Reset Fuel Trims ??

[the blur]

My 2013 Burb 100% stock. Wouldn't start correctly, Ran terrible when cold. Rough idle.
Eventually after 2 trips to the dealer, they reset the fuel trim. They say it was sensing alcohol based fuel.
I was getting rich codes on the o2 sensors.


Now it seems to be ok. No parts replaced, just reset fuel trim.

What gives ?

 

[sumo]

Flex fuel sensor. If it thinks it E85 the pcm will compensate for the fuel mixture. Other things that can give you symptoms like you described is unmetered air, like a air leak. If the values are incorrect the pcm will dump more fuel because it dosent know how to compensate for the uncalculated air.

 

[swathdiver]

I'd say keep an eye on it but you cannot without a Tech2. Get a Tech2. It's possible though unlikely one or more of your O2 sensors is not 100% anymore but not bad enough to throw a code. It could be the fuel; the trucks don't like to constantly switch back and forth between regular gas and E85.

 

[lamerem]

I run both E85 and regular and have had no issues.

 

[Doubeleive]

ive never tried e85 its just not even on the menu around me at all closest place is 36 miles away in downtown sacramento

 

[lamerem]

I rather like the taste of E85. The truck is peppy and very responsive when using it. It does offer a bit of extra power by design and is noticeable.

 

[sumo]

But the efficiency/miles lost though

 

[swathdiver]

But the efficiency/miles lost though

Right now, in my area, it costs less per mile to run E85. Sure the range is shorter but the fuel is much less in price. 93 octane costs me $.21-27 cents a mile and E85 $.16-.19 cents a mile. If the price gets too high it won't make sense from a money standpoint to run it. The engine sure does like it though.

 

[lamerem]

When I ran regular gas my Tahoe was very sluggish off the line. Almost hesitant would be more like it. I called GM customer support and spoke with a pretty smart fella who pointed me in the way of E85. He said that the only difference in the 5.3 Flex and the 5.3 regular gas engine is the programming in the computer. That being said the gas model is programmed for gas, obviously. However the Flex model is optimized for E85 1st and gasoline 2nd. Taking his advice I tried it. Now, that being said I get less mileage, but I didn't buy a Tahoe for the mileage. Being that I live in Iowa, E85 is much more readily available than some other places.

 

[swathdiver]

Matt, that fella at GM gave you incorrect information. A FlexFuel engine has different materials for some parts of the fuel system and has larger fuel injectors and maybe even a bigger fuel pump. The computer regularly measures the alcohol content in the fuel tank and adjusts performance based on that and other variables, so it can run great on high octane fuel as well. Your truck was sluggish probably because you were using 87 or 89 octane fuel which strangles these engines, they have to pull timing to keep from knocking.

Out of curiosity, how much is E85 running per gallon up there and what is the alcohol content? Down here it had fallen below $2 a gallon but this holiday week it's just over that and the alcohol content has remained at 62% from the Racetrac stations that we've been using.