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long term fuel trims don't really do much except use the 02 sensors to set the AFR to 14.7 near idle. at higher load & RPMs, the (narrow band) O2 sensors can't really tell what the AFR is. the ECU uses the MAF to calculate, using a table, how much fuel to send based on a trimmed out 14.7 idle AFR + some offset values.
once you are over about 3k RPM and 30% throttle, the fuel amount is basically an educated guess based on MAF readings and offset tables.
since my engine will perform so much differently at wide open throttle (WOT), there is a good chance that the ECU tables won't get me to the right AFR's. there really is no way to know without measurement.
on another note, my logger came today. pretty slick piece of equipment! i fired it up to look at my fuel trims and MAF readings. fuel trims are small (<3%). one interesting note: the MAF at idle should be around 15 kg/hr. mine is over 20! so, at least at idle, i am flowing a LOT more air than stock. my guess is that flow advantage decays as RPM's go up, so i am likely getting way too much fuel at high RPM/Load values.
i will get the wideband hooked up & start logging later in the week.
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