ME-SFI Lambda Control Function

ME-SFI Lambda Control Function




Shown on Engine 119
158 Three-way catalytic converter
B2/5 Hot film mass air flow sensor
B11/4 Coolant temperature sensor
B37 Accelerator pedal sensor
G3/3 Left O2 sensor upstream of TWC
G3/4 Right O2 sensor, upstream of TWC
N3/10 ME-SFI control unit
Y62 Injectors (LH-SFI, HFM-SFI, PEC [LH, HFM, PMS])

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

The O2 sensor reacts to the oxygen concentration in the exhaust and transmits the corresponding voltage signal to the ME-SFI control unit for fuel injection, which thereupon alters the mixture composition in such a way as to produce a mixture composition of lambda = 1 in all operating states when the lambda closed-loop control is active. This procedure is constantly repeated (control loop), the frequency is dependent on engine load and speed. The ME-SFI control unit alters the mixture composition with a time delay in order to prevent any risk of jerking. The lambda closed-loop control is operational in the following conditions (closed-loop control):
- Coolant temperature > 52° C
- O2 sensors have reached operating temperature
- Idle speed/part load
- Deceleration fuel shutoff not active.





Note: (USA) Engine 112.946 with code 929 Flexible Fuel Vehicle (FFV)
After each fueling the Ethanel portion is determined by means of the O2sensor voltage upstream TWC in the fuel tank. If for example Ethanol was refueled, the mixture is at first too lean (oxygen sensor voltage jumps back to 0 Volt). The lambda control reacts if the mixture to be enriched until after fueling lambda = 1 is achieved again.