GF07.61-P-4019MIR ME-SFI Overrun Fuel Shutoff, Function

GF07.61-P-4019MIR ME-SFI Overrun Fuel Shutoff, Function
- refinement package
- as of model year 09


Function requirements for deceleration fuel shutoff, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
^ Vehicle rolling
^ Accelerator not operated
^ Selector lever position "D" or "R"
^ Vehicle not in cruise control or Distronic operation (if Distronic is present)
^ Not too high an exhaust temperature

Deceleration fuel shutoff, general points
Deceleration fuel shutoff in deceleration mode of the engine has the following tasks:
- Increasing the braking effect of the engine
- Reducing fuel consumption
- Improving exhaust characteristics

The ME-SFI (N3/10) control unit performs a deceleration fuel shutoff according to the following sensors and signals:
- Coolant temperature sensor (B11/4)
- Accelerator pedal sensor (B37), accelerator pedal position
- Crankshaft Hall sensor (B70), motor speed
- Electric controller unit (VGS) (Y3/8), gear stage over the engine compartment CAN (CAN C)

Deceleration fuel shutoff function sequence
In deceleration mode, the ME-SFI control unit switches off the fuel injection valves (Y62) depending on coolant temperature, selected gear and engine speed, and if the accelerator pedal is not actuated. The fuel injection valves are switched on again when the accelerator pedal is operated.

Through the LH and RH intake camshaft solenoids (Y49/4, Y49/5) and LH and RH exhaust camshaft solenoids (Y49/6, Y49/7), the ME- SFI control unit also adjusts the valve overlap to minimum value. This ensures that an optimal conversion rate of the catalytic converters is more rapidly achieved.

After deceleration fuel shutoff, the ME-SFI control unit enriches the fuel-air mixture by briefly extending the injection time, in order to protect the catalytic converters from enriched oxygen.

In order to prevent a sudden rise in torque when the combustion is restarted after a deceleration fuel shutoff, the ME-SFI control unit briefly shifts the firing points of the ignition coils (T1) towards "retard".

Deceleration fuel shutoff is disabled when exhaust temperatures are too high, since the high oxygen content occurring in the exhaust during a deceleration fuel shutoff could cause increased oxidation of carbon monoxide and hydrocarbon (after burning). The heat so generated can overheat the catalytic converters.