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I have my 2008 Challenger set up for E85 with FA Stoich being .1020 and PE being .0265. I recently got a great deal on a bunch of E90 and I would like to run that. Should I have to modify FA Stoich or PE? I do not think so as that is not a big difference. I am tuning with AFR vice lamba.
Well, the difference in lambda would be close to 3 percent. You can add 3 percent to the fuel tables or just leave it as it is now. One thing to remember is that the closer you get to 100 percent of ethanol content the harder it will be to start up the engine in weather below 11-12 degrees C as ethanol isn't very ignitable below that temperature - that is why we add petrol fuel to that mix.
Scott,
You're changing the stoich value of the fuel, so I would update the stoich value of the fuel in the tune rather than fudging MAF or VE tables, or PE.
Power enrichment likely won't need altered between the two as I don't typically target significantly different lambda values on 85 vs 90% ethanol aside from a little at cold start/warmup which may not be necessary in your case.
By updating the stoich value for E90, the fuel mass delivered will increase for any condition, and you should achieve the same result lambda values you were before.
@MikeMcGinnis and @georg1970 Thanks for advice! I will update FA Stoich to .1052 for the E90 and let the pcm do the rest. You guys rock!
