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  • Closed loop/Open loop

    (From StrokerJlk)

    In response to recent PM's I have received regarding closed and open loop fuel systems.

    closed loop is the areas of the program (map) where the ECU or ECM (whatever you wish to call it) controls the AFR (air fuel ratio) to keep it at 14.7 stoich. (stoichiometric ratio). In order to operate in stoich you have to have the narrow band sensors (stock 06 dynas and 07 up all) you could use a wide band sensor but not going to get into that in this post because they are not needed using a factory ECU.
    closed loop can operate in idle and cruising areas of the map.
    they operate in these areas of a stock configuration.


    open loop is the areas where the sensors are not used to achieve a 14.7 stoich AFR. say WOT (wide open throttle) factory WOT AFR varies from bike model to bike model based on my experience sniffing the exhaust for there AFR.
    stock ECU with no fuel management system uses the open loop in the areas of low vacuum (kpa) somewhere around 60% throttle and up depending on the load that is on the motor.


    So is open loop better than closed loop?
    there are two schools of thoughts on this.
    One is take it out of closed loop and tune every area of the map in open loop say 14.2 at cruise 12.5-13.2 at WOT and 13.8 at idle.
    this is the way you would tune a 06 down bike with no factory sensors so no there is nothing wrong with this method.

    another school of thought is use closed loop in the cruise area and open loop for idle and throttle positions (high load areas) 60 % up to 100% or WOT.

    I use both from motor to motor.
    I like to use the closed loop in some parts of the cruise area for various reasons....fuel mileage, consistent AFR.,and the biggest reason....the ECU is learning while in closed loop . this is to keep the AFR at 14.7 in the areas that are programed to do so. But what the ECU also does is take this info and applies it to the open areas of the map. this helps keep those areas constant also.

    there are times or reasons to tune a bike in either manner..all open loop
    or some areas closed and some open.
    It depends on the type of build it is... all out performance? mild performance? someone that wants mpg? Bar hopper? touring?
    stock throttle body ? aftermarket throttle body. stock injectors ?

    on a stage 1 or stage 1 with cams or even with street port heads and a cam . a combo open and closed works very good in the cruise area of the map.
    although this is where the TTS or SERT tuner comes into play. it allows the tuner (tech) to tune the areas how he feels it should be. or give it what it wants as far as AFR and timing.
    the TTS and SERT allow the tuner to adjust the voltage applied to the sensors to alter that 14.7 a little, to between 14.2 and 15.4 AFR.
    this is called CLB. or closed loop bias.
    If the sensors voltage is turned up enough to maintain a controlled 14.2 AFR (closed loop) in cruise this makes for a very nice cruising AFR on most bikes, while keeping good mpg and drivability.
    There is much more to these theories but I think that covered the questions.

    o- yea FBW or TBW . fly by wire or throttle by wire.
    08 up touring bike are all TBW OR FBW this means the throttle doesn't have a throttle cable to open up the butterfly. the ECU controls the throttle. the stock ECU on the TBW or FBW the throttle is not allowed to go to 90%-100% throttle until after 2600 rpms. some seem more like 3000 rpms. but the factory says it's 2600 rpms .
    **Note: The technical info I provide is suggestive. I am not a perfeshunel.

    "No two motorcycles should be the same. Your bike should be based on your creativity, and whatever's going on in your life at that time..." Jesse James


    HERD Member #10
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