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Thread: Idle control (bac) settings for a 20v on haltech

  1. #1
    Toymods Club Member 1st year Apprentice
    Join Date
    Mar 2014

    Default Idle control (bac) settings for a 20v on haltech

    Hi all. Anyone know the frequency and suggest any settings for a 20v idle control (bac) with an old haltech


  2. #2
    Fustrated DYI mechanic Automotive Encyclopaedia Omegaman's Avatar
    Join Date
    Oct 2005
    Sydney N.S.W

    Default Re: Idle control (bac) settings for a 20v on haltech

    See if this info helps. i havent read it to compare it to yr requirements

    Please note that this is a simple guide and some things may change
    from one
    car to the other. I am going to base this article on the Series
    4/5 13BT
    motor, which so many on the Haltech list have.

    BAC , WHAT IS IT ?
    First of all a description of what BAC idle control is and what it
    BAC stands for Bypass Air Control. It is a system where a passage
    of air
    around is setup around the throttle plate to allow the engine to
    raise and
    lower in rpm. This variation of rpm is usually controlled via a 2
    or 3 wire
    solenoid. This solenoid is pulsed at a particular frequency, which
    from solenoid to solenoid. It is the length of each of these
    pulses that
    determines how much air is allowed to go in. The larger the time
    the more
    the valve is head open and the more air goes in. The more air that
    goes in
    the higher the rpm. This is all controlled by the ECU.

    I will cover the 2-wire types here, but 3-wire BAC slave type
    systems are
    very similar. You should also not try and enable your BAC or fine
    tune it
    until your motor is completely tuned. Having tuning issues around
    the idle
    speed region will make it difficult to set up the BAC.

    The 2-wire types are very easy to wire up. All you need is to
    select a PWM
    wire that you have free, and run this along with a 12V+ Grey/Red
    wire to the
    BAC valve and connect them. It should not matter which pin is
    positive or
    Now, if you go online with your Haltech, go to the PWM Output
    Options page
    by hitting CTRL-W.
    Go down to the PWM output number that corresponds the the wire you
    to the BAC, and with the TAB key toggle through until you get the
    BAC Valve
    option. When you do, hit the ENTER key. This will lock it in as
    desired output. It will then give you two options under BAC
    Valve. One os
    to Enable or Disable the feature, the other is the Period (or
    frequency) at
    which the solenoid will be pulsed. This value is usually found
    through exper
    imentation, or by simply asking someone who has done it before.
    On the
    13BT motor which I am using as an example, the I have found to work
    well is
    around 24ms. Others may find values that differ, so use whatever
    works best.
    Once Enabled the BAC output will start to function and now needs to
    setup. Do not Enable the BAC at this point, we have other areas to

    Here is where it gets a little confusing. If you go to the Output
    page by hitting CTRL-O, you will see the Idle Speed Control
    feature. In
    order to use BAC this feature needs to be left DISABLED. The
    settings here
    will still work but only if left in Disabled Mode. If Enabled the
    E6K will
    think you are trying to run a 4-wire stepper motor for idle
    control, and not
    a BAC valve.

    What needs to be done now is to set the throttle stop. What we
    need to do is to setup the throttle stop to maintain idle speed
    around 50 to
    150rpm below the Target Idle Speed we wish to obtain. Once this is
    done the
    throttle stop can be locked and the TPS will need to be
    recalibrated. If the
    TPS reads anything other than 0% or 0% Fault then the BAC function
    will not

    The next step is to go an Enable the BAC Valve PWM Output. Hit
    CTRL-W and
    go down to BAC Valve and change it to Enable. Once done go to the
    Options page and you can start adjusting the Idle Speed Control
    Remember to leave this feature as DISABLED so that the settings
    will effect
    the BAC and not try to use the 4-wire stepper motor.

