The LH “Adaptation” value (two actually) is the long-term average of the LH’s O2-adjustment (see To Adjust and Adapt). If everything is perfect– MAF correctly calibrated, fuel maps correctly adjusted, O2-sensor working properly– then O2-Adaptation will be close to zero. The adaptation values change slowly (minutes) and is saved in LH memory when the ignition is off (and reset to zero if the battery is disconnected, even momentarily).
When operating in closed-loop mode, the LH is always changing O2-adjust up and down a few percent to keep the mixture around 14.7 in response to the O2-sensor. As MAFs age, for example, they read lower air flow which results in a weaker (more lean) mixture, and the LH responds by increasing the O2-adjust value to compensate. This changes the average O2-adjust, so the LH changes the O2-adaptation values accordingly, moving the average O2-adjust again towards zero.
So there are two parts to this story: The moment-to-monent O2-adjust, which is active in closed-loop mode– idle and light load– and the saved O2-adaptation values which are always active.
For adjusting the fuel map, O2-adapation should be disabled and reset to zero on Sharktuner’s fuel-parameter page. We don’t want the “help”, we will be making those changes ourselves. We also want the CO-Pot disabled particularly if there is not one fitted.
Once we are finished adjusting the fuel map, do we want to re-enable adaptation, or leave it disabled?
In almost all cases, O2-adaptation should be re-enabled once tuning is finished. There are two reasons:
- First, if adaptation is enabld, then a quick look at the Fuel Monitor page will tell you whether there is a problem or not. If the adpation numbers are close to zero (say within 5% or so) then the average O2-adjust in closed-loop mode is small, and MAF, temp sensors, and O2-sensor are all working as expected.
- As things age (the MAF in patricular), the LH compensates as usual during normal driving with O2-adjust. But remember that O2-adjust is only active during closed-loop operation, idle and cruising with light to moderate load and RPM. For wide-open throttle O2-adjust goes to zero. So if the LH has been happily adding an average of 10% additional fuel to compensate for a weak MAF, then at wide-open throttle that goes away and the engine is short 10% of the fuel that was intended. With O2-adaptation enabled, that extra 10% becomes the adaptation values, and continues to be applied for WOT.
- The total range for O2-adjust is ±20%, and adaptation is another ±20%, so 40% total compensation. That’s a lot, but MAFs can get pretty far out of spec. (And yes, that’s three reasons).
Why are there two adaptation values?
The fuel tank is vented through a charcoal cannister, which traps fuel vapors. And the canister is itself vented through a valve to the engine intake during periods of high engine vacuum, to burn those vapors. This venting is unmetered air (i.e. does not pass through the MAF), and changes the O2-adjust a small amount (a few percent). And because the LH knows when this vent is open, it can maintain a separate average for vent-open versus vent-closed. The two numbers should always be within a few percent. Remember, anything worth doing is worth over-doing.