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

ENGINE 156.984 in MODEL 216.377, 221.077 /177 as of Model Year 09 /AEJ 08

Exhaust gas conversion in the three way catalytic converter

Fig 1: Identifying Exhaust Gas Conversion Controlled Range

Courtesy of MERCEDES-BENZ USA

Function requirements for lambda regulation, general points

Circuit 87M ON (engine control ON)
Engine running
Coolant temperature at start (dependent on the particular operating condition)
Operating temperature reached in LH and RH O ₂ sensors upstream of CAT (G3/3, G3/4)
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:

LH and RH hot film MAF sensor (B2/6, B2/7), engine load
Coolant temperature sensor (B11/4)
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).

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 O ₂ sensors upstream of CAT.

Fig 2: Identifying Lambda Regelkreis Flow 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: Identifying Lambda Control Factor Variation Chart

Courtesy of MERCEDES-BENZ USA

Electrical function schematic, lambda regulation ME	Model 216	PE07.61-P-2774-97CAC
Electrical function schematic, lambda regulation ME	Model 221	PE07.61-P-2774-97SAC
ME-SFI [ME] control unit, component description	N3/10	GF07.61-P-6000MAS