mixture adjustment:

 Unmetered air

 Wear or carbon deposits on fuel injection valves

 Transition resistance in the air flow meter

 Incorrect injection pressure (e.g. through plugged fuel filter or harmful diaphragm pressure regulator)

 Faulty purge control valve with high enrichment from activated charcoal canister

 Engine wear (e.g. leaky valves)

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If the mixture composition constantly drifts out of the middle control range (e.g. 0  10%) the ME-SFI [ME] control unit under certain operating conditions shifts the lambda map 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).

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This self-adjustment of the mixture formation can be carried out in the following operating states:

 Idle speed

 Lower part load

 Upper partial load.

The following actual values can be read out using STAR DIAGNOSIS:

 Lambda map shift active

 Direction of the shift (tendency towards rich or lean)

 Extent of the shift

Presentation of the self- adjustment values using HHT or

STAR DIAGNOSIS in idle

The representation in ms means that the value displayed is added to, or subtracted from, the air mass inducted by the engine in order to determine the injection time.

The maximum correction value is 1 ms.

Example:

Calculated injection time (performance map): 3.0 ms

Displayed correction value: +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).

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Presentation of the self- adjustment values using HHT or

STAR DIAGNOSIS for lower and upper partial load

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

The correction factor lies between 0.68 and 1.32.

Example:

Measures air mass throughput: 150 kg/hour

Displayed correction value: 1.10

A calculated air mass value of the of 165 kg/h is used by the engine control unit to determine the injection time (fuel injection quantity).

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 Flexible Fuel Vehicle (FFV) for engine 112 with code 929

The ethanol factor has a multiplying effect on the fuel injection amount of 1.0 to 1.43 and leads to extended self-adjustment of the mixture formation.

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