ME-SFI lambda control, function - GF07.61-P-4022KE

ENGINE 271.921 in MODEL 203

ENGINE 271.940 in MODEL 203, 209

ENGINE 271.941 in MODEL 211

ENGINE 271.944 in MODEL 171

ENGINE 271.946 in MODEL 203

ENGINE 271.948 in MODEL 203

ENGINE 271.955 in MODEL 209

ENGINE 271.956 in MODEL 211

Fig 1: ME-SFI Lambda Control, Function (Engine 271)

The mixture composition is controlled within the narrowest possible limits around λ = 1 in order to achieve a high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters.

The O₂ sensor upstream of TWC reacts to the oxygen share in the exhaust and transmits a corresponding voltage signal to the ME control unit. Consequently, the mixture composition is modified by control of the injection quantity, so that λ=1 is obtained. This process is repeated constantly (control loop).

The ME control unit alters the mixture composition with a time delay in order to prevent any risk of jerking.

Control of the air/fuel ratio is much faster by using a wideband oxygen sensor (continuous signal of λ 0.7 to 4.0) as an O₂ sensor upstream of TWC.

The function of the lambda control (closed-loop operation) is dependent upon:

Coolant temperature at start (dependent on the particular operating condition)
Operating temperature of the O₂ sensor upstream of TWC
Engine idling or partial-load range
Deceleration fuel shutoff not active.

Exhaust gas conversion in the three way catalytic converter

Fig 2: Exhaust Gas Conversion Graph

Fig 3: Lambda Control Loop Flow Diagram

Example:

Assuming a leaner fuel-air mixture is produced. This has the following consequence, that the O₂ sensor voltage drops and the ME control unit compensates for this lean drift through a matching enrichment.

This makes it possible to achieve a fuel-air mixture of approximately λ = 1.

The reading of the lambda control factor with the STAR DIAGNOSIS moves towards +25 % The more the lambda control factor moves in the direction +25%, the leaner is the fuel-air mixture and the greater is the enrichment of the mixture on the part of the ME control unit.

Fig 4: Lambda Control Factor (Display With STAR Diagnosis)

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Component description for the crankshaft position sensor	L5	GF07.04-P-6010KE
Component description for the coolant temperature sensor	B11/4	GF07.04-P-6040KE
Component description for O₂ sensors	G3/1, G3/2	GF07.04-P-6100KE
Component description for the hot film mass air flow sensor	B2/5	GF07.07-P-6000KE
Component description for the ME-SFI [ME] control unit	N3/10	GF07.61-P-6000KE
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Component description for the three-way catalytic converter	157, 158	GF49.10-P-2010KE