Emergency switching from e85 to 93 on FAST

gibbstroy

Member
Jan 12, 2018
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Allen, TX, United States
Ive searched everywhere for two days without much luck looking for the possibility of switching FAST xfi from e85 to 93 in emergency conditions. I have e85 nearby but there are several events I want to attend that cause worry about e85 availability, including a race at Texas Motorplex tonight!

Ive tried to contact Cal Hartline the last few days, the original tuner, but he must be pretty busy. Is there a fairly simple way I can make an adjustment on my laptop to utilize pump gas to make it home (low to no boost) at highway speeds without needing a fuel 93 octane tune? I do have the latest version of FAST.

I recognize the benefit of running an e85 sensor with FAST and Ive already ordered one. But tonight the track is just far enough to make me wonder if I can make it with such a small fuel cell.
 

pacecarta

MAGNA
Staff member
Aug 1, 2003
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RIP racewaypark, NJ
for driving, just go into ccom program and select view > system configuration >fuel calc parameters and change Fuel Energy Constant from .68 (e85) to 1.00 (93) and just stay out of the high boost

if on cals tune if its one of his 2.05 tunes the timing should drop when changing FEC but just for safety sake you could also check your timing vs FEC table (view >spark timing >spark vs FEC) and it should drop as fec rises have 0 at .68 and be around 2 degrees less timing at 1.00

if you have 2.05 install a flex fuel sensor in the return line and the program will make the changes on its own when it detects the change in ethanol
 
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pacecarta

MAGNA
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Aug 1, 2003
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note the 1.00 fec is what normally gets used whe running pump gas even though most 93 pump gas has 10% ethanol (its really E10) with a flex sensor you will never see 1.00 and when adding 93 to a tank that has some e85 in it you may need a little adjustment for the percentage of e85 so you may find that .85 - .90 FEC is closer to whats in the tank
 
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pacecarta

MAGNA
Staff member
Aug 1, 2003
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RIP racewaypark, NJ
save your e85 tune before you switch the settings or fuel , the 93mix may make some changes to your e85 VE table with the learn enabled and one other thing that might help is to drop the learn rpm so it can fix the idle area VE allowing it to adjust for the fuel variation beyond what your normal correction limits may be , once back on e85 load the old tune
i know your getting the flex soon but if you werent id suggest that once youve driven it with the 93 you can save that 93tune with the FEC changed and the ve learned and load it up for your next trip and your tune will be be closer
 
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