AFR Data Follow-up on Open/Closed-Loop Fueling Analysis



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AFR over TPS and RPM:

As a sanity check, I wanted to check my AFR values plotted as a function of TPS and RPM. I had about 2hr of data handy for this analysis. While this won't tell me whether the ECU is actually thinking it's in open or closed-loop mode, it will at least let me check the actual AFR for each cell. If the cell shows up as closed-loop in the previous map and then shows up as something wildly different than 14.7:1 on this map, then something could be amiss. Note that the converse is not necessarily true: if the cell was marked open-loop in the prior map, that doesn't mean that the AFR value can't be something close to 14.7:1; it just means that the ECU wasn't using O2 feedback to achieve that AFR.


This chart is a little messy, but you can see that it has the same general shape as the fuel trim data on the previous page. Note that the previous page's data used the TPS value from the OEM ECU; this data uses the actual voltage of the TPS signal, scaled similarly to the OEM values. Thus, the TPS values are very close, but not identical, between the two sets of charts. Of note is that even at WOT (95% throttle on the chart), the AFR still shows up around 14:1 below 2000RPM. This could be real, or it could be that if you punch it at 1500RPM, the RPM rises so rapidly that the AFR doesn't get read accuratly at that location.

Here's the standard deviation for the above chart.

Here's the number of data points for the above chart.




AFR over MAP and RPM:

Just for thoroughness' sake, I also plotted AFR as a function of MAP (boost) and RPM. This chart looks a lot cleaner, so you can probably infer that the ECU does AFR targets based on engine Load and not TPS (but we knew that anyway, right? ;-) )

Average AFR:

Standard Deviation of AFR:

Number of Data Points of AFR:



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Last Modified Sun Mar 02 2008 11:48:51 Pacific Daylight Time