Questions on TFI

Discussion in 'Engine, Fuel and Exhaust' started by slimjim47, Apr 6, 2009.

  1. slimjim47

    slimjim47 Member

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    1) What exactly does the O2 bypass do?

    2) How is the idle mixture adjusted independently from cruising RPM's?

    3) They make claims of the fuel metering being accomplished by load rather than RPM's. Can someone explain exactly how the load is determined or sensed.

    I'm sure I'll have more questions so bear with me.

    Thanks...Jim
     
  2. glider

    glider Veteran Member

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    The 02 bypass removes the 02 sensors from the system unless you get the one that keeps them which kind of defeats the purpose of the unit.

    The idle mixture is adjusted with the #1 pot and the #3 pot is for cruising. There's much more info in the self help forum on the TFI.

    I believe you are referring to the function of the throttle body and the TPS and the MAP sensor here. It adjusts the ECM which in turn adjusts the TFI also.
     
  3. harley@16

    harley@16 Junior Member

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    My question is when the o2 sensor is by-passed, does the bike run open loop? If so isn't the mixture 12:1? The sensor would have to be sending a reading to the ECM for the EFI to function closed. So does the bypass give a false reading to the ECM in order to accomplish this?
     
  4. harley@16

    harley@16 Junior Member

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    I just put mine on last weekend and took a couple of short rides and it's amazing how diff. a little more fuel makes. I set it rather conservative and still the bike has a whole diff feel. More throttle response, smoother running at all rpms, even some diff in the muffler tone. I love it. Thanks HD Talking for all the great info. Glider, Hobbit, Smitty, and all the moderators, you are a great help to all of us.
     
  5. Bud White

    Bud White Well-Known Member Retired Moderators

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    it runs in open loop the pots are what your using to basically set the mixture
     
  6. harley@16

    harley@16 Junior Member

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    Another query, when a sensor is disconnected or otherwise not functioning, doesn't it set a code in the ECM thus activating a check engine lite? If so how does the by-pass defeat this function?
     
  7. Bud White

    Bud White Well-Known Member Retired Moderators

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    bypass keeps it from setting codes
     
  8. harley@16

    harley@16 Junior Member

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    I did a little searching on the doebeck site and found a forum that discusses all questions about the TFI and one thread explained the o2 sensor by-pass as having a resistor in it. This would probably allow the ECM to run closed loop giving the starting value of fuel ratio at the stock setting of 14:1.See EFI - Electronic Fuel Injection Controllers - Motorcycle, ATV, Snowmobile, UTV
     
  9. glider

    glider Veteran Member

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    That's correct about the resister. It's a small unit that plugs into the end of the wire where the 02 sensor usually plugs into about 6" upstream of the 02 sensor itself.

    I like to run the TFI without the 02 sensors for better control of the AFR to where I want it.
     
  10. slimjim47

    slimjim47 Member

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    What makes you say it runs in open loop when the O2 sensors are bypassed?

    This is where the TFI site doesn't explain much. What AFR are you referring to when you say " where I want it"?

    Without sticking the bike on a dyno how are you setting it up to this "where I want it" AFR? What is your "where I want it" AFR? And how do you know you are running at or close to your "where I want it" AFR?

    I guess what I'm trying to understand is what is the AFR that this unit is attempting to target?

    Or is it simply something you set by feel and HOPE things are within range?

    How is the #1 pot adjusting idle when your setting the pots at 2000 RPM's? I'm really lost on the idle adjustment and what the AFR will be at idle. I would assume the adjustment would be able to set the idle a bit richer than cruise. But it seems the #1 pot is a compromise between the two if its being adjusted at 2000 RPM's.

    I'd like to know more about how it senses loads. If you have some connections and get an answer it would be great?
     
    Last edited by a moderator: Apr 9, 2009