How it works

The Long Term Fuel Trim is a function where the ECU can learn the correct amount of fuel required over a period of time so that the Target and Actual measured AFR are equal. Sometimes this is referred to as Auto-Tune. Both Narrowband and Wideband O2 sensors can be used for Long Term O2 Control, however a Wideband O2 Sensor is preferred. Long Term O2 Control can allow for fine correction of the Fuel Base table in areas that may not be obtainable during the tuning process, for engine wear over time, or for self-tuning for small modifications. Mapping is available up to 4D.

Enable Long Term Fuel Trim

Enables or Disables the Long Term Fuel Trim Function. When Enabled, new tables are available in the Navigation Tree. (Default = Disabled)

LTFT Max Enrich

Sets the maximum positive (enrichment) correction that the Long Term Fuel Trim (LTFT) will allow. (Default = 15)

LTFT Max Disenrich

Sets the maximum negative (enleanment) correction that the Long Term Fuel Trim (LTFT) will allow. (Default = 15)

Long Term Fuel Trim Rich Bias

Allows the Long Term to learn an amount richer than the Target to allow for a safe tune condition should the system revert to open loop control, perhaps due to sensor failure. The short term control would then correct back to the Target Lambda from this learned bias. To disable this function it should be set to "0". (Default = 3)

Long Term Fuel Trim Min Temperature

Sets the minimum coolant temperature before the Long Term control will activate. This is to prevent the long term table form learning values from a cold engine. (Default = 60)

Disable During Post Start Corr

When enabled, the Long Term control will be disabled when the Fuel Post Start Correction table is outputting anything other than 0%. This is sometimes required when the tuner does not wish to allow the Long Term control to function whilst a start-up enrichment is active. (Default = Disabled)

Disable During Coolant Corr

When enabled, the Long Term control will be disabled when the Fuel Coolant Correction table is outputting anything other than 0%. This is sometimes required when the tuner does not wish to allow the Long Term control to function whilst the engine is not at full operating temperature. (Default = Disabled)

Reset

Resets all Long Term correction tables back to zero.

Apply to Base Table

Applies any Long Term corrections to the Fuel Base table, and after applying these changes it will reset to zero. When a second engine bank is being used, the Long Term system will apply the difference between the two banks to the Fuel Base table, and any remaining differences will remain in the table. All values that were equal will reset to zero. This must be done in this way due to there being two Long Term correction tables, and only one Fuel Base table to apply to.

Long Term Fuel Trim Gain

Tuning

Controls the rate at which the Long Term O2 Control can make corrections to the Long Term Fuel Trim tables. Larger numbers will learn faster but can cause oscillations, and smaller numbers will make corrections at a slower rate. Up to 3D mapping is available (Default = 30)

Bank (1&2) Long Term Fuel Trim

Axis selection and changing values

This table is user definable for the axis values, however the axis channels are fixed to be the same as those used for the Fuel Base table. Any axis values that are changed for this table are also changed for Bank 2 if a second bank is active. This table can be adjusted by the tuner simultaneously whilst the Long Term Control is making changes. Up to 4D mapping is available.

Tuning

The amount of fuel percentage correction that the Nexus VCU has learned for each given cell, or in other words, the amount of correction the Long Term O2 Control is making to Bank 1.