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  1. #1

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    Closed Loop Lambda

    This is were a smiley appears opening a can of worms.


    Okay, Pete will shoot me for asking this but is it available for us PWC guys? If it isn't I am sure there are many good reasons for it.

    I just read a thread about closed loop on the Motec Forum: http://www.motec.com.au/forum/viewtopic.php?f=11&t=725

    And I have noticed that there is a setting in ECU Manager (Adjust > Lambda Control > Setup) that gives lambda control.

    0=off
    1=narrowband
    2=wideband

    Any ideas?


  2. #2

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    Closed loop lambda seemed to work well today in testing.

    The LA live graph followed the excepted line very well and when the I2 logging was cross-referenced to the lambda table every setting I checked was within =/- 0.1 LA.

    Remember this is river testing only.

    Can someone tell me why we "DON'T" use it?

  3. #3
    Professional Alike Racer Clazz. Teerayoot's Avatar
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    I think not a good idea to put LAMDA sensor always on ,
    I have damaged Lamda Sensor for about 4 pcs ,cause by water splash.

    so tired to tune fuel,put more boost need to adjust new fuel.

  4. #4

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    Quote Originally Posted by Teerayoot View Post
    I think not a good idea to put LAMDA sensor always on ,
    I have damaged Lamda Sensor for about 4 pcs ,cause by water splash.

    so tired to tune fuel,put more boost need to adjust new fuel.


    Thanks for the input (I was feeling kinda lonely),

    It is a PITA retuning every change but now I have an ebook it is heaps easier doing it live on the water.

    Are you using a modified waterbox or a stock one?
    Also which lambda sensor are you using?

    I have found that if your using a modified waterbox the splashback of the water gets onto the ceramic heater which causes the sensor to fail.

    Also the more expensive NTK (Not Bosch) sensor seems to last much longer. Maybe due to the design of the probe cone shape and the # of holes.

    My sensor stays in all the time and have only popped one so far and that was my fault anyway, long story.

    If the sensor fails the Motec reverts back to the original tables anyway (as long as they are setup okay?!).

    IMO, and would be happy to be corrected if I'm wrong.

  5. #5
    Professional Alike Racer Clazz. Teerayoot's Avatar
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    I'm using stock water-box,
    not sure Vi-Pec do when sensor fail,
    when it fail sometime it read as very large value,Vi-PEC might not know how to correct it and may assume it might really lean condition,

    where to buy NTK sensor?i will try that one if it can long lasting.

  6. #6

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    Quote Originally Posted by Teerayoot View Post
    I'm using stock water-box,
    not sure Vi-Pec do when sensor fail,
    when it fail sometime it read as very large value,Vi-PEC might not know how to correct it and may assume it might really lean condition,

    where to buy NTK sensor?i will try that one if it can long lasting.
    Sorry, I keep forgetting your on a Vipec system. I'm not biased, I'm just more familiar with Motec atm.
    I'm not sure what LA sensor the Vipec's will accept or calibrate so you better check with Riva.
    I get mine off Gary @ http://www.watsonracing.com.au/produ...n%20Components
    He's the same price as direct from Motec but ask him specifically for the NTK sensor. The prices used to be a rip-off but their now in line with most prices around the internet.

    When the LA sensor fails on the motec it reads a zero value.

  7. #7
    SHOBiz's Avatar
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    I think the benefit of the wideband is that when you are making changes to hardware the lambda can greatly vary so wideband can more easily track it. Where as a narrowband has a small range (0-1 volt) it will read.

    In essence a narrowband is good for a known steady afr situation where it changes little from 14.7. Something like open loop where the sensor is ignored after warm up and the ecu just reads static tables like what I use im my modded 944 ecu.

    A wideband lets you tune to varying situations that can cause afr to change more significantly.

    Imagine running a narrowband and you are rich as tar, but the narrowband doesn't tell you exactly how rich since it is limited.
    Or, being lean at WOT and BOOM because the sensor can't tell you that you are way off.

  8. #8

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    Answer found I think!

    From Pete a while ago:

    Now all that said you can put the ECU into what’s known as “closed loop lambda”.
    The ECU then uses the lambda sensor to measure the current lambda reading and compares that to the Lambda Table (your ideal AFR)
    The ECU then trims the fuel on the fly so that you are always running perfect mixtures.
    It does not however write permanent change to the main fuel Map, it just applies a live over all trim on the fly.
    You get to program its limits for rich and lean and when it clicks in and out of closed loop.
    But why does it not write to the program I hear you ask.

    1. A lambda sensor is not the most reliable sensor, in electronic terms it reacts reasonably slowly so doesn’t give good information on transients.
    2. It is susceptible to failures from leaded fuels and in your case water so can give false readings as it is on its way out.
    3. It can read lean when its not, if the engine is so rich that it misfires then un burnt oxygen flows through into the exhaust and is then read by the lambda sensor (oxygen sensor) as lean

    So in short the lambda sensor can not always be trusted and left unchecked could make a real mess of your fuel map.

    There’s a tonne more to it than that as well but that’s the basics and I hope I have answered your question.

    Cheers

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