Filled up my sisters E85 Yukon ...now runs like crap.

[Fless]

Mine says L59 as well and I know my engine is a flex fuel.

My L59 is Flex as well (all L59s are), Flex also indicated by the 'Z' in the VIN.

 

[HiHoeSilver]

The fuel door should also have a small sticker that tells if it's E85 compatible. The RPO code L29 -- that doesn't seem to be a good code. Could it have been L59?

Gotta be L59. All aluminum FFV.

 

[Fless]

All aluminum? My L59 block is iron.

 

[HiHoeSilver]

All aluminum? My L59 block is iron.

Duh, you're right. Why did I think that? I have one. Lol. L33 I was thinking of, maybe?

 

[OR VietVet]

Now I am lost, ALMOST. How many "L" codes are we gonna throw out there? L29 then L59 and now L33.

 

[wjburken]

Now I am lost, ALMOST. How many "L" codes are we gonna throw out there? L29 then L59 and now L33.

BINGO!

 

[gooffeyguy]

Let's not forget L94

2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18

 

[Fless]

Now I am lost, ALMOST. How many "L" codes are we gonna throw out there? L29 then L59 and now L33.

Hopefully not many; GM has hundreds of L-codes for engines. My RPO Master List starts at L01 for engines, and after L97 it restarts with LA1, LA2, and goes on and on. Obviously a small percentage have been in our truck builds.

@HiHoeSilver you're correct that the L33 is aluminum.

 

[danielnorris]

Thanks to those who posted. My wife and I were out on a date so couldn’t respond. I have to clarify that I have never OWNED an E85 capabale vehicle and have zero experience with them. My confusion is because I was told it’s E85 , it has the yellow filler cap stating E85 but no flex-fuel emblems on it. A quick internet search and a GM website came up stating E85 but not flex. Again I have no experience with flex-fuel vehicles.

So I learned that ALL E85 vehicles are flex-fuel (yes..?) and should run fine on even “regular” unleaded. So I have to guess more than likely bad fuel. Although I have to agree the problem should have surfaced before 30-miles of travel. So I’m still confused and still wondering if I should just add good gas and run it....

I’ll check the codes on it when I am able.....it’s not at my house.

Even if the vehicle is capable of running E85 the computer has to be programmed for it to run properly. You can't switch back and forth between flex fuel and regular fuel. I found this out by doing the same thing in my wife's Ford 500. My advice would be to run as much of the fuel out of the tank and refill with good gas and repeat for a couple of tanks. Get ready for some crappy mileage until it gets cleared out.

 

[HiHoeSilver]

Even if the vehicle is capable of running E85 the computer has to be programmed for it to run properly. You can't switch back and forth between flex fuel and regular fuel. I found this out by doing the same thing in my wife's Ford 500. My advice would be to run as much of the fuel out of the tank and refill with good gas and repeat for a couple of tanks. Get ready for some crappy mileage until it gets cleared out.

Absolutely wrong. An FFV is just that... FLEXIBLE in the fuel it can run on. I swap back and forth all the time as do many here.

No tuning is necessary. There is either a physical or virtual sensor that calculates the ethanol % of the fuel and adjusts the tables accordingly.

In the case that you are running a custom tune (I am, for example), one suited for higher octane may produce better results with e85 than an 87/89 tune, as the ethanol can take advantage of the high octane timing, but it certainly isn't required in any way.