GF07.61-P-4019V ME-SFI Deceleration Fuel Shutoff, Function

GF07.61-P-4019V ME-SFI Deceleration Fuel Shutoff, Function







Deceleration fuel shutoff has the following tasks:
- Increasing the braking power of the engine in the deceleration mode
- Reducing fuel consumption
- Improving exhaust emissions in the deceleration mode.

In the overrun mode, the ME control unit switches off the fuel injection valves depending on the coolant temperature and the gear engaged, if the accelerator pedal is not operated (detected via the actual value signal from the accelerator pedal sensor). The fuel injection valves are switched on again when the accelerator pedal is operated.

The deceleration fuel shutoff is suppressed at too high exhaust gas temperatures, because the high oxygen content in the exhaust during deceleration fuel shutoff can lead to an increased oxidation of carbon monoxide and hydrocarbon (afterburning). This can result in additional heat (thermal reaction) that can overheat the catalytic converters.

After the deceleration mode, the mixture is briefly enriched in order to eliminate the enriched oxygen in the three way catalytic converters resulting from the deceleration mode. The valve overlap is also set to its minimum value by the camshaft adjustment. This ensures that an optimal 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".

The engine speed when combustion cuts in is dependent on the coolant temperature, the engine and transmission versions and with automatic transmission, dependent on the drive position selected (via the CAN from the transmission control unit).

Deceleration fuel shutoff is blocked under the following conditions:
- with automatic transmission in selector lever position P or N
- with manual transmission with clutch pedal depressed.