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Old 04-29-2009, 10:53 PM   #1
nsceviour
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Maf Transfer Function tuning.

This is a process i use that i've been using since 2004. Hasnt failed me yet. im basing this on using SCT Advantage tuning software, and live link datalogging software, with a LM1 wideband, but you can datalog with various handhelds,programs.

First you set the correct AFR at idle. Just data log for a minute after it's warmed
Then only look at MAF counts and short_term fuel trims (the one that's actually changing) you want to see that value at 1. If the value is below one, you're actually lean.

Let's say it is 0.8 (so you're 20%) lean so what you do is you go to the maf_transfer_function and look up the value for the maf_counts that you were reading while idling (probably around 100) and you multiply it by 1.20 (adding 20%) then you do no-load tuning, again, warm up the car and while data logging, slowly rev up the car through the rpm range while looking at your MAF counts, don't let them go over 500. (Now, by slowly, I mean don't let it increase by more than 100rpm in a second)

In closed loop you don’t want over 500 counts.

So it should take you close to a minute to go through RPMS, from 0 to your last rpm before redline

Now, if you at any point see the fuel_trims completely out of whack, stop
but, if you go through this, and you see that your fuel trims are, let's say too rich throughout the band by maybe 10%, that means, short term fuel trims = 1.10. Even though you only reached maybe 400 MAF counts, I would multiply the entire MAF count range all the way up to 1023 by 0.9. (Drop 10%)
If it's rich by 10% up to 400 it's most likely rich by that much further up. So you repeat this until you’re within 2-3% on either side of the fuel trims.

0.97 - 1.03 should be the range you're shooting for
Depending on skill it can take 3-4 runs

Now since your fuel trims are already close, this should be easy. Basically, when you're driving you'll reach 450-500 counts real fast. So you want go maybe in 2nd gear and very slowly start accelerating

*your girlfriend or car buddy with a laptop in they’re lap would help here.

So basically just tell them to yell at you when the car hits 500 counts
Then start over
Never look at data in the range where you're letting off gas its useless data there. Only when accelerating. So drive around for a few minutes, pull over, update and so on until you're within same range again (may take 2-3 runs)
*Don't data log too much for each run cause you'll go crazy looking over all the data*

Ok, once you're happy with the trims, you do W/OT runs

*Note save every single copy of your file as you update it, never know you may make a bad change*

First, you can do a 2nd gear pull all the way to redline and just get data off your wideband

So you take that data and use it to adjust the upper part of your MAF function basically in the same way you adjusted the lower part. Except now you calculate the number you multiply by a bit differently.

So from 500 up you take the AFR that you are reading from the wideband, let's say 13.0 and divide it by the number you're commanding in your fuel table, let's say 12.0.

So you get 13.0 / 12.0 = 1.083

Multiply a given cell for a given MAF counts by 1.083
you do this for every cell you can reach, after every change, make sure to double check the graph for the transfer function to check that it's at least somewhat smooth.

*Don’t Peg your MAF*

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Last edited by nsceviour; 04-29-2009 at 11:01 PM.
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