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Difference between closed loop and open loop?

Discussion in 'Technical and Troubleshooting Torque' started by Fa1c0n, Sep 25, 2014.

  1. Hi guys,

    So I bought a Power Vision for my bike to tune it on the fly. So far so good. Seems to work well.
    I was playing around looking at the "Quick Tune" settings and I have a tick box for "Closed Loop".
    It is ticked by default.

    Can anyone explain the difference to me and any hazard a guess as to what would happen if I untick the option of "Closed Loop"?
  2. Does your bike have an O2 sensor? If not, it's running on Open Loop.

    Open loop means the settings are fixed and the ECU does not take a reading from the O2 sensor to adjust the A/F ratio. My CB400 does not seem to have an O2 sensor.

    Wouldn't want to speculate as to what will happen if you select or deselect the option, though...
  3. the O2 sensor "closes the feedback loop", so the ECU knows if lean or rich..

    BUT, is only used at time when you want a stoichiometric mixture (14.7:1), ie, idle, and cruise.
    under part-full throttle, the closed loop disengages, and the ECU runs open loop.
    reason for that is a normal narrow band O2 sensor can only tell when it is rich or lean, but for power you want a richer mixture.

    ECU should have a % it can adjust the idle/cruise mixtures away from the programmed map.
    if you untick closed loop, and the mapped mixtures are out, it could run rich/lean, at idle/cruise...

    you should get better economy with closed loop enabled, and it won't affect part to full throttle (as long as ECU disables it as required)

    there is no reason not to have closed loop enabled
    • Like Like x 1
    • Agree Agree x 1
  4. Bah - beaten by oldcorollas.....

    Posted almost verbatim.....

    You don't need to read it twice.
  5. I may have misunderstood what you said oldcorollas. But under part throttle it stays closed loop. Only under WOT does the ECU go open loop. But that's just my experience with BMW Bosch motronic in my old car, not qualified opionion!

    As said unless you have a O2 sensor, closed loop cannot work. It will just run in open loop if selected I assume.
    • Agree Agree x 1
  6. I said "part throttle" because it totally depends on how it is programmed!
    some systems purely use a switch on the TPS, so above X% opening, it turns off. some use a certain manifold pressure, above which it turns off.
    some systems incorporate both of the above, plus an RPM cutoff too...

    it really depends on the motor in question, as some motors are under significant load at half throttle, and some aren't :)

    from memory, I had my MS2 tuned so that closed loop was disabled below 2000rpm (1500rpm idle speed), above 6000rpm, and between 2-6000rpm it was enabled only when manifold pressure was below... I forget the value :).. and I think it was only on below 20 or 30% throttle?
    anyway, various values had a say in turning it on or off

    some details of MS options here (there is coolant temp trigger too)
  7. That is what I wanted to hear! :)

    Thanks for the tip.
    I am going to post another thread about my experiences with the power vision unit soon. Up to my 5th tune this morning and will do another on the way home. So far my top and middle has become much, much better, but between 1% and 5% throttle I am having issues. :-/