Hi All,

A few people have been asking me just how the PCM decides what value to use from each table and how does it know what cell to use.

The image below shows a VE map with the kPa cells 50 to 55 and RPM cells 800 and 1200 being highlighted.
So looking at the values from the scan tool you can see how the PCM 'averages' the values from all 4 highlighted cells.
The scan snapshot on the far left shows -
MAP = 53kPa (right between the 50 and 55kPa cells)
RPM = 1030RPM (again, right between 800 and 1200RPM)
The VE value the PCM has calculated for that sample was 1.2965.
This lies 'somewhere' within that range of 4 highlighted cells in the VE map (1.1961, 1.2131, 1.2172 & 1.4357).
Looking at the other two scan samples you can see as the RPM is increasing the VE value calculated from the 4 VE cells is heading towards the value in the cell at 55kPa and 1200RPM.
So, bascially, the way the PCM interpolates the values between cells means big gaps between cells is not a major issue, it is also why some maps get away with gaps of say 5kPa or 10kPa or more, you end up getting an average value anyway, not one or the other.

Cheers,
Ross