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Here’s a real long answer to your simple question,
Histograms are most effective when you are working on a parameter that is based on 2 variables, like VE which is based on RPM and intake manifold pressure.
Generally, the best way to set up your histograms is to see how the parameter table is loaded/plotted in the tune file. But MAF is a little different. MAF airflow is based on a single parameter......the frequency it measures. The higher the frequency the higher the flow.
If you look at AIRFLOW in your tune you will see a couple of plots of airflow vs. MAF frequency. One is for the low frequency range and the other is for the high frequency range. Theoretically speaking MAF frequency doesn't directly care about RPM or throttle setting or manifold pressure, only airflow rate, but in reality MAF frequency can get effected by the modifications you make to the engine. Thats why its the first thing you play with to get proper fuel air ratio when you've made upgrades to the motor. Provided of course that you are not running an SD tune.
If your fuel trims are showing that the ECM is adding fuel then you need to raise the MAF flow by that percentage at that MAF frequency. If the ECM is removing fuel then you need to lower MAF flow at that MAF frequency. I’m sure more experienced tuners have a better way but here’s what I did….
For NON-POWER ENRICHMENT CLOSED LOOP TUNING using the NARROWBAND O2 sensors:
This is usually for tweaking the low frequency MAF table…..Make a histogram which has dynamic airflow on one axis and MAF Frequency on the other axis. Then fill the histogram with LTFT’s or STFT’s if you’ve disabled LTFT. What you will get is a histogram with a diagonal line of data across the middle. Then read the histogram at a certain MAF frequency lets say 3100hz for example (which is near idle), what LTFT do you have in that box. If its +5% then you want to increase the flow in your tune file by 5% at that MAF frequency….if its say, -5% then you want to decrease the flow in your tune file by 5% at that MAF frequency…..is this making any sense? Like I said, I’m sure more experienced tuners have better ways to do it but this worked fine for me because I had plenty of time on my hands….I wasn’t on the clock….. LOL
For WOT POWER ENRICHMENT Tuning using the WIDEBAND O2 sensors:
This is usually for tweaking the high frequency MAF table …….also make a histogram which has dynamic airflow on one axis and MAF Frequency on the other axis but now fill it with LAMBDA instead of STFT. You want LAMBDA to be .90 (normally aspirated pump gas engines) when running in the power enrichment range. So now look at your LAMBDA’s in the histogram, if they are running .95 then you need to add 5% to airflow at that MAF frequency, if you have LAMBDA’s of .85 then you can take away 5% of airflow at that MAF frequency …….Is any of this still making sense????

See attached pictures.
Yeah that makes more sense. Not sure i need to monitor the MAF tune since its somewhat already dialed in but it wouldnt hurt to have the option to check it.

Hopefully i can get the wideband installed soon and just start with it vs using the narrowbands.
 
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