ME-SFI lambda control, function engine 272 - GF07.61-P-4022V

ENGINE 272.942 in MODEL 171 

ENGINE 272.963 in MODEL 171 

Shown on engine 272 

Fig 1: ME-SFI Lambda Control, Function (Shown On Engine 272)

Courtesy of MERCEDES-BENZ USA

The mixture composition is maintained within limits as close as possible to λ=1 in order to achieve a high conversion of the exhaust gases in the catalytic converter.

The O₂ sensors detect the oxygen share in the exhaust and transmit corresponding signals to the ME-SFI [ME] control unit. This changes the mixture composition so that in all engine operating statuses, the desired oxygen (usually λ=1) is set.

This procedure is repeated (control loop), the control speed is dependent on engine load and speed.

The lambda closed-loop control is operational in the following operating conditions (closed-loop control):

• Coolant temperature < approx. -10°C,
• Blocking time after starting expired
• O₂ sensors upstream TWC have reached operating temperature
  Fig 2: Exhaust Gas Conversion Graph

  Courtesy of MERCEDES-BENZ USA
  Fig 3: Lambda Control Loop Flow Diagram

  Courtesy of MERCEDES-BENZ USA

Lambda control loop 

Assuming a leaner air/fuel mixture is produced. The consequence of this is that the O₂ sensor voltage drops and the ME-SFI [ME] control unit compensates for this lean drift by enriching the mixture accordingly.

This makes it possible to achieve an air/fuel composition 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 towards +25 %, the leaner is the air/fuel mixture and the greater is the enrichment of the mixture on the part of the ME-SFI [ME] control unit.

Fig 4: Lambda Control Factor (STAR Diagnosis)

Courtesy of MERCEDES-BENZ USA