E85 -- experience

On Tue, 20 May 2008 15:13:19 -0500, "dnoyeB" <askme DeleteThis @fake.net> wrote:

>On Tue, 13 May 2008 17:44:35 -0700, Uncle Ben wrote:
>
>> On May 12, 11:11 pm, Carl 1 Lucky Texan <alcky... DeleteThis @swbell.not> wrote:
>>> Uncle Ben wrote:
>>> > On May 12, 8:52 pm, Tony Hwang <drago... DeleteThis @shaw.ca> wrote:
>>>
>>> >>If you changed fuel. Wouldn't it proper to disconnect battery and let
>>> >>the ECU learn again?
>>>
>>> It will, learn eventually. But , if you expect HIGHER octane, it is
>>> probably better to force the ECU back to the factory map. Then it starts
>>> from max advance and retards on knock detection. If you don't do that,
>>> and the system has already retarded the timing, it may take a very long
>>> time to advance it, if ever.
>>
>> Thanks, Tony and Carl, for the info on MAPs and ECUs and changing
>> fuels. I had never known about these things before.
>>
>> But what I am doing (when my kit comes) is to convert my car to an
>> FFV. So the design goal is to enable me to change fuels drastically
>> and often. On the road I might be running E85, fuel getting low, and
>> no E85 station within 100 miles. I would then switch to E0, or pure
>> gasoline. That is supposed to be routine. I shouldn't have to
>> disconnect the battery every time.
>>
>> I remember reading that the FFVs detect the concentration of ethanol
>> and adjust quickly to it. I don't know what sensor detects the
>> change, but it must be there somewhere.
>>
>> In my recent experiments before installing the kit, if there were
>> drastic errors in timing and mixtures, I should have experienced poor
>> acceleration, stumbling, or even stalling, not to mention poor
>> mileage. In fact, that did not happen. I can't explain it, but
>> things went very smoothly, and the cars pep and smooth running was
>> great.
>>
>> Cars are getting too complicated for us amateurs!
>>
>> Ben
>
>I doubt they detect Ethanol at all. More likely they monitor the engines
>performance and adjust fuel/oxygen ratio to keep it within some
>performance parameters. I bet they can tell the octane by engine output
>and temperature, etc. Of course, this means the ECU designer must have
>some logic that says E85 is not the engine malfunctioning...
>
>CL
Actually, some vehicles DO have a fuel analyzer on board. Generally
some sort of optical refractometer or transmittance device that can
determine the composition of the fuel to within 13% or something like
that. GM early flex fuel vehicles used this.

The new flex-fuel Impalla calculates the fuel composition every time
the fuel cap is removed by running an algarithm on the O2 sensor data.
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