MAF conversion made simple

[SVOeric]

It's been brough up several times. This is a Doc I found on Chris Roth's site. I take no credit for it, and would like to thank the author
(I believe it is Mark Proctor)

MAF Conversion Made Simple for P-Series Processors

Purpose Statement: The purpose of this project is to adapt a MAF meter to use on the 2.3T processor strategy in as simple a manner as possible using PCMX and an EEC-Tuner. I want to leave the stock fuel equation unaltered, but work around it as a means of implementing the MAF in lieu of the VAM. This rationale allows one to leave as much as possible unchanged, and (I believe) is infinitely more understandable for the novice tuner. I also want to change the stock airflow “cap” of 32 lbs/min, and use flow values that are best suited for the 2.3T EEC. I will assume those using this document possess a basic understanding of the 2.3T EEC’s fuel strategy, and are reasonably comfortable working with PCMX. If you need to learn more about the fuel strategy, first read SAE paper #840251 (“Turbocharging the 1983½-1984 Ford 2.3L OHC Engine” by Dertian and Hutchison) that’s in the tuner23 archives and then peruse my EEC fuel equations document. If you need to learn more about using PCMX, read through Kevin Timmerman’s user’s guide on the PCMX website (http://www.pcmx.net/pcmx/guide). The principle elements you’ll need to adjust via PCMX are as follows:
· P_0404—Mass Air Flow Multiplier
· P_0408—VAF Sampling Average at Idle
· P_0520—VAF Low Limit
· P_0522—VAF High Limit
· P_1E08—Minimum VAF
· F_0A58—Max VAF vs. RPM
· F_0ED6—VAM (or for the current purposes “MAF”) Transfer Function
· F_0FEE—Air Mass Transfer Function
· Hex Locations 0x2312 and 0x2313—MAF Cap
Those wishing to do the swap will also need the following hardware and data:
· A mass airflow sensor that works on a 5V scale.
· A detailed flow (preferably in lbs/min) vs. voltage map for the meter in question. I would think any really useable flow sheet would contain at least 20-25 data points. Pro-M has 48-point flow sheets for their meters listed on their website.
· A VAT sensor that has been extracted from a junk VAM for use as an IAT. There’s been a lot of talk about adapting a later model IAT or ACT for use on our cars, but until someone perfects that swap I’ll just advise you to stick with what we all know works. Hopefully I’ll be able to amend this sentence before too terribly long. After all, the VAT is an ugly and fragile little booger and it’s somewhat difficult to secure to the intake tract.
In all of the following calculations, I will round as little as possible until PCMX yields a “hard” number for me to work with. I think this is the most accurate way to do things using the tools at our disposal. Since John Baas has done an adequate job of describing the physical installation of a MAF sensor on one of our cars, I will not rehash that information in this document. My thanks go out to all those who have contributed to the MAF conversion thread over the past two years or so of the list’s existence. If it weren’t for the archives and some private pieces of correspondence, this document would have been impossible to compile. I might also say that I consider this a “work-in-progress,” and hope you all will peruse it with an eye towards its perfection (i.e., any and all feedback is welcome).

Air Mass Transfer Value: The “Y” column numbers in the Air Mass Transfer function (F_0FEE) represent the values derived from the following equation in the 2.3T EEC’s fuel strategy:
AMT=
Actually, the “Y” column values are just the square roots of the corresponding “X” column values. BAP and VAT values are derived from sensor inputs. Once the EEC determines the appropriate AMT value for current weather conditions, it uses a second equation to calculate metered air mass:
AMVAL (Air Metered Value)=Lbs/Min=CFM*.3187*AMT
The EEC uses the VAM to determine cfm value, and .3187 is a correction factor for Ford standard temperature and pressure (see P_05EC). Since a MAF provides a direct measurement of air mass, those wishing to convert from VAM to MAF need to bypass the AMT calculation step in the fuel equation. In order to do this, you’ll have to select a set value for all of the “Y” column values in F_0FEE. I prefer .25 since it is a nice “round” number in PCMX, and more importantly because it is a half-scale value (i.e., the acceptable range in F_0FEE is 0-.5). Making all of F_0FEE’s “Y” column values the same makes it impossible for variations in barometric pressure and ambient temperature to affect the EEC’s AMVAL calculation via the BAP and VAT sensor inputs. You’ll be leaving that task up to the MAF from now on.

Resultant AMVAL at 256 CFM of Airflow: 20.396484375 lbs/min. I arrived at this number by using the AMVAL equation and the corresponding “long” values in PCMX:
AMVAL=Lbs/Min=CFM*.3187*AMT=256*.318695068359375*.25
256 cfm is a good starting point for our calculations is because it is a nice “round” number in PCMX and because it is a half-scale value (the acceptable numeric range in F_0ED6 is 0-512). We will use this number to help scale the “Y” column values of the VAM transfer function so that they accurately represent flow in lbs/min.
Finding the Best Scalar for “Y” Column in VAM Transfer Function: Since we’ll be using 256 cfm as our starting point for finding the correct scalar for F_0ED6, and since none of the “stock” “Y” column values are exactly 256, you’ll need to change the final cfm entry from 361 to 256 for testing purposes. Once this is done, simply edit F_0ED6 by changing the “Y” column scalar value until the final “Y” column value is as close to 20.396484375 as possible. What you’ll find is that whenever the “Y” column scalar for F_0ED6 is set to 1606.5, the function’s airflow values most closely approximate the correct lbs/min values whenever AMT remains “fixed” at .25 and at the rest of the fuel equation (i.e., P_05EC) remains unchanged. However, since we will be using a P_0404 value of 2 (actually 1.99996948242188) in order to get around the initial MAF clip, we’ll need to halve the “proper” scaling value to 803.25. Using this scalar value allows the tuner to enter the flow rates from his or her MAF flow sheet into the “Y” column of F_0ED6 in terms of lbs/min.

