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  1. #1
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    Member No: 29126 Steve5and6 is an unknown quantity at this point Steve5and6's Avatar
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    Can the blow off valve spoof the AFM?

    If the AFM is mounted before the turbo, won't the blow off valve bleed off metered air? If so, won't the result be an over-rich condition? How is this best countered?

    Any advice greatly appreciated.

    Thanks...Steve.


  2. #2
    Joe
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    Re: Can the blow off valve spoof the AFM?

    If you are using the blow off valve to control the maximum pressure during exceleration, then yes you are venting metered air and therefore the ecm will be adding too much fuel.

    My understanding is the pop-off valve is to vent high pressure when the throttle is controled. You chould use a waste gate to control the upper pressure of a turbo system.

  3. #3
    Joe
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    Re: Can the blow off valve spoof the AFM?

    Mis-typing city.

    The pop-off valve is to control pressure when the throttle is closed, not while accelerating.

    There, is that better?

  4. #4
    ///ARINUTS...
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    Sort Of...

    What happens when you have a blow off valve that is after the AFM, evrytime you shift gears or let off the throttle, you get an extremly rich condition, since you are dumping metered air out of the system.

    The AFM subject is very debated here, check a few posts down.

  5. #5
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    Re: Can the blow off valve spoof the AFM?

    Run a tube/hose from the BOV output and Y it into the turbo inlet.

  6. #6
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    Re: Sort Of...

    In THEORY you should have an overly rich condition with a BOV, but the PCM strategy should prevent this from happening in any significant way. Typical strategy is to cut off the fuel injectors on throttle lift until the RPM's drop to some point (~1500 RPM). This is done for emissions and efficiency purposes. This strategy over-rides the AFM input which is essentially ignored during this brief period. Conveniently, this is when the BOV is venting, so the lost metered air doesn't matter.

    Since the BOV wasn't part of the factory calibration, I won't suggest that what I've stated above works perfectly under all conditions. It is possible that the BOV is still open when the AFM input gets proxied again, but at least the time period when it's blowing off the biggest volume of air is ignored.


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