Put on bigger MAF and now running slightly leaner

Discussion in 'Fox 5.0 Mustang Tech' started by Black1987Stang, Aug 25, 2007.


  1. Black1987Stang

    Black1987Stang Active Member

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    I just took off my stock maf along with fenderwell Mac cai and replaced it with a Pro-M 75mm maf with just a filter on the end (it won't work with the CAI without making one of the pipes shorter) and now my air/fuel is around 13-13.3 on my wideband at WOT, with the stock maf and breathing though the fender it was around 12.4-12.9. Is that because the opening is so much bigger it's breathing in more air and thus a little leaner? (although the computer should richen it up a bit)(Btw I'm only running off one 02 sensor right now since the narrowband simulator isn't working)

    The meter was calibrated for 24's and I'm using the stock 19's But with the Tweecer I just uploaded the correct maf file and kept the injector slopes the same. I noticed the MAF voltage now is .6 but with the stock maf it was .8
    Is that normal? It runs and drives fine, can't even tell a difference actually :(
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Putting the air filter in the engine compartment is bad practice. The engine compartment turbulent air and heat do odd things to the airflow though the MAF. That upset in airflow through the MAF changes the air/fuel ratio.
  3. patrickmx2

    patrickmx2 New Member

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    "13-13.3 on my wideband at WOT, with the stock maf and breathing though the fender it was around 12.4-12.9. Is that because the opening is so much bigger it's breathing in more air and thus a little leaner?"

    With no other changes, this suggests you are possibly flowing less air "across the sensor". The MAF is used in LOAD calculations. So less air means less LOAD. So you are accessing a lower row in the OL fuel table which is probably a leaner number.

    You may be flowing more actual air but the sensor is only seeing so much of it. Considering you also changed the MAF curve you could have just caused that yourself. If you put in a lower KG value in at the same voltages it tells the EEC you are under less LOAD.

    If you are logging the SAME voltage, or LOWER voltage this would bring on more discussion. Forget the KG at the moment, what MAF VOLTAGE are you seeing at WOT? A higher voltage suggests more airflow and that is expected you just have to make sure that voltage represents more air instead of less. The eec takes the voltages and then looks at the transfer to see how much air "you" say is flowing at that voltage, because "you" are in charge of the transfer data via the Tweecer.
  4. 2002BLGT

    2002BLGT Well-Known Member

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    try scaling your whole MAF transfer function up by 5 percent and see what happens .....
  5. vristang

    vristang Advanced Member

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    That should put you pretty close...

    13/12.4 = 1.048
    A rough change of 5%
  6. loud 95

    loud 95 New Member

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    As a bit of a side note, I was wondering if you had the Maf transfer function available for your Maf? I have the same maf and 24lb/hr injectors, but do not have the maf transfer function. Could you send it to me?
  7. ninety15.0

    ninety15.0 New Member

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    I am also looking for the MAF data sheet for the 75mm bullet cal'd to 24# injectors. Do you know if yours was calibrated for the stock airbox or for a cold air kit? Pro-m cal'd their meters differently depending on the intake tract. If you have this sheet would you mind PMing me about it?! Thanks in advance.
  8. Black1987Stang

    Black1987Stang Active Member

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    I'm not sure if it was calibrated for cold air intake or stock cold air kit but doesn't matter in my case since all I used was the "PROM_24" file that came in CALEDIT for my Tweecer R/T. I'm not sure how to send the file through mail so if you let me know how to send the file I have no prob sending it to anyone.
  9. Black1987Stang

    Black1987Stang Active Member

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    Now that I think about it I'm not sure if you'll be able to use what's in the files since I'm running 19's with it? With the Tweecer I just kept the injector slopes stock (for the 19's) and just uploaded the PROM_24 file...maybe I should have loaded the PROM_19 file instead anyways? I don't know...but if you need anything I got I have no prob sending it.
  10. vristang

    vristang Advanced Member

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    The PROM_24 file should be used when your MAF meter was 'calibrated' for 24's.
    You should use the PROM_19 file if your MAF meter was 'calibrated' for 19's.
    It should say right on the meter, what it was calibrated for.

    When you have the tweecer you have no concern for whether the MAF 'calibration' matches the injector size...
    You just need to get the MAF Transfer to match the MAF meter...

    For a while I ran a 19Lb MAF calibration on my X3Z with 30Lb injectors.
    When changing the MAF meter, you only need to change the MAF Transfer setting.

    jason
  11. Black1987Stang

    Black1987Stang Active Member

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    I gotcha....thanks for clearing that up Vristang

    If anybody can use it just ask

    Sean

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