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Thread: S-AFC tuning guide (

  1. #1

    Default S-AFC tuning guide (

    The following is a basic guide to tuning an Evolution VIII with a S-AFC/S-AFC II. Special thanks to Kyle (kpt4321) and our sister site, for providing the basis for this article.

    Setting up the car and S-AFC

    Before we begin the guide on how to tune with a S-AFC, you must make sure the car is set up correctly to do so. Make sure all the fuel components are in good condition, and make sure you have no boost or vacuum leaks.

    Make sure the S-AFC/S-AFC II is wired in properly;
    DO NOT do the "blue wire mod", it has been proven to degenerate the O2 sensor's signal.

    In the Th-Point section of the S-AFC, set the low trigger around 25%, and the high trigger around 65%.

    In the NePoint section, set them to;
    1k, 2k, 3k, 4k, 4.5k, 5k, 6k, and 7k,.

    S-AFC II (adjust your points where needed):
    1k, 2k, 2.6k, 3k, 3.6k, 4k, 4.6k, 5k, 5.6k, 6k, 6.6k, 7k

    Now, you want to use baseline corrections for fuel injectors. If you have the stock 560's, leave both tables at zero. Other starting points:

    660ís = -15% across, highs and lows
    680ís = -18% across, highs and lows
    720ís = -25% across, highs and lows
    750ís = -30% across, highs and lows
    780ís = -36% across, highs and lows

    If your ECU has been reflashed to run/accomidate larger injectors, leave the settings at 0% across, highs and lows.

    STEP 2: Fuel trims and low throttle

    Before proceeding past this point, you MUST have a logger of some sort!!

    Once you have the S-AFC all set up, start by setting the low throttle points, using the fuel trims. Doing this will require a basic knowledge of fuel trims;

    The ECU is, in essence, just a big set of spreadsheets (also known as "fuel maps"). It takes input from the MAS (in the form of Hz, temperature, and barometeric pressure) and comes up with a final value that represents the amount of air entering the engine. It also looks at the engine's RPM. With the RPM and an airflow value in mind, the ECU will look to the fuel tables, and find the amount of fuel it should inject into the motor.

    Then the O2 sensor comes into play. The O2 sensor tells the ECU what the a/f mixture looks like, if it is rich, lean, or right in the middle (stoich.). If the O2 sensor says that the mixture is lean, then the ECU will add a bit more fuel on top of what the tables tell it, until the O2 values get close to stoich. If it has to do this for a certain period of time, it will take note of that in the fuel trims.

    Evolution VIIIís only have 2 fuel trims, a long term fuel trim (LTFT) and a short term fuel trim (STFT). The STFT varies with the O2 sensor, an the LTFT goes for every rpm range. Since the STFT directly effects the LTFT, then you can just add the two together, and tune from there. For example, if the LTFT is +20%, and the STFT is -5%, you are at approximately +15%.

    Now, on to the tuning. Set up your logger to display RPM, STFT, and LTFT. Start the car and let it fully warm up. Leave it at idle, and we will begin to tune the low throttle table in the S-AFC.

    Now, look at the long term fuel trim. If it is positive, add a few percent on the S-AFC at the 1000 rpm point. This is not an exact science, but usually for about every 3 to 5% on the logger, you need 1% on the S-AFC. After adding or subtracting a few percent, let the car idle for a few minutes, and watch the fuel trims change. This may take a while.

    Continue to do this revving and holding the motor at 2k, and 3k rpm, or your designated RPMS 3.6k and under. After you are done and are fairly confident they are close, take the car for a drive and see if they change. Try to get the fuel trims close to 0% (+/-3). Remember, if the fuel trim is negative, you have to lean it out a bit, and if it's positive, you have to richen it up.

    Once they are at 0% (+/-3), and they have stayed that way for a drive, you can carry the numbers across up to 7k rpm. So, if you have -10% at 3k and 4k rpm, use -10% at 4.5k, 5k, 6k, and 7k. Then, you will also want to use -10% on your high throttle table, all the way across, until we begin to tune it in the next issue.

