OK MAF fail set to 0 and I am going to log dynamic air and maf frequency.

So once I get a good log, I just want to set the maf table according to what I logged and thats it?

I assume that after I have dialed in the maf table for the first time and I want to test the maf, I just set the maf fail back to normal and go log AFR again?

 

Hey Chad, I guess you're gettin lucky on the tune not messin up, but hopefully this will help explain my experience. Based on an earlier VE discussion from many moons ago Nogo unveiled the VE equation

VE = ((massflow * IAT / (MAP * RPM * Displacement))

Now, all those little #s we see in the VE table are what's used for the left side of the equation when operating in SD mode, being that massflow is the only thing unknown (MAF offline). So we rearrange the equation and this is how dynamic airflow is formed. This would be the VE calculation of how much airflow to use when determining the fuel shot.

Massflow = (VE * MAP * RPM * Displacement) / IAT

Looking at the equation above, the variables seem to be MAP, RPM, and IAT. Supposing MAP and RPM stays constant, we can see that by variable IAT alone, air temp can certainly change the value of airmass, and thus also alter the calculated fuel shot. Now I don't know exactly what sort of AFR production this implies, but I do know that with more airflow, more fuel would be necessary to create an consistent stoich A/F burn right? I mean clearly, when the PCM sees more airmass as determined by the VE calc, it accordingly adds more fuel. Strangely, I originally tuned in 70 degree weather, but when 40s came around, I was producing 11.5-12.0 while commanding 13.0 in open loop/SD with no changes to the tune whatsoever. I logged this just to see why my car was driving like crap all of a sudden.

Whether or not the math model makes sense, it should also be assumed that the VE calculation of massflow is probably not always correct, due to some other external factors that none of us know about or have bothered to look into. That's the only reason why I would imagine my fueling getting screwed up with weather changes. I also believe this is why SD mode is ideal for situational use such as the track or on the dyno.

With the VE calculations we get variant massflow whereas with the MAF we get relatively stable and consistent airflow reported through a measurement device as opposed to mathematical prediction. This is why I believe that using your MAF, if calibrated correctly, will provide much more consistent fueling over a long period in a wide variety of climate.

 

Yes, from that point on you will want to reactivate closed loop, and MAF mode, and verify by reviewing your trimming, and WOT AFR. Chances are it will still need a little tweaking, my trims were indicating a bit rich down low and a bit lean up top after MAF recalibration, but for the most part, all other fueling was perfect. I then found certain frequency ranges where the fueling was a little off in my logs and adjusted accordingly. There were a few places I had to scale back or up a few % to get trims locked around zero. But as a whole, most of my MAF curve experienced about a 20-30% increase in airflow, which would distinctly go against the advice to just scale the whole maf curve up by 5%, 10%, etc. I think it's been proven enough by now that airflow is certainly not linear so to apply a constant multiplier throughout, while easier, may not be the most productive way.

 

OK wait a minute, I just logged my maf readings with everything set back to ON, such as closed loop, open loop F/A vs. Coolant Temp vs. MAP, and PE, with the only exception being that the maf fail was set to zero. So I need to log the maf readings while in pure VE open loop mode?

Then once I have the readings I can modify the maf table accordingly and then to test the whole system I will re-enable closed loop, re-enabled PE, and re-enable maf fail?

In the HPT tuning guide it doesnt mention what should be active and not active while scanning for airflow. But I guess it would make sense that closed loop shouldnt be active huh?

So just to verify....
1. Tune VE with closed loop disabled, PE disabled, and commanded AFR set to 13.0
2. Once VE is dialed in, leave everything disabled, but plug in MAF and run around logging airflow vs frequency.
3. Dial in airflow vs. frequency into the MAF table to match what was logged
4. Put everything back to ON and log
5. Go back to step 3 and re-adjust until you are happy.

Sound right?

 

After tuning your VE in open loop-SD, put all your tables back to stock pretty much, command whatever you want in PE mode, and reactivate closed loop. By zeroing the MAF fail frequency you will remain in SD mode, but have closed loop trimming and such and you will also be able to plug the MAF back in. It will still report data, but the PCM will ignore it. Either way it's that data in conjunction with VE data that will build your MAF curve.

Drive around for a bit to get your SD trims somewhat learned, then start logging for MAF recalibration. This is b/c now the only difference we have is b/w dynamic airflow, and MAF airflow. all other fueling functions will be held constant. If you want to recreate similar airflow of the VE calc, you want all the trimming to be present (even if minor) in SD mode in order to truly dial in a representative airflow curve for the MAF.

Once you've gotten your MAF building data, input the new table in, then reactivate MAF mode. You will probably notice some strange trimming here and there. Find the relative frequencies of your fueling problems and adjust accordingly. AS for WOT, keep the wideband on to verify that WOT airflow is providing a close AFR as to what is commanded. If not then also adjust accordingly. As said before the MAF recalibration is a starting point, not the say all end all airflow function.

I know it seems confusing, and it should! lol I tore my hair out awhile back trying to understand this so don't feel discouraged. It's not supposed to be easy I guess.

 

No, everything you say I understand, bc you actually take the time to give details. I will try what you said and then try using the MAF spreadhseet floating around here...and see if it gets me close.

 

This is an extremely informative thread for me! Thanks for all of the discussion and thorough explanations. I have all of the guides out there, but I have never been one to follow instructions with no understanding of what is going on behind the scenes. I have to know what is going on or it drives me crazy. As a new tuner, discussions like this are exactly what I'm looking for.