Hello all, new user and clueless tuner here. I have a 1.8t that I would like to Flex Fuel tune. I currently have it tuned for 91. After excavation of the Internet I have a basic idea of how the process works. My understanding is there is 2 strategies that can be used?
One being enable flex fuel and enter a percentage in the (Ethanol fuel scale factor) while only using VE map #1 ??
The other being enabling flex fuel and tuning #1 VE table 91 octane, and selecting blend VE tables while having the #2 VE table tuned for the highest percentage of ethanol I can achieve.
If I am correct in my assumptions if I was to use both VE tables do I still need a number in the (Ethanol fuel scale factor)?
Lastly would that factor number be for example 175% if 75% ethanol was my maximum?
In my opinion there is only one correct way and that is first one you mentioned.
The volumetric efficiency of the engine (as defined by the VE table) shouldn’t change as a result of a fuel change. The fuel dose calculation in the background will change however based on that fuel scale factor to account for the different Stoichiometric air fuel ratio’s between the fuels.
A number around 157% for the fuel scale factor has worked for me. That number comes from the additional fuel dose required if you were to run E100. for example at 85% the fuel dose will change by 157% x 0.85 = 133.45%. This is all done in the background based on what the flex sensor reads.
You MAY still need to blend VE tables once you go to tune it but the difference will be minor. Say you start to run out of fuel system once on E85 you may need to artificially inflate the VE #2 table numbers to keep your fueling on target. In theory however, one VE table will do the trick.
Ethanol fuel scale percentage works well if your using it for Ethanol blends and then you can use the VE Table 2 for fine tuning if needed.
But if you want to use the FlexFuel for Methanol blends you will have to use VE table 2 and blend because the fuel scale percentage will only let you add up to 200% where as with methanol needs more than that, it would be good if that limitation was removed or extended.