    STEP 3: Hi Throttle

    At this point you should have your fuel trims leveled out near 0% (+/-3), and that they have stayed like that for several days of driving. Also, this assumes that you have used the same correction factor that you used for the higher rpm's of the low table, all the way across the high table.

    Now, it's time to do some real tuning.

    Make sure you have your boost set where you want it.

    Now set up the logger. You want to make sure to log RPM, timing advance, and O2 (front), and throttle.

    Now, find a nice empty long road, turn on your logger, and make a pull in third gear. Make sure to go WIDE OPEN, really floor it, from 2.8k rpm to at least 6.8k.

    Now, save the log, and bring it up. Once you organize the data, it should look something like this (stock 04 Evo RS);

    RPM O2'S Timing TPS
    2585 0.83 20 100
    2753 0.87 7 100
    3175 0.89 1 100
    3664 0.89 5 100
    4234 0.89 7 100
    4718 0.91 8 100
    5156 0.93 8 100
    5550 0.93 9 100
    5875 0.93 14 100
    6171 0.93 15 100
    6460 0.93 18 100
    6738 0.95 20 100

    Look at timing and O2 values at all RPM values. Now you have to decide if, at a certain RPM, you are rich, lean, or just right. If you are too rich, your O2 values will probably be pretty high (over .98v) and you will have a decent timing advance. If you are too lean, then you will have less timing advance.

    You want to tune for timing advance and stable O2's. You want to keep the timing advancing nice and smooth and to peak at 19* (+/-2*) at 7k RPM. O2 values should also be flat across the whole RPM range with .92 to .94 volts, the ideal target range.

    So, with that information, decide if, for example the 3000 rpm point is rich, lean, or just right. Then, add or subtract just a couple % of correction, depending on your findings. You want to only do a few percent at a time.

    Then move on to the 4k rpm point, and do the same thing, looking at your data. Proceed with this up to 7k, and then make another pull with the logger to see the effects of your changes. This will get easier as you get more experienced, but it's not really that difficult.

    If you consistently sees 100% throttle during pulls, it no longer needs to be logged, just monitored, and this will give you a better sampling rate. If you are not seeing 100% when you should, your throttle sensor needs adjusting.

    Tuning: Advanced

    So, you have mastered the art of getting your fuel trims right at 0%, and you can make nice WOT pulls with a good timing advance. You've basically learned all that you need to know to have a car that runs well, but there is a little more to learn if you want run "really really well." This is where you will most benefit not just from this information, but from talking to others who have lots of tuning experience.

    Timing vs. Airflow

    Now, while the ECU has tables for the amount of fuel it needs to inject, it also has table for how much timing advance it should give you, and tables for how much it should advance timing depending on knock.

    For 0-3 counds of knock, the ECU will advance timing. For 4-7 or so counts, it will leave timing where it is, and anything over 7 will result in the ECU bringing the timing down in an attempt to control the detonation. While we cannot view this knock sum on a logger, it is there, you just have to interpret what it is by the behavior of the timing curve.

    Now, the timing tables in the ECU, just like the fuel maps, are indexed by airflow and rpm. With a S-AFC, this has an added effect. Since a SAFC intercepts that signal from the MAS to the ECU and modifies it, it can change the amount of airflow that the ECU "sees." If you have to correct your S-AFC into the positive range, than the ECU will see more airflow Hz than the MAF is outputting, and could change the timing map you are following. The problem with this is, higher airflow levels get less timing advance for safety, and lower airflow levels get more timing advance, because the ECU thinks you are pulling in less air.

    By leaning out the S-AFC (big injectors, more fuel pressure, race gas) you decrease the amount of airflow that the ECU sees, and therefore you will get a bit more timing advance for power. This all assumes you have no knock, and also keep in mind that more timing advance will have an engine a higher propensity to knock.

    Fuel Cut

    Another issue involving the amount of airflow the ECU sees, and the correction factors of the S-AFC, is fuel cut.

