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348 MAF questions

Discussion in 'Technical Q&A' started by spider348, Mar 10, 2007.

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  1. spider348

    spider348 Formula 3

    Nov 3, 2003
    1,273
    MA
    Full Name:
    John
    #1 spider348, Mar 10, 2007
    Read the 348 MAF adjustment procedure as written on the 348 Owners site. Decided to check my MAFs while the 348 waits for spring. 1994 348 spider.
    Tubi exhaust, hyperflow cats. ECU's not connected.
    My meter automatically adjusts range. Right side reading off pins 1 and 6 was .394 K ohms, or 394 ohms if I recall. Not to far off the 383 recommended setting.
    The left side reading was 15 ohms! Difficult to access so I removed the airbox to insure proper connection. Reading was accurate. Removed the protection cap and adjusted the screw 5.5 turns CW to get a reading of .384 K ohms, or 384 ohms.
    Since I am dumber than a box of rocks when it comes to electronic systems built after the points/ condenser era I have some questions.
    How could the car run so well with the left side MAF so far out of tolerance?
    Will my adjustment adversely affect the car’s performance? Improve? What will the net result be? CO level? How could the MAF adjustment be that far out of spec?
    The car ran super, or so I thought. Passed Mass. Emissions testing.
    Recommendations and advice welcome. Very confused.
     
  2. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
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    #2 No Doubt, Mar 10, 2007
    When our Motronic 2.7 software sees a number wildly out of whack, it switches from the sensor value over to the stored (on our ECU chips) map value as programmed by the factory...using that stored value as a ballpark "guess" for what's right for your car.
     
  3. spider348

    spider348 Formula 3

    Nov 3, 2003
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    John
    #3 spider348, Mar 10, 2007
    Thank you No Doubt. I will adjust both MAFs to the factory recommended 383 ohm setting. Does the out of spec MAF have any fuel/ air ratio influence? My understanding is a low reading is rich, higher readings are lean. How does the Motronic ECU compensate? Trying to understand the relationship. I was under the impression an accurate ohm setting was required. Thank you again.
     
  4. ernie

    ernie Two Time F1 World Champ
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    Nov 19, 2001
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    The Bad Guy
    #4 ernie, Mar 10, 2007
    After you adjust both MAFS disconnect the battery, after a few seconds reconnect it, and let the car relearn the warm up parameters. Be sure to do this when the engine is cold, and don't touch anything, just let it sit and idle for about 15 minutes, then take it out for a nice long drive. That should do the trick.
     
  5. No Doubt

    No Doubt Seven Time F1 World Champ

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    #5 No Doubt, Mar 10, 2007

    Your MAF setting lets you adjust your A/F ratio about 20% plus or minus...but a wildly offscale (MAF setting) number will cause the Motronic software to ignore the MAF and use the stored factory guesses instead.
     
  6. ernie

    ernie Two Time F1 World Champ
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    #6 ernie, Mar 10, 2007
    The boy knows what he's talking about.
     
  7. gothspeed

    gothspeed F1 World Champ

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    #7 gothspeed, Mar 12, 2007
    Where does one tap in to get these readings??
     
  8. f355spider

    f355spider F1 World Champ
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    May 29, 2001
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    USA
    #8 f355spider, Mar 12, 2007
    Woudn't a reading that far off throw a Check Engine light?
     
  9. ferrarioldman

    ferrarioldman Formula 3
    Professional Ferrari Technician Silver Subscribed

    Jun 19, 2002
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    Tom Jones
    #9 ferrarioldman, Mar 12, 2007
    Last edited by a moderator: Sep 7, 2017
  10. spider348

    spider348 Formula 3

    Nov 3, 2003
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    #10 spider348, Mar 13, 2007
    Well then I screwed up! I referenced the 348 tech site. The recommended procedure is to check pin 1 to pin 6. Interested to know if there is any difference in my resistance readings based on ferrarioldman's recommendation. Thank you, John.
     
  11. F512M

    F512M Formula Junior

    Dec 9, 2003
    504
    Houston, TX
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    Jeremy Lawrence
    #11 F512M, Mar 13, 2007
    FWIW... I got the same readings from pins 1-5 and 1-6. 386 on the left side and 385 on the right side.


    JL
     
  12. No Doubt

    No Doubt Seven Time F1 World Champ

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    #12 No Doubt, Mar 13, 2007
    Pin 5 and Pin 6 will give the same reading vs Pin 1.
     
  13. spider348

    spider348 Formula 3

    Nov 3, 2003
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    #13 spider348, Mar 13, 2007
    No Doubt, thank you! If the weather here in NE holds, may be able to drive this weekend. Been a long winter!
     
  14. fana355france

    fana355france Formula Junior
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    Aug 10, 2005
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    nicolas
    #14 fana355france, Jun 8, 2007
    Do someone know the 355 MAF setting please ?
    Im still checking all electic sensors on my 355....
    thanks nico
     
  15. rimoore

    rimoore Formula 3

    Nov 18, 2004
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    Richard Moore
    #15 rimoore, Dec 29, 2007
    My MAFS were 3 high on one bank and 7 low on another to the 383 default. I set them both to 383 and will follow the cold reset procedure in the morning. Should I also go out and get a tester that measures the A/F ratio or just move on if the car runs fine.
     
  16. fatbillybob

    fatbillybob Two Time F1 World Champ
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    Aug 10, 2002
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    #16 fatbillybob, Dec 29, 2007
    So Gothernienodoubtvince....why not just leave the mafs off for the 348 hotrod project to lessen intake restrictions and just leave the motronic to default to basline maps or up the map via nodoubt tweeks and leave the map out of the loop?
     
  17. ernie

    ernie Two Time F1 World Champ
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    #17 ernie, Dec 29, 2007
    ^That^

    If it isn't broke don't fix it.

    But,

    If you wanna see what the O2 sensors are reading the sensor will come in handy.
     

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