Originally Posted by Kabigon
Here is some interesting reading on this subject:
In order to maintain proper fuel control, the PCM strategy needs to know the stoichiometric Air/Fuel Ratio for use in the fuel pulse width equation. On pre-2000 MY flex fuel vehicles, the percent alcohol in the fuel was determined by reading the output of the Flex fuel Sensor. The percent alcohol was stored in a register called Percent Methanol (PM). Although current alcohol-blended fuels only include ethanol, the percent methanol nomenclature has persisted. On 2000 MY and later vehicles, the Flex Fuel Sensor has been deleted and PM is inferred. The strategy to infer the correct A/F Ratio (AFR) relies on the oxygen sensor input to maintain stoichiometry after vehicle refueling occurs.
(see pages 62-63)
Good read. So what I'm saying sounds like it really applies to 2000 MY and up. However, wideband data only became available in most Ford models over the last 3 MY's, and as little as 1 MY in this case. So, lambda wasn't available.
That's interesting. The tough thing is that I've never actually seen the logic they're claiming in any PCM codes. This is probably because I never tune flex vehicles and always tune gasoline, E10 or E85.
I need to dive into a flex fuel PCM code.