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Having a standalone ECU is not a must do. My 300zx is already flex fuel (but most of the time I run 100% E85), it used OEM ECU but I modified the code deeply: it uses OEM narrowband lambdas sensors and obliges to have the car idling 1-2 mins after having filling the tank with some unleaded. It works like a charm: ECU goes back to 14.7 AFR in idle very quickly, so the ECU automatically compensates K value accordingly.
Of course I have widebands in front of my eyes to check the ECU reacts fine each time.
My K centered value on E85 is 200, with my flex fuel code, the value oscillates b/w 192 and 216 when running 100% E85 depending on outside temp, engine temp, density of air ... when putting unleaded, it may goes down to 144-160. ECU auto-adapts ! You don't need to switch maps, really. You tune first for 100% E85 (timing/fueling, cold/warm start maps, ...), and even if your put 50% unleaded one day, it's not a problem, there's still enough ethanol overall to support the advanced timing, and in case of knock, the OEM ECU does this job of retarding timing, up to 7° before switching to knock map(s). I still produce sometimes some knock when flooring on cold days in the 2000-3000rpm area: heavy load, but my timing tune is at the limit of knock on E85... a bit of knock (and ECU retards ..) is not really a problem when running E85.
I target 11.5-12 AFR when flooring and it goes back quickly to 12.5 on sustained boost (15.5 psi). I reach TP=81-82 in winter with 740cc and have 21° BTDC @4400rpm in the 16th column of the timing map.
I've run E85 on the 300zx since 2007, so I have a bit of history on it and many logs, I even noticed targetting a richer AFR on full boost (11-11.5) makes some knock occuring ! Wiring a flex fuel sensor (GM or Haltech one) to my OEM ECU (using spare inputs of the ECU) and adding code inside to support just makes the things more accurate, I'm working on it.
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14:24:54 09/20/12
