• Warning !! Before you change that tune read this!

    Danger don’t change that tune until you read this!

    Due to the fact that many Mustang owners are modifying their cars today to the point of taking the HP, fuel and timing demands well past the stock calibrations many of these cars now require professional tuning.

    The problem the Mustang community is facing is finding a tuner who knows and understands how to tune a mass air car properly and does it the way FMCO does it.

    Unfortunately for the community today outside of Ford Racing and those who work closely with Ford Racing there are very few tuners if any out there that do tune correctly which is why I felt it necessary to post this warning to all!


    MAF basics By Jim LaRocca

    Some basic info about MAF and MAF transfer curves.

    Understanding a mass air meter and why it so critical to have the correct meter curve in a tune.

    This is where 99 percent of the tuners get themselves in trouble and it all starts from step one.(The Mass Air Meter and Meter Curve) Lets not even worry about the rest of the tune (that's a completely different story)the first and most important step all starts here.

    The MAF meter is the first point where air enters the motor and every calculation and I mean every calculation the computer does will depend on that being a actual and real measurement. (Load, Idle,part throttle, WOT, A/F, timing, torque calculations ,etc. all depend on it)

    The main purpose of a Mass air meter is to measure airflow.
    The Meter operates in a range from 0-5volts
    5 volts being the highest it could read

    Every voltage point from 0-5volts for a given mass air meter and sensor represents an actual air flow measurement.

    So if you put a MAF meter housing with a sensor on a flow bench you can obtain a mass air transfer function for that given meter sensor combo.(A mass air meter will only work correctly/measure correctly if these values are accurate)
    So lets say this is the data you obtained after flowing the meter on a flow bench.(And by the way this is exactly how Ford does their mass air meters and curves)

    0 volts = 0 airflow
    1 volt = 500 CFM
    2 volts =800CFm
    3 Volts =1200 cfm
    4 volts = 1500 cfm
    5 volts =1800CFM
    every voltage point in-between those valves will also equal a CFM valve somewhere between them .(Just using whole numbers for this example.)

    If you needed A MAF meter to measure more CFM, there is two ways to do it correctly.
    One use a different sensor that has a different range in the same housing.
    Two use the same sensor but increase the size of the housing

    Another note since CFM is a direct relation to HP this is how a computer can/will calculate the torque the motor is making at a given RPM.(one way how torque management works/is calculated)

    It takes 1.5 CFM to make 1 hp

    Knowing this, you can take a mass air voltage/reading from your MAF and calculate how much HP your engine is making.(But again only if you know the meter and meter curve is accurate)
    Believe it or not this is how top fuel teams figure out how much HP their engines make(Hard to dyno an engine making 5000hp plus HP, no dyno can really read that high, until maybe the last couple of years) They measure how much CFM the engine is moving and then calculated that into HP

    Now going back to one of my first statement's that 99 percent of the tuners get themselves in trouble here and cause all kinds of issues ranging from bad startups, pinging, driveabilty issues, idle issues etc.
    Here is why

    Most tuners out there were TAUGHT.... to adjust the A/F ratio by moving the transfer curve in the tune. (Will it change an A/F ratio it sure will...........) They really don't understand how a mass air system works. (If they did they would NEVER do this) Its really a shame because most tuners feel this is the correct way to tune.(they really believe they are tuning correctly)
    Why ... again because this is the way they were shown. Since they were shown that, it has to be correct way. They were never actually shown or understand what that mass air meter is doing or suppose to do.

    They were also taught to create a mass air curve from scratch or adjust a curve by datalogging short terms or using an A/F gauge to tweak or enter a value in the curve depending on the short term voltage or the a/f ratio measured coming out the tailpipe.
    They will move a curve up or down until they get the a/f ratio they are looking to obtain.

    So lets see why this is the wrong way of doing things
    Lets look at the example data above created from a MAF metering using a flow bench.

    Lets take the 2 volt measurement which equals 800 CFM (which we know is a real and actual air flow measurement for this example)

    We are driving our car and the mass air meter is at 2 volts.
    OK the computer will take that 2 volts reading and start calculating how much to open the injector to hit a target A/F, referencing the air fuel ratio target map. (If the injector slopes and all are correct in the tune and depending on your fuel pumps/system etc. whatever you have in your target a/f will be what you will obtain out the tailpipe)

    It will also look/calculate load, timing maps etc. from this measurement but lets just look at the A/F ratio here.

    If for some reason (and can be many) the target a/f is suppose to be 12 to1 and 10 to 1 is coming out the tailpipe.

    What the tuner will do instead of adjusting the correct parameters is they will take the 800 CFM value at 2 volts and make it a smaller CFM value/ number in the maf curve to trick the engine in thinking its moving less air.
    If the engine thinks its moving less air it will calculate the injector not to open as much delivering less fuel, which will cause that 10.1 A/F to hit the 12.1 A/f that is targeted.

    So what they do and how they tune, is by looking at or only caring only about the A/F ratio.
    Every other calculation done at that point by the computer will be wrong..... why ....................because it is thinking it is moving less air than it really is now!!!! This could potentially be very detrimental to the engine and even lead to catastrophic engine failure especially on highly modified engines.
    This is a real basic and simple example.
    I hope this helps your understanding of why and how important it is to really know what that mass air meter is measuring and what the MAF curve does in the tune.

    A few years ago it was more forgiving when the drive by wire didn't exist to tune by moving or creating a MAF curve the wrong way.

    Drive by wire and or highly modified cars will only amplify issues when a car is tuned with an inaccurate MAF or MAF curve.

    There are many more other unintended negative affects that will occur as a result of a tuner who changes a known MAF curve that has been established on a professional flow bench,( like the one Ford uses) for the purpose of adjusting air/fuel but I’ll leave that for another day.

    Some interesting reading here about tuning and Maf calibration.
    Ford Racing parts catalog ….Read page 154 bottom paragraph

    page 220 explains a little about the maf and its calibration

    This article was originally published in forum thread: Warning !! Before you change that tune read this! started by Birdman View original post