Mass Air Flow Sensor adjustment? | FerrariChat

Mass Air Flow Sensor adjustment?

Discussion in 'Technical Q&A' started by ernie, Jun 5, 2004.

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  1. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,574
    The Brickyard
    Full Name:
    The Bad Guy
    I was reading the shop manual and it says that there is a CO adjustment screw on the MAFS. I recently took my car to get smogged and it just barely failed. It passed everything but the CO at 30mph. The max CO alowed @30mph is 6.0 and my was at 6.9. So it is just a hair off. According to the manual the CO can be adjusted by that screw. My question is which way do you turn the screw to lean out the CO? Also how to you balance the MAFS. I don't want to have one leaning things out too much and the other one making things too rich. I want these thing to be balanced. I looked in the archives and found how to balance the throttle bodies, but couldn't find anything on adjusting the MAFS. So I figure I would ask you guys for some guidance
     
  2. ShanB

    ShanB Formula Junior

    Jul 9, 2003
    547
    Tejas/Europe/Desert
    Full Name:
    shanb
    Hi Ernie. Glad to see you up an running again! How's it going bro?

    That screw is attached to a potentiometer on the MAFS which adjusts output voltage which indirectly affects mixture. I don't have the reference voltage offhand but basically I would adjust and "balance" the two by adjusting (with a multimeter ) to make the output voltage match the opposite MAFS at idle. Having said that - I doubt this needs adjustment at all as the ECU does a pretty good job of picking up small mixture variations and adjusting accordingly using the Lambda sensors. In my limited experience MAFS usually work or don't work and having to adjust one is pretty rare as there are no moving parts to wear out. Are you sure the problem couldn't be something else, like a vacuum leak or a bad 02 sensor?

    Shan
     
  3. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,574
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    Hey Shan

    For me things are good, for the car not so good. Just when you think you have this thing figured out it throws something else at you. But I will not be defeated by this car. At this point I'm not ruling anything out. I have checked the vacume hoses and they are all hooked up. Since this thing is only off by .9 it has to be something really small. Right now I wanna make sure that the MAFS aren't the problem. Then I'll hit the O2 sensors. Thanks for the advice. I was reading the shop manual and the voltage is to keep the heating wire at a constant temperature. Then as the resistance to this wire changes according to air flow it adjusts the fuel, in combination with the O2, crank position, and cam sensors. Other than that it doesn't tell you much. The manual is very vague. They didn't do a very good job writing them. I don't remember if it even said the amount of voltage that it used to get the wire to the needed temperature. So if you know what it is that would be of great help. Thanks again bro.
     
  4. ferrarioldman

    ferrarioldman Formula 3
    Professional Ferrari Technician

    Jun 19, 2002
    1,029
    Summerfield, NC
    Full Name:
    Tom Jones
    #4 ferrarioldman, Jun 7, 2004
    Last edited by a moderator: Sep 7, 2017
    6% sounds like a lot to me, like you might have some other problem. But if you want to check the adjustment on that air flow meter, see my attached picture. Take a resistance reading between the 2 indicated pins. It should read 383 ohms. Readings are usually within 3 ohms.
    Image Unavailable, Please Login
     
  5. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,574
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    Hey oldman,

    Thanks alot that is the info I needed, the picture is of great help too. Should I check it with the car running or off?
     
  6. jkuk

    jkuk Formula Junior

    Nov 3, 2003
    259
    Wirral, UK
    Full Name:
    John K
    Ernie,

    Try this website.

    It lists all Bosch sensors and gives specifications.

    A good learning site when trying to understand what these things actually do and what signals to look for.

    I used it to close down my crank sensor problems

    Cheers

    John

    http://www.boschautoparts.co.uk/mcSens1.asp?c=2&d=4
     
  7. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,574
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    Thanks John

    More great info. I will check the site out.
     
  8. ferrarioldman

    ferrarioldman Formula 3
    Professional Ferrari Technician

    Jun 19, 2002
    1,029
    Summerfield, NC
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    Tom Jones
    Ernie you have to check it with the car off. Just disconnect the plug and take your reading.
     
  9. fatbillybob

    fatbillybob Two Time F1 World Champ
    Consultant Owner

    Aug 10, 2002
    26,294
    socal
    Hi Ferrarioldman,

    Re: your ohm readings for the maf that number is correct as a starting point right? Or from your experience with 348's that has always been the number or FNA is lazy and always sets them to this number? Or?????All kinds of other engine parameters make up the final tailpipe CO and you remove that cap on the left of your picture and adjust from there while the car is running with a CO meter up the butt or better yet in the header CO sample ports. I'm not telling I'm asking. Is that right?
     
  10. ferrarioldman

    ferrarioldman Formula 3
    Professional Ferrari Technician

    Jun 19, 2002
    1,029
    Summerfield, NC
    Full Name:
    Tom Jones
    During a 348 school at FNA they told me this was the setting, period. If there was evidence of tampering we would know where to reset the adjustment back to. Those units cost too much to be fiddled with. A properly set up car drives very well and in my opinion these "extra" adjustments are not necessary. Your CO adjustment is automatic anyway so if you try to make any changes, the ECU is always going to try to compensate so that the reading at the O2 sensor is what it is suppose to be. If you try to make big adjustments, you may end up with an O2 sensor that is out of range and then you will end up with a check engine light.
     
  11. fatbillybob

    fatbillybob Two Time F1 World Champ
    Consultant Owner

    Aug 10, 2002
    26,294
    socal
    FOM,

    Thanks for the info. Ernie and I learned something today.


    Ernie,

    Are you O.K. with how to confirm the proper readings per FOM? I have the multimeter if you need one.

    FBB
     
  12. viperguy

    viperguy Rookie

    Feb 4, 2004
    22
    Hey ernie,
    I PM'D you. I am having the same problem with the engine missing around 5000 rpm's. I am also not passing emissions. Any info. would be great.
     
  13. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,574
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    The Bad Guy
    Billybob:

    I'll give you a call next week sometime to set up a date for us to get together.

    Viperguy:

    I got your pm and sent you a reply.
     

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