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.

 

[sumo]

Yea there differences in flex and non. Defiantly has larger injectors and fuel pump. Fuel lines are rubber I believe. Flex also has fuel sensor to detect fuel mixture, o2 and pcm. Flex though is the better choice if you want to supercharge it

 

[lamerem]

That is disheartening! E85 here is right at $2 a gal. I did use 87 octane mainly because everything else is an entire $1 more per gallon. Why do they not compensate for this?


Sent from my iPhone using Tapatalk

 

[swathdiver]

I know, the price difference between low test and high test is greater than ever before but there are some reasons for this. First of all, you have market forces of supply and demand at play, then we know that the premium fuels contain additives that are beneficial to keeping the fuel system clean, lowering emissions and increased gas mileage. In general, it costs less to run 93 than 87 because of the greater fuel economy of the higher test gas. Over the years I've documented at least 2 mpg from anything I drove over time to 6 mpg with certain vehicles and certain brands of fuel. The Prius drivers love to talk about this on their forums, they get 4-8 mpg higher economy not by switching from 87 to 93, but by using one particular brand of 93 over another. They already know that 87 and 89 stink.

 

[RDKill321]

And that brand of fuel is.....

 

[the blur]

So in the mean time, my truck has been running 100% perfect since the dealer reset the fuel trims. I never used E85 at all...
Apparently if the trims get out of whack, they don't automatically correct. Then you get erroneous codes for running rich...

 

[swathdiver]

And that brand of fuel is.....

Mobil is best for me right now. Chevron was pretty good but the only station around charges a small fortune for fuel.

The trims are constantly being checked and adjusted by the computer.

 

[the blur]

The trims are constantly being checked and adjusted by the computer.

Obviously NOT... if I had to have mine reset at the dealer !

 

[swathdiver]

Obviously NOT... if I had to have mine reset at the dealer !

You can watch it happen with a Tech2. I've reset mine too but they're constantly adjusting anyway.

 

[the blur]

You can watch it happen with a Tech2. I've reset mine too but they're constantly adjusting anyway.

I realize that, but mine were so skewed, the truck wouldn't start. They never "normalized".

 

[Teeroy78]

I'm currently in the middle of this problem too. I've never even seen E85 gas anywhere in Manitoba, so I certainly haven't put any in, but after my last tank from Superstore (regular grade) I got P0172 and P0175 with freeze frame data showing alcohol content over 75%. That was on the way home from an errand right after filling up. It eventually settled at 45.5%, and the check engine light would keep coming back pretty often. Too bad because we had a nasty cold snap around Christmas, and a CEL disables remote start.

Fast forward to today where I finally emptied that tank, went to Shell and filled with premium 91 octane zero ethanol, hoping it was just a bad batch of gas. I then headed for the highway and went far a drive, about 40km. Watching the alcohol content bounce around on my BlueDriver, it finally settled at 27.5%, and the short and long term fuel trims are still just as bad as before. I'm sure I'll see a CEL in the next day or two.

I just hate to go pay the dealer a ridiculous amount of money to reset the fuel trims just because I don't have a Tech 2. Depending on what they want to charge, it may be worth it to get an Alibaba Tech 2 and then I'll have something to keep after.

I'm glad to hear that you're still running problem free after your dealer reset.

If anybody is interested, I've attached the PDF of the freeze frame report.