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Thread: Crankcase vacuum; Unmetered air?

  1. #1
    Join Date
    Oct 2011
    Location
    Lexington, KY
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    527
    My Cars
    99 Coupe Hell Yeah Red

    Crankcase vacuum; Unmetered air?

    My Z3 coupe has a Vortech SC (6psi) and I have had MAF and O2 sensor codes ever since it has been installed. Car runs fine and the plugs look perfect. My question is: Since the crankcase positive pressure is pulled back into the pre-SC intake and after the MAF, does this mean that there might be enough un-metered air entering the intake after the MAF to cause error codes. Since the MAF is there to determine the amount of air intake, it seems that the air entering the intake after the MAF might confuse the system.
    I am getting rich codes for both banks and a MAF error code. I have replaced the MAF and sensors but the codes come back.
    ....or might it just be the tune? It seems that VF Engineering is not known for their wonderful tuning re-programs.

    Any thoughts?
    Is running a vacuum to the crankcase absolutely required? I know it helps but have seen many FI builds just venting the positive crankcase pressure to the atmosphere.

  2. #2
    Join Date
    Feb 2009
    Location
    Arizona
    Posts
    2,082
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    1998 e36
    Answer is simple, your MS41 is not tuned correctly. Also MAF does not like cone filter directly bolted on to it. It likes to see 6 inches of straight pipe in front of it for proper reading. Most of these FI kits are flawed in design

  3. #3
    Join Date
    Jan 2006
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    Oakhurst, CA
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    6,668
    My Cars
    96 M3 97 M3 98 M3 99 M3
    Takes some pics of how you have it setup before we let Hakentt talk you into a tune you don't need.

  4. #4
    Join Date
    Oct 2011
    Location
    Lexington, KY
    Posts
    527
    My Cars
    99 Coupe Hell Yeah Red
    Catch can pulls directly from valve cover (No CCV cyclone) and gets its vacuum from directly before the SC, after the MAF (hose connection shown). The filter is a bit further than 6 inches and the tube before the MAF is very slightly bent. I can easily get at least 6 in of straight pipe before the MAF with a small modification.
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    Last edited by Zoupe6; 05-29-2018 at 09:14 PM.

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