05-29-2007, 08:31 PM
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Active Enthusiast
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Hybrids: Toyota Highlander
Posts: 80
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Re: Premium gas...?
Quote:
Originally Posted by petesell
very good post don.
the only variable i don't quite comprehend is the ecu - how 'adaptive' is it?
does it follow a standard timing map as written into the s/w and simple advance as much as the fuel in the tank will allow? if we run 5 tanks of 87 and then throw in a tank of 93 will we see timing advanced instantly, or is there a 'learning' period for the ecu to adapt?
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The ECM adjusts ignition timing advance via stored memory maps with inputs of engine speed, intake air volume or manifold pressure, throttle position, engine coolant temperature etc.
A corrective ignition timing control function in the ECM makes a final adjustment to the pre-mapped timing settings based on such conditions as engine speed transitions, cruise control operation, traction control activation, knock detection, etc.
In simple terms, the corrective ignition timing algorithm for knock retards the timing in relatively quick discrete steps until the knock just disappears. If knock is no longer detected, the ECM then begins to advance the timing again but now in slow discrete steps. If knocking occurs during these slow advance steps, it again retards the timing in quick steps.
The engine is most efficient using a particular grade of fuel when the ignition timing is fine tuned to the ragged edge of advance just before knock occurrence. At this setting, the engine achieves the best fuel economy, engine power output, and lowest exhaust emissions. The advance timing correction is not glacial in response. The vehicle should correct for a higher octane shortly after filling the tank with 93 octane but not instantly.
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