    For those of you who do not know, the ECU has a program that tells it to cut fuel when the airflow exceeds a certain amount. Now, this is with the final calculated airflow, not just the Hz signal, which means that temperature and barometeric pressure will effect fuel cut as well.

    If you are to install, say, 660cc/min injectors, you will be able to pull the correction factors within the S-AFC down about -10%, perhaps more. This means that the ECU will see about -10% less airflow under a given amount of boost than it would have with the stock setup, which makes it much less likely for you to get fuel cut.


  2. #2

    Default S-AFC tuning guide (

    here is more info

    MalibuJack from another thread..

    .. basically there are lo-throttle, hi-throttle, NE-Points, etc.. Its all documented but the docs aren't easy to follow.. MOST of the s-afc settings only address the high throttle points, and most have adjustments at 3000rpm and higher.. and for many of us, the high-throttle point is at 60%, though I've seen several with points higher than that.. and one or two with theirs set lower..

    Basically that 60% value means that your throttle position switch needs to read at 60% open before the S-AFC adjusts the max value of the MAF signal (Edit: The adjustment happens between the low-throttle and hi-throttle points, but the value is at its max at the high point - thanks Mark), keep in mind that with the evo, the 100% open TPS isn't really where your foot is planted to the floor, its somewhere around 2/3's to the floor.. thats why these values are important to set and pay attention to. it more or less reflects the point at which the car switches from closed loop operation to open loop maps.

    Any high-rpm setting (7000rpm or so) with 93 octane with more than -19% compensation is going to run extremely lean.. I wouldnt go more than 16% with 91 octane.. how you taper from 0% through that point is going to depend on your driving style and how your cars modifications respond..

    (EDIT: as mentioned in another post, I think it was determined that the point the engine goes from CLOSED loop operation, to open loop is approx 30% TPS reading.. This may or may not be accurate, I can verify this on a data logger at some point in the future)

    On a car with stock boost, you can actually lean it out a bit more than 19% if your running 94 octane, But I wouldn't attempt it until you can see what your actual mixture (With a wideband a/f) and egt's are..

    Oh, and just so you know.. just installing and initializing the S-AFC will result in a stock setting, its only when you adjust the lo-throttle or high-throttle compensation that it alters the MAF signal.. a positive value makes it richer, and a negative value makes it leaner.

    I wish I could give you step by step instructions, but I don't have the new S-AFCII to document it.. HOWEVER, the first two items to set are

    Low-Throttle at about 30-35%
    High-Throttle at (for most) 60%

    NE-Points can be set for 500 rpm increments through 7500rpm
    (2000,2500,3000,3500,4000,4500,5000,5500,6000,6500 ,7000,7500) I think that's 12 points..

    (Edit: NE-Points on the S-AFCII are at 200rpm increments, not 500)

    You can now take the values that you've seen here and map them as closely to an NE point in that list.. the points in between you can average the difference if needed.. any below the area you start compensating, around 3000 rpm, you can just leave at 0.. but don't leave any points between at 0...

    I hope this helps you translate the settings.

    If you plan on modifying the settings yourself after you have a baseline, I cannot begin to emphasize how important using a A/F Gauge (Wideband is better) and EGT probe.. You also need to have some form of performance benchmark to determine if what your doing is improving things, otherwise tuning it yourself is pointless.. We do this at the track pretty frequently..

    whe instaling the AFC.. READ the manual for the initial settings (karman, 4 cylinders..etc)

  3. #3

    Default S-AFC tuning guide (

    And here is the pin out..

    Power (red)----pin 25
    ground (brown)----pin 26 (closer to ECU)
    ground (black)-----pin 26 (away from ECU)
    RPM (green)-----pin 58
    TPS (grey)------pin 84
    Air flow signal out (pink)----pin 90 (closer to ECU)
    Air flow signal in (orange)------pin 90 (away from ECU)
    Knock sensor (purple)------pin 78

  4. #4

    Default S-AFC tuning guide (

    so where did all of this started from :lol:

    i think im gonna need a innovative ot zietronix wideband kit for this :twisted:

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