E85 in Silverado, Check Engine light!!!
 

My friend Joe has a 2004 Chevy Silverado with a 5.3 liter V8 in it, it is bone stock. He called me the other day to ask me what I knew about E85. I said, "not much...why?" He told me he was at this local gas station and they had E85 and it was something like 50 cents a gallon cheaper than regular 87 octane fuel. So he asked the guy at the gas station if it was ok to run it in his truck, and the guy didn't say yes, but he didn't say no. Joe told me he filled his truck up with it anyway. He drove 1 mile down the street and his check engine like came on.
What are your thoughts as to what happened to this truck? I know a lot of you guys praise E85. I honestly don't know enough about it to even have an opinion.

Is his truck E85 compatible? Quick Google search said not all Silverados of that year were.
--Alex

I don't think it is. I have a Silverado with a 4.8 and it's pretty much the same thing as his truck and mine's not compatible.

http://autorepair.about.com/od/enginefuel/a/111705.htm

Shows compatibility for the '04s by VIN code.
--Alex

Probably something in the neighborhood of P017x for "fuel trim malfunction" or "system too lean."

Basically, the O2 sensors went full lean when it started burning the new mixture, so the ECU started bumping up the short term fuel trim until it hit the limit. There's a maximum range (both positive and negative) across which fuel trim is allowed to operate, and if the ECU hits this limit and the sensors are still showing too lean or too rich, it's considered a fault condition.

With E85, the energy density is considerably lower than for gasoline, so you need to flow a much larger volume of fuel to achieve the same lambda value. The fuel table on that ECU is tuned for gasoline, so at the flowrates it considers "normal", the E85 is burning way too lean. It tried to compensate by increasing injector duration, but the limits on the amount of positive trim it can apply prevented it from achieving stoichiometric combustion.

Drain the tank, install a fresh batch of regular gasoline, and reset the codes. It'll be fine.