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

ENGINE 113.967 in MODEL 219 

ENGINE 113.964 in MODEL 164.1 

ENGINE 113.971 in MODEL 251 

Shows model 219 

Fig 1: ME-SFI Lambda Control Communication Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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 upstream of the TWC the oxygen concentration in the exhaust and transmit corresponding signals to the ME control unit. This alters the mixture composition in such a way that the desired lambda (usually λ=1) is set so in all operating conditions of the engine.

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: Catalytic Converter Coolant Temperature Graph

  Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
  Fig 3: Air/Fuel Mixture Flow Chart

  Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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 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 control unit.

Fig 4: Air/Fuel Mixture Chart

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.