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Discussion and questions related to the course Ethanol & Flex Fuel Tuning
In the flex fuel module, it was discussed how air fuel targets for gas engines typically work well for ethanol engines however, it wasn’t directly discussed how to adjust an air fuel target table. My ECU uses trim tables instead of a blend table. Should I run a leaner mixture in idle and cruise or is it not necessary to make any adjustments and if so, why does this table exist?
In terms of lambda, targets will be relatively similar, so it's best to view data in lambda on your tuning software rather than air/fuel ratio, which confuses things since it may always display on gas scale or may not and it's often not clear.
Generally speaking your biggest lambda target changes will be for cold start, and at mid to higher engine loads. Most mild to moderate setups should be able to idle and cruise at stoich afr on gas and E85.
I understand the benefits of using lambda instead of air fuel ratio which I am doing but my main question was what adjustments should be made to the lambda target tables for flex fuel. I don’t recall seeing any practical application of adjusting target tables or blend tables when tuning flex fuel. Like should mixtures be slightly leaner on e85 than pump gas?
To start from my prior post: "Generally speaking your biggest lambda target changes will be for cold start, and at mid to higher engine loads. Most mild to moderate setups should be able to idle and cruise at stoich afr on gas and E85."
You'll need to be a bit richer on cold start.
Changes at mid to high engine loads depend on your specific setup and what quality gas you were running. As Andre states, some setups will use the same high load targets, but some will not.
If you've had to run super rich on gas because it's low quality fuel or your engine was severely knock limited otherwise, then you may be able to run significantly leaner on E85. If the engine ran at/near MBT on gas, you may not end up benefiting from a lambda change at high load.
There isn't one right answer for a high load target on either fuel as this isn't that simple/universal, but I hope this info helps you get going!