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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
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.
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.
| Electrical function schematic, lambda regulation ME | Model 216 | PE07.61-P-2774-97CAC | |
| Model 221 | PE07.61-P-2774-97SAC | ||
| ME-SFI [ME] control unit, component description | N3/10 | GF07.61-P-6000MAS |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.