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

ENGINE 275.953 in MODEL 216.376, 221.176 as of Model Year 09/AEJ 08

ENGINE 275.982 in MODEL 216.379, 221.179 as of Model Year 09/AEJ 08

Exhaust gas conversion in the three way catalytic converter

Fig 1: Three Way Catalytic Converter Exhaust Gas Conversion Characteristic Graph

Courtesy of MERCEDES-BENZ USA

Function requirements for lambda regulation, general points

Circuit 87M ON (engine control ON)
Engine running
Coolant temperature >52°C
Operating temperature reached in LH and RH O ₂ sensors upstream of CAT (G3/3, G3/4)
Engine idling or partial-load range
Deceleration fuel shutoff not active.

Lambda regulation, general points

The mixture composition is controlled within the narrowest limits around λ = 1 in order to achieve high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters. For this purpose, the ME-SFI control unit (N3/10) reads the following sensors:

Coolant temperature sensor (B11/4)
Charge air temperature sensor (B17/8) and pressure sensor downstream of throttle valve actuator (B28/7), engine load
LH and RH O₂ sensors upstream of CAT, oxygen sensor signals

Lambda regulation function sequence

The O ₂ sensors upstream of the CAT react to the oxygen content in the exhaust and send the corresponding voltage signals to the ME-SFI control unit. This then regulates the mixture composition by adjusting the injection time of the fuel injection valves (Y62) so that λ=1 is reached. This process is repeated constantly (control loop).

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

Fig 2: Lambda Regulation Block Diagram

Courtesy of MERCEDES-BENZ USA

Example:

Assuming a leaner fuel-air mixture is produced. This has the consequences that the oxygen sensor voltage drops and the ME-SFI control unit compensates for the leaner mixture by enriching it accordingly (extending the injection time).

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

The lambda control factor indicated with the Diagnosis Assistance System (DAS) changes 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 3: Display Lambda Regulation Factor

Courtesy of MERCEDES-BENZ USA

ME-SFI [ME] control unit, component description

N3/10

GF07.61-P-6000MOS