    This is a short summary of what the Idle Speed Control settings
    do. This is
    based on Firmware 14 and software 6.34 which is the current release
    at the
    time. Some settings may differ if you are using another software
    firmware version.

    Target Idle Speed - This one is pretty obvious. This is the idle
    that you wish the engine to be at under normal conditions.

    Cold Idle-Up RPM - This is the amount of RPM added to the Target
    Idle Speed
    when the coolant temperature is below the amount set under Cold
    Temp. Limit.

    Start RPM - The amount of RPM added to the Target Idle Speed for
    the first
    20 seconds after starting the motor. It is done to help stabilise

    Number of Steps - This sets the increments in which the BAC is
    It is another word for sensitivity. I usually start around 100 and
    use trial
    and error from there.

    Cold Temp. Limit - The value under which the engine is considered
    to be

    Cold Min Position - The minimum duty the solenoid will be pulsed
    at while
    the engine coolant temp is below the figure set in the Cold Temp.
    More on this later.

    Hot Min Position - The minimum duty the solenoid will be pulsed
    at while
    the engine is at operating temperature. More on this later.

    Cold Opening Position - The duty at which the solenoid is run
    cranking while the engine is below the Cold Temp Limit. It is to be
    higher than the Cold Min Position and acts the same way as opening
    throttle during cranking.

    Hot Opening Position - The duty at which the solenoid is run during
    cranking while the engine is at operating temp. It should be set
    higher than
    the Hot Min Position.

    After we have the car idling on the throttle stop and we have
    Enabled the
    BAC, this is the process to go through to obtain the best idle speed
    control. Setup should be done initially with the engine at
    operating temp,
    then later go through and do the cold engine settings.

    First we need to set the Target idle speed. Easy enough to do. If
    we want
    900rpm idle then set it to 900.
    Next to setup is the Hot Min Position. This is rather simple to
    do. Set a
    target idle speed that is really low. Say 500rpm. This will cause
    the BAC
    to almost completely turn off and rely on the throttle stop to keep
    the car
    idling. If everything is working correctly then you should have the
    idling on around 800rpm if the throttle stop is correctly setup.
    What we do
    now is to increase the Hot Min Position until the revs start to
    rise. When
    we can get an idle just below 900rpm (the target idle speed) then
    the Hot
    Min Position is set. We can now change the Target Idle Speed back
    to 900rpm.
    Next on the list is to do the Hot Opening Position. To do this you
    set a
    value a little higher than the Hot Min Position. I usually add
    around 20%
    to it. Now switch off the engine and try to restart. If the engine
    revs are
    low and build up try adding more to the Hot Opening Position. Is
    the revs
    are too high then lower the value.
    The Start RPM can now be set. This just keeps the rpm a little
    higher for
    the first 20 seconds. A value around 100 or 200 is good enough for

    You will have to let the engine sit overnight to be able to do the
    settings. These are done the same way as the Hot settings and will
    almost always a higher value. Putting in values around 20% higher
    than the
    Hot values is a good starting point and adjust from there.
    First up is the Cold Idle-Up RPM. This can be set so that the RPM
    is a
    little higher to warm the car up faster, and is set to the users
    A good starting point is 200rpm higher but a higher value is
    The Cold Min Position can now be set. Try increasing this value
    until the
    rpm rises above the Cold Idle-Up amount. ie if we have a Target
    Idle Speed
    of 900 and a Cold Idle-Up of 200 then while the engine is cold it
    will idle
    at 1100rpm. If we increase the Cold Min Position until the rpm
    just starts
    to go higher than 1100rpm, then drop it down a little we will have
    it set to
    its optimum.
    The Cold Opening Position can now be set in the same way the Hot
    position was set. this will be higher in value than the Cold Min

    That just about does it. If followed step by step all should work
    well. If
    you find the BAC stops working, try checking that the TPS still
    reads 0% at
    idle. If it fluctuates between 0% and 1% then contact me and I
    will show
    you how to get around this.

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