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So after buying a brand new cone filter, I've almost got my long term trims dialed in with this GT28 program. Both were within 1-2% +/- However, yesterday the trims went back to -5% and as low as -7%. The only difference that I can think of is that maybe filling up with normal old 91 octane did it.

My theory so far is that the 10% ethanol 94oct gas puts a little more O2 downstream in the exhaust. If that is the case then wouldn't the engine increase the amount of fuel (i.e. up the trims) to compensate? Other than that I'm at a loss.
 

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Hi T,

I was under the impression that fuel blends vary a fair amount, in general. It looks like you changed the trims about 4-5% which would be about the amount of change in air/fuel when going from a non-ethanol blend to an ethanol blend. If you put in normal non-ethanol 91 octane, you would not need to use as much fuel. Or it could be batch to batch variation. Your mileage may vary ;).
 

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YMMV, indeed! *Laugh*

The problem with the new 'environmentally friendly' ethanol blends are that, though the octane goes up (anti-knock, more aggressive timing), they don't give you the same amount of explosive power for the same amount. So to go the same speed, you need to use more fuel. I didn't really notice this much on a recent trip through New York, but I drive pretty thriftily anyway.

My plan for my 93 APR chip, since we only have 91 down here, is to mix up some Xylene and/or Toluene to boost my octane, yet not lose any power.
 

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E10 pushes the fuel trim up by about 3-5%, IIRC.

Troy, you could just add a water injector to increase the octane rating of the air:fuel mixture. It wouldn't give you any more power, necessarily, but if you wanted to you could still advance the ignition timing a bit, and you wouldn't have to keep buying bottles of nasty chemicals either -- just top off the washer fluid once a week.
 

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i've never logged the diff between E10 and E0, but holding everything constant, I'd exoect it to need more E10 to get the same AFR. When I fooled around with E85, the car required substantially more fuel to get the trims settled in. Before adjusting pressure, the trims went way lean, >+20%.
 
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