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Closed loop -> open loop switching point ?

Discussion in 'Gen 2 Prius Technical Discussion' started by petrik, May 7, 2011.

  1. petrik

    petrik New Member

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    Any idea at which point the engine mcu (ECU) changes the fuelling algorithm from closed loop (retainging stoich mixture) to open loop (calculating fuel using throttle opening) ?

    Often the switching point is based on TPS (throttle position sensor) voltage. Easiest way to determine this switching point would be to look when does the short term fuel trim calculation stop ?

    The reason for asking is my interest to offset the TPS sensor to allow the car run a bit longer on a closed loop mode - with better fuel economy.

    Usually open loop is calculated using TPS position, ambient pressure, intake air temperature etc * long term fuel trim - without oxygen sensor feedback, so its often tuned to be more rich than the stoich closed loop mixture.

    Anyway prius has two oxygen sensors so I may be wrong with this thinking too - but worth looking into more to squeeze bit more miles out of gallon - or kilometers per litre as we in europe say.
     
    #1 petrik, May 7, 2011
  2. ccdisce

    ccdisce Active Member

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    I am not realy sure how T does it but..

    In the case of the Ford EEC-V it ====> OL based on TPS and RPM and possibly other Scalars. I used this info to run OL as in the OL Air Fuel table was jacked by me to 15.5. I have access to the A/F table. At higher TPS and RPM to prevent burning valves, pistons and catalyst I made it drop back down to the Narrow Band 14.7. I did try using the A/F offset values that I had acces to but they did not provide the limits of adjustability that I wanted.

    In the case of the Prius ECU as it uses a Wide Band o2 sensor I was planning to leave it in CL and adjust it by a factor of 9/8 or 7/8 and see what happens. I probably will have to generate an Interrupt when a Timer expires to avoid cooking the catalyst which could be the way the older H Insight does it.
     
    #2 ccdisce, May 13, 2011
  3. petrik

    petrik New Member

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    Sure, 15.5 is fairly lean. Often the OL CL switching point is based on TPS and LOAD i.e. Vacuum threshold.

    Need to plug in the gauges to check this.

    Whats your TPS% at idle ?
     
    #3 petrik, May 13, 2011
  4. cyclopathic

    cyclopathic Senior Member

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    the easiest way to do it to get a free flowing filter. It would be a really little bit as filter pressure does not differ more then 1" (0.25%) at WOT with replacement filter, several times more if use cold air intake

    Another way would be slotting and re-adjusting TPS.. haven't heard about it in cars but had seen it done on bikes
     
    #4 cyclopathic, May 13, 2011
  5. ccdisce

    ccdisce Active Member

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    TPS is whatever is stock, I have not looked at it in 10 months , since I loaded it into the Scangauge.

    I can see why you want to do this OL as if you did it in CL the ECU will trim out your changes.
     
    #5 ccdisce, May 13, 2011
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