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e85 flex sensor tuning advice

740atl

Gear acquisition syndrome
Joined
Apr 17, 2010
Location
USA
I'm running a flex sensor in the ol girl and having some issues. This is a b234f+t.

I'm just using the basic flex settings as shown below. I'm letting MS add fuel and timing based on the ethanol percentage and it's not working out that well.

I have a well tuned e10 pump gas map that I use as the baseline and in theory MS will add fuel/timing based on ethanol% but as soon as I empty the tank and fill it with e85, the fuel additions are kind of all over the place. I find I have to retune the map, especially at low rpm and high load/rpm. My understanding is that it should be a linear transition, but it hasn't worked out... it's just too coarse of a process. I've modified the fuel multiplier from 163 down to try to match the tune with the pump gas but it still doesn't transfer well.

Is it possible the additional timing in the high MAP/RPM bins is causing me to have to retune? From what I've read, timing shouldn't affect AFR but I am adding over 10 degrees of timing at 200kpa than with pump gas.

I've considered using the flex blending so I can have a dedicated fuel and e85 VE and spark table, then adjust the blending curves to mix.

Thoughts?

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