ORIGINAL: glens

Thanks, CDN. RG.

None taken. And I apologize for the stilted language. I am currently avoiding contractions because I dislike the stuttering apostrophes. Am overusing italics to avoid quote marks for same reason.

I guess I do not know how to layman up the language any more than I have but will try.

Whenever the ECU has to add or subtract fuel to reach its target O2 voltage while in closed loop, it stores that difference, from the amount of fuel it thought it should have sent, as a factor for figuring future fuel amounts. It will use that factor everywhere, even in open-loop modes, because normally that would be the correct thing to do. (If you are consistently rich because your air filter is dirty, or if you are consistently lean because you bought a tank of oxygenated fuel, the condition as measured during closed loop would certainly be present by the same amount even when the ECU cannot sample the combustion.) This factor is referred to as the AFV.

In another recent thread where a guy asked about trying some older Screaming Eagle mufflers I covered a lot of this stuff in very simple language. It was a couple of days ago. Here.

With these devices in place, the ECU will have to factor in more fuel because its target O2 voltage is now the result of the devices and not that of the O2 sensors. This more fuel is what makes for better driveability and cooler running for the bulk of the time you are cruising around. Whenever you are using the engine in modes where the ECU programming was already rich-enough (and those areas certainly do exist, even on a completely stock bike) it will there/then become too rich. Possibly acceptably too rich, though still ideally too much, when using the standard devices. Likely way too rich when using the extreme ones.

And like I have said many times already, the extreme IEDs do not leave enough wiggle room within the sensor operational range. Look at a graph of a sensor output. So long as it is operating anywhere in the steeper middle range, where a moderate change in air/fuel ratio results in a moderate voltage change, it will be fine. Once it gets to the flatter part of the curve at either end, a very small difference in output voltage covers a wider and wider range of air-to-fuel ratios. At the edge of the curve, a tiny difference in voltage can cover a range from mildly rich to stupidly rich.

The standard IEDs still leave reasonable wiggle room within the sensor output curve. The extremes flat out flirt too heavily with the edges.

Once the limits of the AFV correction (extra fuel) have been reached, the computer throws an your cylinder is running too lean warning code. Remember what I just said about the sensor operating in and out of its linear range. A couple percent difference in fuel might show as a couple millivolts in the middle, but at the edges of the sensor range a couple millivolts might easily represent/require double digits of percentage change in fuel.

ORIGINAL: CNC WHEEL GUY

Wow!&nbsp\\;\\\\\\; Must be glad that was fixed!

ORIGINAL: Ultrasweet

So Glens, in your opinion what is the best value for improving performance on the 08's?

ORIGINAL: mile high king

Love this thread! Seriously. I don't quite understand it, but like many of us that have changed the air filtern and pipes want to know what would be best for the engine if no EPA was involved! Additional questions...how does the V&H FuelPak improve the equation? Is it enough? BTW, stock engine, SE air-clearner and V&H ovals.

Second questions, why is this so hard with a Harley? Why couldn't they (or the aftermarket) just put more range in the o2 sensors to begin with? Don't like driving around baking the crap out of my motor!!!