Note: Refer HERE for a detailed explanation of Overrun Fuel Cut settings.
Overrun Fuel Cut
When the throttle is abruptly closed the engine generates more vacuum than under normal conditions (such as idle and light cruising), this condition is known as overrun. During overrun the ECU performs a fuel cut by switching off all injectors, this helps minimise the possibility of backfiring and reduces fuel consumption and emissions.
The overrun fuel cut activates if both the throttle (or accelerator) position is less than the TP/AP Threshold AND the engine speed is greater than the current value in the Overrun Deactivation Table.
Setup Notes
·The overrun condition is recognised when the throttle is closed and the engine speed is above the set value, as a result this function can only be used if a throttle position sensor (TPS) is fitted and correctly setup.
·If Electronic Throttle Control is used, Overrun Fuel Cut will use the Accelerator Position Sensor (APS) value (instead of the TPS) value, i.e. overrun fuel cut will become active below the APS value specified in the TPS/APS Threshold value. If Cruise Control is used the Overrun Fuel Cut will use a combination of APS and TPS.
·When using Electronic Throttle Control it is important that a very low angle of throttle is present when the fuel re-activates to stop a surge forward as the fuel comes back in.
Note: Overrun Fuel cut will not activate if Antilag is active
Note: Overrun Fuel cut will be temporarily deactivated when Gear Shift Control performs an Overrun Up Shift or Overrun Down Shift.
Overrun Fuel Cut Example
This example helps to explain how the different settings of Overrun Fuel Cut work.
The following Overrun Fuel Cut settings are used:
TP/AP Threshold: 5.0 %
Activation Delay: 0.5 s
Torque Reduction/Introduction Time: 2.00 s
Ignition Retard: -10.0 °
Current value from the Overrun De-Activation RPM Table: 1600 RPM
The image below shows the different stages of the Overrun Fuel Cut function working:
The following steps happen in order:
1.The engine speed is above the current value from the Overrun De-Activation RPM Table (1600 RPM).
2.The throttle position (TP(Main))decreases to below the TP/AP Threshold (5.0%).
3.The activation delay occurs (0.5s).
4.The Ignition Retard (-10.0°) is introduced over the period specified for Torque Reduction/Introduction Time (2.00s).
5.The Over-run Fuel Cut commences and continues until the engine speed falls below the current value from the Overrun De-Activation RPM Table (1600 RPM).
6.The Ignition Retard is reduced to zero over the period specified for Torque Reduction/Introduction Time (2.00s).