How does the PCM determine % of Ethanol?

[n8dogg]

This may be a really dumb question, but I am not too familiar with E40/E38 PCMs. So, how does the PCM determine the percentage of Ethanol in the fuel? AFAIK the narrowbands are normal and there are not any special fuel sensors in the tank. So what input is the PCM looking at to determine this? Is the normal and PE AFR adjusted accordingly? Thanks.

[joecar]

Hey n8,

if your OS is not flex fuel, then it doesn't.

if your OS is flex fuel and there is no physical sensor, then it looks at how the LTFT's change you add gas to the tank (very simplistic description).

[joecar]

If the OS is flex fuel, then it has an Ethanol open loop fuel table B3648, or it has a sliding stoich AFR B3601 table.

PE will be ok because it is like a multiplier/divider.

[ or if you use EQR units you will see the relationship between the PE and OL fuel tables ]