ok, i'm trying this again...so far nothing crazy has happened but i only have a few gallons of E85 in the tank and a few miles since i enabled flex fuel. the composition hasn't moved either. I'll report back tomorrow.

 

Cool, I'm glad to see you giving it another go Let us know how it goes. There's no good reason that I see why it should limp, just cuz you enabled FF. Watch your fuel trims, as they will have to move significantly for it to adjust the composition settings. You might need more E85 in the mix.

 

yeah, unfortunately when I finally decided to do it I had a full tank of 93. I drive 50 miles a day though so I'll top it off with E85 on the way home and I figured that should be enough to trigger it. roughly 5-6 gallons.

 

Sweet... I'm really looking forward to hearing how it turns out!

 

nothing yet. i put in 8 gallons of e85 yesterday and today my fuel trims are pretty far out of wack. LTFT's in the 15-20% range. It has not adjusted stoich or shown any readings for the fuel compisition.

 

You must change the stoich values. The computer does not change them. A good tuning book will tell you the base E85 stoich value. It is approximatly 9.76. If you have a spot in your computer for "Power Enrich" you can subtract a full point (making it richer) to 8.XX.

Below are the factory E85 values out of my E85 '07 5.3 Avalanche. Stretch out the Labels and Stoich numbers to make two rows in a spreadsheet and you have it. The "labels" row is actually the percentage of E85.

Labels 0.00 6.25 12.50 18.75 25.00 31.25 37.50 43.75 50.00 56.25 62.50 68.75 75.00 81.25 87.50 93.75 100.00
Stoich 14.67822 14.32227 13.96582 13.60986 13.25293 12.89697 12.54102 12.18408 11.82813 11.47217 11.11523 10.75879 10.40283 10.04688 9.68994 9.33398 8.97803

Depending on your computer version, you may only be able to enter one Stoich number.

But, I have found that only a little bit, say 20%, of E85 in a tank of regular 87 octane can dilute the fuel and hurt gas mileage. Thus, I tend to run tanks of one or the other.

I run E85 in my '06 GTO all the time as it's cheap gas. No issues. Strangely, the E85 built '07 Avalanche has thrown an engine code with E85. I suppose the sensor didn't read the fuel correctly. Oh, and the Avalanche uses 243 series heads just like the GTO. No special valves or seats. The Stoich number in the GTO is a straight 14.69.

If nothing else, use a wide band air/fuel measuring device to check your changes. What comes out the exhaust is what you might want to target.

 

anyone ever confirm this for the GMT900?

 

i was running E85 . with my tune .. and started having problems with that gas . . getting misfires all the time .. . so Im running 93 now .. if you run E85 your MPG will decrease alot ' . ... it takes alot of energy for E85 to match the same Hp of 93* if your gonna be running ur truck I reccomend you 93*

 

The question was weather or not the truck can determine your % of Ethanal IF it wasn't made for E85. My stoich values in my 4.8 were filled out as you posted above. But it won't come off the 14.67 value unless it knows that there is E85 in the tank. And in my case it was never able to determine that.

Obviously you can change the 0 figure to be match whatever percentage of E85 you have in the tank...but it would have been nice to not have to do that.

 

and my question is, are the lifters any different than a dod motor?