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MAF slope calibration

Practical Reflash Tuning

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Hi guys I am trying to calibrate my MAF scaling on a BMW F30 328i with N20 engine and MEDV17.2.4.

There are 3 MAF slope tables. I have them attached here. I made changes to only #1 because that seemed like the logical thing but my changes had no effect whatsoever. Any one want to chime in and help?

I was hesitant to change #2 and #3 because they have values of all 1 in them.

Attached Files

Those 3 tables don't appear to be for MAF scaling in the traditional sense, and likely are not what you're really looking for.

These appear to be compensations to airflow calculation, which have no impact in stock form if they are set to 1.0. These shouldn't be altered from 1.0 (no impact) until after MAF scaling has been performed, and then only alter these if you're sure the system really needs deviation from MAF derived air mass under certain conditions.

You'll likely need to adjust a traditional MAF scaling table. Usually it will be 2d with the axis being MAF voltage or frequency, and the z data being air mass flow, perhaps in grams/second, lbs per minute or similar.

Mike thanks for the insight, and yes I know what you're thinking coming from traditional reflashing but I've seen Andre speak about tables like these being used to alter the MAF scaling on Bosch MED controllers. If you look at the worked example you'd see he does this and there is no traditional 2D MAF curve like we're more accustomed to.

Anyone with specific knowledge on Bosch MED17 chime in?


Understood. When this is all you have available to you, rather than altering the MAF scaling itself, you're offsetting it with these tables, but both the process and end result are similar.

If you log % air vs. RPM and plot total fuel trim (long+short) as the Z data of a histogram, you can apply those corrections to the 2 tables you've pictured which have % air axes. For example if you have significant data points at steady state 3000 RPM, 90% air and your data shows -4% total fuel trim there, 0.96 correction, you can multiply the existing table value by 0.96 or perhaps just a few percent at a time i.e. 0.98, do the same for other RPM/% air areas where you have sufficient data. Try to keep the table data relatively smooth. Then retest in an iterative process until fuel trims a within a range acceptable to you.

As with any MAF scaling or fuel tuning, transients will tend to have larger trims, but as long as the engine responds crisply and cleanly to transitions, don't fret over brief significant trims in transients.

The RPM/Factor table with Z data all at 1 is separate and I wouldn't expect you to need to alter it.

Mike, I've already done exactly what you outlined above to table #1 and left the other two the same, my changes had zero effect. When I logged the car after I saw the same total trims which is what has me confused


I'm sorry I haven't got you closer to success just yet. I was also hoping someone with experience with that exact engine/ECU combo would chime in, but I'm doing what I can for now. The closest Bosch controllers I've tuned to what you're working with have tables like yours, plus the typical MAF scaling table, hence my earlier suggestion. I'd love if someone who has tuned that exact engine and controller with a big MAF housing could say for certain when the MAF is actively used on that platform, and how they accounted for a significant MAF related change.

Can you fill us in on the mods that you're trying to account for with tuning updates?

For now, in case you haven't already tried, as a general rule when determining if a table has any impact or not, I start with small changes as you likely have, to be safe. Then if no change is observed, I make a huge change just to be sure the table isn't having an impact. For example if you zero one of those tables out, start and drive the vehicle and observe no change, at least then you know for sure you'll have to find another way and can move on in another direction. Have you tried this yet to be absolutely certain the tables do nothing? Keep in mind some tables won't be active at all times, so adjustments may only impact certain operating conditions. I'm used to testing on a dyno where if the vehicle stalls upon entering a table which is zeroed out it's no big deal. If this won't be tested on a dyno, hopefully you have a big empty area to be safe.

Just to be certain, there are no other tables related to airflow available to you at this time?

What software are you using and if pertinent, where did you get the ROM definition i.e. DAMOS or map pack?


I appreciate the help thank you. I am using ECM titanium to make tuning changes. No other tables as far as I know to effect MAF changes. As to why I am wanting to adjust the MAF scaling, I am just being picky...right now my total trims are anywhere from -3% to -10% at cruise and WOT.

If you want I can send you the files and logs, send me an email address.

I love picky! Trying to optimize the system is what we hope everyone strives for.

It sounds like your trims are in pretty good shape, but using your knowledge to make them even better is a great goal to have.

For now I've left Andre a message in case he has some more specific info on your exact combo of software, engine, controller.

I've run this past James who helped with the course development. The issue is that ECM Titanium don't seem to have defined the actual MAF scaling table which is what you'd need to adjust. Unfortunately I don't know how much help we can offer since you're using ECM Titanium rather than OLS. The MAF scalar table is different in different controllers. Some are 1 x 500 while others are 16 x 40 so just providing you with an example of the table is not necessarily going to be useful. That being said, you shouldn't need to touch the MAF scaling if you haven't made changes to the intake system.

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