MAF Calibration 101

[jdeves]

Thanks so much for the write up and the excel sheet it made is soooo simple to calibrate my maf! I just finished an install of an atp 3071 turbo/fmic and using your instructions I was able to get my closed loop fuel trims perfect in just a couple hours. Now on to the open loop!

[Steve @ VersaTune]

Glad it helped!

[maestro]

... add the STFT and LTFT to get the combined fuel trim. Record the combined fuel trim on the calibration spreadsheet next to the corresponding MAF voltage. Do this at as many data points as possible throughout the MAF voltage range where LTFT and STFT are non-zero. The worksheet will calculate the multiplier to apply the cells of the MAF Calibration tables in Tune Editor.

Howdy - I'm just trying to do my MAF calibration now ... but since VT logs STFT1 and STFT2 - which did you mean in the above sentences? Or do I simply add together all three fuel trims to get my error?

[Steve @ VersaTune]

STFT B1S2 is the narrow band sensor trim. It has very little control over the trims and is only used at light load when target afr is 1.000 lambda.

You can include it if you want, but it doesn't make much difference either way.

[maestro]

Hokay - thanks Steve

Also, one other oddity I've noticed. I've managed to get my LTFT to read zero on very small throttle inputs all the way to the redline ... however, if I then choose a higher gear and find the same MAF voltage and engage cruise control, I get a different reading.

For example, accelerating very, very gently in second gear to capture a wide band of MAF Vs will pass through, say, 2V and it'll do it at 0% LTFT but if I'm in 6th gear at a MAF V of 2V and on cruise control then I might be seeing something like -14% LTFT Wassthatallabout?

I've just been out and done it in various gear and constant speed at constant Maf V gives me negetive LTFT whereas the slightest bit of acceleration gives me 0%. Whih reading should I be using to calibrate the closed loop system?

[Steve @ VersaTune]

Try to log at steady state. Steady throttle and MAF volts. To get the higher voltages, use higher gears. I sometimes use 6th gear and the hand brake to get high MAF volts and minimal acceleration.

[maestro]

OK cheers - steady state it is then

And does this AFR thingimabob for the open loop have to be so laborious? OMG my eyes! I'm working on the assumptiong that I'm filling in the gaps between readings. Obviously WOT runs don't last long by their very nature and so there's a lot of gaps in the data to enter in the spreadsheet. I guess we just manually smooth the data through those gaps?

[skiptownmcat]

OK cheers - steady state it is then

And does this AFR thingimabob for the open loop have to be so laborious? OMG my eyes! I'm working on the assumptiong that I'm filling in the gaps between readings. Obviously WOT runs don't last long by their very nature and so there's a lot of gaps in the data to enter in the spreadsheet. I guess we just manually smooth the data through those gaps?

You can do a bit of "smoothing" I think it's just easier to enter every voltage point though.

[Steve @ VersaTune]

The spreadsheet has been updated to fix an error in the OL multiplier calculation.
Thanks to YuraL for pointing out the error.

[skiptownmcat]

The spreadsheet has been updated to fix an error in the OL multiplier calculation.
Thanks to YuraL for pointing out the error.

What was the problem Steve?