Closed Loop Lambda

As the KV series ECU’s have two (2) Bosch LSU lambda controllers on board it is now very straight forward to have a wide band lambda system fitted simply by wiring a Bosch 4.9 LSU sensor directly to the ECU A Connector.

The Lambda Control system has a typical Short Term Fuel Trim (STFT) system as displayed in the below example log but it also has a comprehensibve Long Term Fuel Trim (LTFT) system. Whereas the STFT performs instantaneous adjustments to correct the tune the LTFT learns values based on the STFT over time and feeds forward trim values the ECU will apply. This is essentially mewans the ECU can learn what the fueling requirements are over time based on the corrections required to yield the Lambda value.

Whilst some systems can perform LTFT they generally create issues due to only having a sinlge trim percentage which is stored by the ECU. The problem with such systems is that areas of the map may be adversely affected by the LTFT. In this case the STFT has to correct further than may have been required in the first place.

In a similiar way to how some OEM factory engine management systems work, Emtron KV series ECU’s have a range table for the LTFT. There are 10 ranges which can be set by the user. The below diagram shows an example of how this may be implimented. A value of “0” disables the LTFT for that range. Each number defines a range. When in this range the LTFT looks at the STFT and loads values for these ranges. ECU settings will include rate, gains and lockouts to govern the behaviour of the LTFT system. Whenever the range is entered this value is fed forward. This in turn takes the load off the instantenous corrections the STFT otherwise would have made as the ECU is learning the trim values required for these ranges.