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E85 Fueling Goof

Fireman Ed

By Fireman Ed
in Ask A GM Technician

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Fireman Ed Enthusiast

Fireman Ed

Posted
Posted

Ok, so let's say you found this forum and the thread about having to drive 7ish miles after fueling after you already improperly fueled and mixed fuels. I have noticed less fuel economy than before, and when the traction control get's really mad (icy roads) when pulling away from a stop, I am pretty sure I hear backfires comming from under the hood.

 

Now what can I do to get the computer to start over with it's math?

 

"If it is more than 15% off then the tank MUST be dropped down, emptied and dried out and an initial refuel event needs to be done. If that fuel is not E-10 or E-85 it must be disposed of. "

 

Can I force an "initial fuel event"? I know that the last 20 tankfuls have all been E-10, so I am sure it is e-10 in the tank.

Thanks for the help

Fireman Ed

 

08 sierra crew

66nova Senior Enthusiast

66nova

Posted
Posted

So did you top your tank off with E85? I'm not sure I understand...Describe this backfire a little more.

 

You can disconnect the battery for about 10 minutes and that should reset your computer.

Fireman Ed Enthusiast

Fireman Ed

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  • Author
Posted
So did you top your tank off with E85? I'm not sure I understand...Describe this backfire a little more.

 

You can disconnect the battery for about 10 minutes and that should reset your computer.

 

yes, from topping it off a few times with e-85 and not driving more than a mile

I now only use pump gas (E-10), it sounds like a backfire from inside the cab, kind of a bump noise. I realize the ABS vibration noise it there, but this is a bumping noise like a backfire sounds from inside the cab. I haven't heard it from outside as my wife refuses to to drive it cause it is "HUGE". (not the first time I heard that, lol)

Nick The Great Senior Enthusiast

Nick The Great

Posted
Posted

My understanding, from my E85 troubles with my Blackbear tune, was that you have to put in the 15% of the tank, and it automatically recalculates.

 

My trouble was that I had a tank full of E85 and my new ECM was under the impression it had no ethanol in it. So no matter what, the ECM never got an "increased" ethanol concentration, therefore never adjusting it's tables. I solved it by putting in the old ECM until my tank was practically empty, put in 87 octane, and THEN swapped 'em.

 

The problem is our GMT900 trucks don't have an ethanol sensor like the GMT800's did. It just adjusts its timing or whatever based on how the fuel burns, incidentally accounting for Ethanol, Methanol, etc. I personally know a great deal about Ethanol (and alcohol in general, for that matter :eek: ) but I don't know a lot about how GM Flex Fuel vehicles work.

 

I don't know the answer to your question, which is why I never replied last time you asked. It is supposed to readjust after 15% tank refill, and definetely should after a tank. I'm wondering if somehow your ECM is messed up. I think you may have to call the dealer.

 

Good luck and keep us posted :cheers:

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