Toyota vehicles have a strange Total FT PID. At first glance, one would expect the normal definition of Total FT = Short FT + Long FT. However, the data shows that this is not the case. I was not able to find a clear definition of what Total FT is, but this post tries to explain it a bit more than 'average total fuel trim - page 260)'. If the actual method of calculation of Total FT is in the public domain somewhere, please let me know.
Here is an example. The graph below shows the Short FT, Long FT and Total FT on bank #2 for a vehicle with obvious issues.
A couple of notes about the Techstream graphs:
(1) The y-scaling is a bit confusing. There are 3 numbers. The top and bottom numbers (0.011 and 0.460 for the lower graph) are the min and max of the graph. The middle number (0.300) is the value of the PID at the current cursor location (it is not a scale value).
(2) To add a graph, click and drag the data PID from the Parameter column on the left onto the graph area. It will be added as a new graph. (Alternatively, the PID parameter can be double-clicked.)
(3) The "Overlap" button will show all PIDs in a single graph.
(4) Zoom in on the data by dragging a rectangular section that will be zoomed in. Double click to un-zoom.
Back to Total FT:
The ECM divides the operating regime of the engine into cells. For each cell a different value of the learned LFT is stored. When changing load, the LFT from the relevant cell will be retrieved and used at that moment. This explains the 'stepwise' behaviour of the LFT (middle graph). If the rpm/load is held constant and there is a non-zero SFT, the LFT will be gradually updated. See for example the last bit of data of the graph where the LFT is slowly learning towards more negative trim. As a result of this updating of the LFT, the SFT gets closer to zero.
If TFT was simply the addition of LFT and SFT, it would also show this staircase behavior. Looking at the last graph of Total FT, it is a very smooth parameter. Based on the limited information online, it seems that Total FT is some form of running average of the LFT and SFT and is therefore much more smooth then the sum of LFT+SFT. It is also not expressed as a percentage, but as a decimal (e.g. 30% total trim = 0.30).
Here is an example. The graph below shows the Short FT, Long FT and Total FT on bank #2 for a vehicle with obvious issues.
A couple of notes about the Techstream graphs:
(1) The y-scaling is a bit confusing. There are 3 numbers. The top and bottom numbers (0.011 and 0.460 for the lower graph) are the min and max of the graph. The middle number (0.300) is the value of the PID at the current cursor location (it is not a scale value).
(2) To add a graph, click and drag the data PID from the Parameter column on the left onto the graph area. It will be added as a new graph. (Alternatively, the PID parameter can be double-clicked.)
(3) The "Overlap" button will show all PIDs in a single graph.
(4) Zoom in on the data by dragging a rectangular section that will be zoomed in. Double click to un-zoom.
Back to Total FT:
The ECM divides the operating regime of the engine into cells. For each cell a different value of the learned LFT is stored. When changing load, the LFT from the relevant cell will be retrieved and used at that moment. This explains the 'stepwise' behaviour of the LFT (middle graph). If the rpm/load is held constant and there is a non-zero SFT, the LFT will be gradually updated. See for example the last bit of data of the graph where the LFT is slowly learning towards more negative trim. As a result of this updating of the LFT, the SFT gets closer to zero.
If TFT was simply the addition of LFT and SFT, it would also show this staircase behavior. Looking at the last graph of Total FT, it is a very smooth parameter. Based on the limited information online, it seems that Total FT is some form of running average of the LFT and SFT and is therefore much more smooth then the sum of LFT+SFT. It is also not expressed as a percentage, but as a decimal (e.g. 30% total trim = 0.30).
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