[SVOeric]

Best Mass Air Flow Multiplier Value (P_0404): 1.99996948242188. This is the maximum value that PCMX will allow you to enter. Using this multiplier value helps the tuner “work around” a max air flow clip of 32 lbs/min, upping it instead to 64 lbs/min.
Changing the MAF Sampling Average at Idle: Changing the value in P_0408 from 1 to 3 can help improve idle quality.
Changing the VAF Low and High Limits: Because the VAM produces a voltage signal KOEO, the stock P-series code sets a VAF low limit of .1709V at P_0520 and a minimum VAF signal of .2179 at P_1E08. Since the MAF sensor does not produce any signal voltage unless the motor is running, you’ll want to change both of these values to 0. Also, since most MAF meters are on a 5V scale, you’ll probably want to bump the value of P_0522 a bit higher than 4.5 V. I set mine to 4.8V.
Adjusting F_0A58 to Accept Higher Voltage Signals: Since most MAF meters are on a 5V scale, you’ll probably want to bump some of the “Y” column values in the Max VAF vs. RPM function to allow for higher readings. I changed all values >3000 rpm to 4.6V.
Expanding the MAF Transfer Function to Include More Data Entry Points: Some consider this to be an unnecessary step in the conversion process, and to an extent it is. Since the “stock” VAM transfer table only contains 25 rows, I worry that I’ll lose a fair amount of meter resonance by shrinking a 48-point flow sheet to fit a 25-point table. There is, however, a fairly simple fix we can use to enlarge F_0ED6 to contain 32 or even 36 rows. This task requires a modicum of familiarity with using the hex editor in PCMX. Since the functions F_0EAA, F_0E9E, and F_0E92 aren’t really utilized in the P-series strategy, we can all feel comfortable shrinking them for the sake of expanding F_0ED6 into their territory.
· Thankfully, there is only one place in the P-series code that “calls out” the table address for the MAF transfer function, and its hex location is 0x1E8E. Once you expand the MAF transfer function, you’ll want to change this hex value from 2ED6 (the normal starting point for the VAM transfer function) to either 2EBA (for the 32-point table) or 2EAA (for the 36-point table).
· Point-by-point directions for building a 32-point table:
o Step #1—Edit F_0ED6 by changing the function size to 32.
o Step #2—Edit F_0ED6 by changing the “X” axis address to 0x0EBA.
o Step #2—Edit F_0ED6 by changing the “Y” axis address to 0x0EBC.
o Step #3—Edit F_0ED6 by changing the “Y” axis units to Lbs/Min.
o Step #4—Edit F_0ED6 by changing the “Y” axis format to %5.2f.
o Step #5—Edit F_0ED6 by changing the “Y” axis max to 33.
o Step #6—If you like you can change the VAM transfer function’s name to reflect it’s new purpose and location (i.e., 0EBA MAF Transfer).
o Step #7—Enter your 32 data points into your newly created MAF transfer function.
o Step #8—Change hex location 0x1E8E from D6 to BA.
o Step #9—Rename and save the .bin and .rdt files.
· Point-by-point directions for building a 36-point table: Constructing a 36-point table is a bit more involved since it requires emendations to four functions instead of one.
o Step #1—Edit F_0ED6 by changing the function size to 36.
o Step #2—Edit F_0ED6 by changing the “X” axis address to 0x0EAA.
o Step #2—Edit F_0ED6 by changing the “Y” axis address to 0x0EAC.
o Step #3—Edit F_0ED6 by changing the “Y” axis units to Lbs/Min.
o Step #4—Edit F_0ED6 by changing the “Y” axis format to %5.2f.
o Step #5—Edit F_0ED6 by changing the “Y” axis max to 33.
o Step #6—If you like you can change the VAM transfer function’s name to reflect it’s new purpose and location (i.e., 0EAA MAF Transfer).
o Step #7—Enter your 36 data points into your newly created MAF transfer function.
o Step #8—Change hex location 0x1E8E from D6 to AA.
o Step #9—Edit F_0EAA by changing its size to 4.
o Step #10—Edit F_0EAA by changing its “X” axis address to 0x0E9A.
o Step #11—Edit F_0EAA by changing its “Y” axis address to 0x0E9C.
o Step #12—Change the function’s name to reflect its new location (i.e., 0E9A Load [TRI for M_08A5 KAM]).
o Step #13—Enter the values that were in rows 8-11 of F_0EAA in the stock file into rows 1-4 of the new function.
o Step #14—Edit F_0E9E by changing its size to 2.
o Step #15—Edit F_0E9E by changing its “X” axis address to 0x0E96.
o Step #16—Edit F_0E9E by changing its “Y” axis address to 0x0E97.
o Step #17—Change the function’s name to reflect its new location (i.e., 0E96 KAM spark advance gain)
o Step #18—Enter the values that were in rows 5-6 of F_0E9E in the stock file into rows 1-2 of the new function.
o Step #19—Edit F_0E92 by changing its size to 2.
o Step #20—Rename and save the .bin file and .rdt files.
Upping the Max Air Flow Limit to 64 lbs/min: Change hex location 0x2312 from 01 to FF. Change hex location 0x2313 from 3A to FF. This change is necessary for those of us whose motors move more than 32 lbs/min worth of air.