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

GF07.61-P-4019MIS ME-SFI Overrun Fuel Shutoff, Function
- 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 mode (if Distronic PLUS installed)
^ 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), engine speed
- Electric controller unit (VGS) (Y3/8), shift stage over the drive train CAN (CAN C)

Function sequence for deceleration fuel shutoff
In deceleration mode, the ME-SFI [ME] control unit shuts off the fuel injection valves (Y62) according to coolant temperature, engaged gear and engine speed, if the accelerator pedal is not actuated. The fuel injection valves are switched on again when the accelerator pedal is operated.

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

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

In order to prevent a sudden rise in torque when combustion is restarted after a deceleration fuel shutoff, the ME-SFI [ME] control unit briefly shifts the ignition angles 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 of the catalytic converters.