The term “O2-Adjust” (or just adjust or adjustment) refers to the real-time adjustment of fueling by the LH in response to the factory O2-sensor (NBO2). The O2-sensor is a simple device which indicates rich or lean relative to AFR of 14.7:1 (lambda=1 for gasoline). There is no history or memory for O2-adjust, it lives “in the moment”. “Adaptation”, on the other hand, is the long-term average adjustment needed, and is stored in LH memory.

There is no point in trying to set the fuel maps for anything richer than 14.7 in the light-moderate areas where the O2-adjust is active (i.e. “closed-loop”). All that will do is annoy the LH, which will simply remove the excess fuel. This is not a problem unless “O2-adaptation” is enabled (which it should be, once tuning is finished). O2-adaptation is a stored long-term correction to the fueling, similar to O2-adjust except (a) is a long-term average, and (b) is active all the time (if enabled), even at high load and WOT.

So if the LH spends a lot of time reducing fuel in general (because the maps were set “rich” in the areas where the O2-sensor is active) then O2-adjust will wind up negative, trying to removing that excess fuel but applying the correction everywhere– which is NOT what you want at high load and WOT. So watch the fueling, and if you see O2-adjust removing fuel from too-rich map cells, then adjust those cells to a target of 14.7.

This map from Sharktuner 6.3 shows the areas where O2-adjust is normally active (white) and disabled (red). The top rows are excluded, that is closed-throttle decel where fueling is irrelevant. Below 2800 RPM O2-adjust is always active (unless forced off by the WOT switch), and de-activated at higher load and RPM. The white area is the closed-loop “playground” where O2-adjust will always seek an AFR of 14.7, and the fuel map should be adjusted for 14.7.

Sharkplotter shows this clearly, closed-loop (O2-sensor active) is shown as small dots, and open-loop (O2-sensor disabled) is large dots. For the small-dot (closed-loop) areas the target AFR is 14.7, and for higher loads step the fuel up to 12.5 or whatever your preference is. And as noted, it is better to err on the side of rich once you get into the higher-load areas of the fuel maps.

By Shark