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

GF07.61-P-4019CY ME-SFI Overrun Fuel Shutoff, Function
- up to model year 08

Overrun fuel shutoff has the following tasks in overrun mode:
^ Increases the braking effect of the engine
^ Reducing fuel consumption
^ Improves exhaust characteristics

In overrun mode the ME-SFI [ME] control unit (N3/10) switches the injectors (Y62) off dependent on coolant temperature, gear and rpm if the accelerator pedal is not actuated.
The injection valves are switched on again when the accelerator pedal is operated.

After overrun fuel shutoff the fuel air mixture is enriched shortly to free up catalytic converters from enriched oxygen.
Adjustment of camshafts also leads to adjustment of the valve overlap to its minimum value. This ensures that an optimal catalytic converter conversion rate is more rapidly achieved.

In order to prevent a sudden torque rise when combustion is reestablished after deceleration fuel shutoff, the ignition timing is briefly adjusted towards "retarded". When combustion is reestablished, the engine speed is dependent on the coolant temperature, the engine and transmission versions and the drive position engaged (with automatic transmission 722.9).

Deceleration fuel shutoff is blocked under the following conditions:
^ Selector lever position "P" or "N" (with automatic transmission 722.9)
^ Actuated clutch pedal (with manual transmission 716.6)
^ Excessively high exhaust gas temperatures

Deceleration fuel shutoff is suppressed at excessively high exhaust gas temperatures, because the high oxygen content in the exhaust during deceleration fuel shutoff can lead to increased oxidation (after burning) of carbon monoxide and hydrocarbon. The heat so generated can overheat the catalytic converters.