Deceleration fuel shutoff, function

Function requirements for deceleration fuel shutoff, general points

 Circuit 87M (engine control ON)

 Engine running

 Vehicle rolling

 Accelerator not operated

 Selector lever position "D" or "R"

 Vehicle is not in cruise control mode

 Not too high an exhaust temperature

Deceleration fuel shutoff, general

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

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The ME-SFI [ME] control unit (N3/10) performs a deceleration fuel shutoff dependent on the following sensors and signals:

- Coolant temperature sensor (B11/4)

- Accelerator pedal sensor (B37), accelerator pedal position

- Crankshaft Hall sensor (B70) (with direction of rotation recognition), motor rpm

- Fully integrated transmission control unit for dual clutch transmission (Y3/14n4), stage via the drive train CAN (CAN C)

Deceleration fuel shutoff, function

In decel mode the ME-SFI [ME] control unit switches the fuel injectors (Y76) or over the CNG control unit (N118/2) the gas injection valves gas (Y106) dependent on the coolant temperature, the engaged gear and the engine rpm, if the accelerator pedal is not actuated.

The fuel injectors or the gas injection valves gas are switched on again when the accelerator pedal is actuated.

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The ME-SFI [ME] control unit also adjusts the valve overlap to its minimum value through the intake camshaft solenoid (Y49/1) and the exhaust camshaft solenoid (Y49/2). This ensures that an optimal conversion rate of the catalytic converter 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 or gas blowing in time, in order to protect of the catalytic converter 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 (afterburning). The heat so generated can overheat of the catalytic converter.