E85 + 91 Octane
Some tuners will adjust the A / B / C / D closed loop load ranges that the ECU uses to set fueling trim adjustments so the D range never changes. The D range also trims the open loop fuel map, so if a map is done this way, then open loop can go too lean with small amounts of E85. This is not really the proper way to tune pump gas, but some do it that way. Anyone who tunes E that way is kinda crazy, since the ratios coming from the pump are unpredictable.
Any decent tuner who is aware that this will be a map for use switching back and forth will make sure the D range fuel trim adjustments will be in effect on the 91 map, and then it will be fine to run E85 in low ratios on that 91 map (switching tanks). You just need to let the ECU adjust it's fuel trims to your blend before you start beating on the car.
Any decent tuner who is aware that this will be a map for use switching back and forth will make sure the D range fuel trim adjustments will be in effect on the 91 map, and then it will be fine to run E85 in low ratios on that 91 map (switching tanks). You just need to let the ECU adjust it's fuel trims to your blend before you start beating on the car.
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I definitely don't recommend switching between the two fuels often, but its not the end of the world to do it on occasion if you're careful.
-- Ed
-- Ed
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Some tuners will adjust the A / B / C / D closed loop load ranges that the ECU uses to set fueling trim adjustments so the D range never changes. The D range also trims the open loop fuel map, so if a map is done this way, then open loop can go too lean with small amounts of E85. This is not really the proper way to tune pump gas, but some do it that way. Anyone who tunes E that way is kinda crazy, since the ratios coming from the pump are unpredictable.
Any decent tuner who is aware that this will be a map for use switching back and forth will make sure the D range fuel trim adjustments will be in effect on the 91 map, and then it will be fine to run E85 in low ratios on that 91 map (switching tanks). You just need to let the ECU adjust it's fuel trims to your blend before you start beating on the car.
Any decent tuner who is aware that this will be a map for use switching back and forth will make sure the D range fuel trim adjustments will be in effect on the 91 map, and then it will be fine to run E85 in low ratios on that 91 map (switching tanks). You just need to let the ECU adjust it's fuel trims to your blend before you start beating on the car.
This is mostly correct except that the long term trims in that upper range can be somewhat unpredictable and can take a long time to adjust appropriately. The main problem is that you have to drive for extended periods right in that spot of the MAF curve to effect the D range which will extend to the OL area. Even then, it will not necessarily effect the entire OL area. There is sadly no perfect fix for this without full closed loop fuel control or an ethanol content sensor.
-- Ed
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I've been thinking about it more....
This thought came up for me because I've been very limited on where I can go and I've missed out on a few road trips because of the limited E85 stations.
I would just stay on E85 now for DD. If I decided to drive my girl on long trips, I would run the E85 as low as possible then switch over to the 91 map.
This thought came up for me because I've been very limited on where I can go and I've missed out on a few road trips because of the limited E85 stations.
I would just stay on E85 now for DD. If I decided to drive my girl on long trips, I would run the E85 as low as possible then switch over to the 91 map.
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specb
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Sep 12, 2006 01:56 PM
