Woah Laloosh...you may not agree but that is exactly how these cars run. This is how ALL adaptive fuel strategy ECU's work.
Now granted, you are partially correct saying that a partial throttle map is within the ECU, and the ECU seeks a stoich tune. No doubt about it. But, how it does it is different then you are saying, and you must address the LTFT and STFT issue.
(lifted from sources regarding the issue)
With Closed Loop (CL) control, the ECU has feedback to tell it whether it hit the desired A/F ratio target or not (well, sort of, as we'll find out). At part throttle, when the engine runs at the stoichiometric (chemically correct) A/F ratio (required for minimum emissions, and maximum catalytic converter efficiency), the combustion products should ideally be only water vapor and carbon dioxide. If the A/F ratio was a little lean (too much air and/or not enough fuel), the excess (unburned) oxygen will show up in the exhaust gases. Using an O2 sensor, the ECU can now detect when the engine is running lean. Vice versa on the other side, running rich.
So what happens when the engine is running rich and there is no oxygen in the exhaust? The ECU will assume that if there's no oxygen present in the exhaust, then the A/F ratio must be rich. At that point, the ECU makes a conscious decision to lean the A/F ratio, that is, until it reads oxygen in the exhaust again. At that point, the ECU knows it went too far (it's now lean), so it will richen things up again until the oxygen disappears, but now it's rich again, so the ECU will again lean things out, and so on. In CL mode, the ECU will continually cycle the A/F ratio lean, then rich, over and over, hovering the A/F ratio closely around the stoichiometric point.
In CL mode, the ECU will still go through its normal PW calculation, then adjust the PW if necessary, based on what the feedback loop (O2 sensors) is saying. Any adjustment to the calculated PW is handled by the ECU as a Short Term Fuel Trim (STFT). With modern (second generation) On Board Diagnostics (OBD II), many ECU parameters can now easily be logged in real time, including the STFT. Depending on the ECU and data-logging system being used, STFT can be reported differently, sometimes as a plus or negative percent (minus STFT meaning the engine is running lean, so the ECU is reducing its calculated A/F ratio in order to get the actual desired A/F ratio), or as a number around 1.00 (STFT numbers less than one, meaning the ECU is correcting a lean condition).
Adaptive Strategy - If the ECU constantly needs to shorten calculated PW to achieve the desired A/F ratio in CL mode, it knows its programming is calculating a PW too long (possibly from erroneous sensor inputs), and it will remember that correction for next time it makes a PW calculation for the same operating conditions of load and rpm. In other words, the ECU actually learns. The remembered corrections are known as Long Term Fuel Trims (LTFT). The LTFT work oppositely to the STFT, i.e., a plus LTFT (or LTFT greater than one) indicates the ECU is adding some to the calculated PW, in order to get the A/F it wants, based on what it's learned in the past.
Even though the ECU only knows it's hitting the desired A/F ratio when the A/F ratio is stoichiometric (in CL mode), the ECU can also apply the learned corrections (LTFT) any time the ECU is operating in OL mode, and commanding an A/F ratio other than stoichiometric. This Adaptive Strategy allows sensors to age and drift in their readings, but the ECU can now correct for the errors, and still hit the desired A/F ratio in the end.
In the real world, adaptive strategy can be a problem. For some ECUs, corrections learned at one set of operating conditions (e.g., idle) are also applied under other operating conditions (like high-rpm WOT). In that case, if you have a MAF sensor that reads too rich at idle, a leaned idle correction is learned, which if also applied at WOT, can spell disaster. For these applications, it's necessary to either rework the adaptive learning table in the programming to prevent learned corrections from being applied under other operating conditions, or make certain the MAF sensor calibration is corrected. The least desirable, last-ditch technique is to disable adaptive learning in the tune. Whichever way, a custom tune is required.
Closed Loop mode (and Adaptive Strategy learning) is usually only active during part throttle modes, when the engine and O2 sensors are up to stabilized temperatures, and the goal is an A/F ratio right at stoichiometric. During the first few minutes after the engine is first started, and during high-load periods (like WOT) when a richer A/F ratio is intentionally desired, OL fueling strategy is typically used. Thus for maximum power, we need to ensure the ECU calculates the correct OL injector PW, so we get the WOT A/F ratio right. This is where a proper tune comes in.
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Here's another take on it as well:
There is much confusion about how Adaptive Control works especially at WOT. Adaptive control, is always functional at WOT and anything less than WOT. The difference is that in open loop and at less than WOT, this feature monitors O2 sensors and writes correction trim factors to Keep Alive Memory, which are applied to the base table value for future calculations. This is accomplished by varying injector pulse width. The rate at which Adaptive Control writes these correction factors to KAM is slow enough to filter out short duration upsets in the mixture. Short-term closed loop corrections are written to Long-Term Adaptive Strategy KAM if they are repeatedly seen out-of-spec by the O2 sensors. At WOT the Adaptive Control still functions but it does not update (or write) correction factors to KAM for application to the base tables it defaults to the already stored trim values, if any have been written, for the load and engine temperature experienced in the WOT load range.
Also remember, the corrections are limited to about 25%, so if you change fuel calculations beyond the ability of the ECU to correct, it will not be able to tune out your changes.
-= Hope this helps... we need to understand the system fully if we are to take advantage of it!
