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Thread: Lowest Load value doesn't seem low enough

  1. #11
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    Hmm ... well that doesn't make much sense to me ... as I imagined you'd need a reference signal for demand on the engine (TPS), a measurement of the supply of air for fueling (MAP/MAF), and a feedback signal (O2 sensor) to really determine the load of the engine in my mind ....

    However, I am VERY much not a DDFI 3 specialist ... But I'm definitely interested in digging further into how DDFI 3 does it's magic ...

  2. #12
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    Quote Originally Posted by ich
    stimmt nicht für ddfi-3.
    ich, I would love to learn more about this. What is the ECM's additional -input- for determining load on DDFI-3?

  3. #13
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    Quote Originally Posted by ich
    stimmt nicht für ddfi-3.
    Aah, is it the MAP sensor on the 1125? I could easily see that as an input for determining Load, on the 1125. I keep forgetting that not everyone has an XB like me :) So i'll take a stab: on XB's, Load as an input for the Fuel tables is probably derived from TPS alone (my former statement, which is corroborated by the Tuning Guide V2) . On 1125's, Load is probably derived from TPS and/or MAP.
    Does that sound right?

  4. #14
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    nö. raten ist immer scheisse. messen ist besser.

  5. #15
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    ich, unfortunately I don't understand German, and a google translation of your last response didn't make sense to me.

  6. #16
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    ich, please comment. I said that our ECM almost certainly determines the Load value from the TPS alone. You replied "Not true for DDFI-3".

    Why is it not true for DDFI-3?

  7. #17
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    Well ... the XB's lack the MAP sensor the 1125's have ... so you've got nothing to give inputs to the ECM except for the TPS itself ... these are still alpha/N systems with O2 correction ... DDFI 3 is just the next evolution of it ...

    I could (with a stretch of the imagination) see the ECM taking into account the speed at which the TPS value changes, along with engine speed, to make up some kind of "load value" ... Because, if you crack the throttle open in a very quick motion and the engine revs start climbing to match ... it's under a load ... mayhaps that might be the source for this value for the ECM ...

    Hmmmm says I ...

  8. #18
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    Alpha-N by definition is TPS and RPM only. I have found no evidence that any generations of DDFI, by default, use any other method, including on the 1125.
    Take a look at this diagram:
    TPS and RPM and the ONLY values ever used as Fuel and Timing table lookups. I trust Nick Pashley as a credible source, but of course he could be wrong in some areas.

    Even in the 1125 Service Manual, it clearly states that Load = TPS.
    Section 6.1:
    "- Engine load measurement via throttle position sensing"

    And in section 6.3 "Throttle Position (TP) Sensor:
    "The output of the sensor is a voltage, dependent on the position of the throttle plate, and used by the ECM to determine ignition timing and fuel required at any given RPM and engine load"

    There is an EEPROM table called "MAP to Load Table MAP Axis", but I don't see any evidence of it being used. I checked BUEOD (feature not even available), BUEYD, BUEZD, BUE1D (XB9), and BUE2D EEPROMs and the feature "TPS and MAP Load Setup: Enable TPS/MAP load feature" is disabled, and the "MAP to Load Table MAP Axis" tables are empty. Additionally, when I suggested MAP as a factor for Load calculation on DDFI-3, ich said "nö. raten ist immer scheisse. messen ist besser" which I cannot decipher (though I do know what "no." means, in German). I have stayed up past 2am the last several nights trying to figure this out, all based on ich's statement that I am wrong for DDFI-3. Without more info, I don't see how MAP factors into this. I was just trying to give ich the benefit of the doubt. I would test this but I don't have an ECM that supports this "Enable TPS/MAP load" feature.

    Our ECM does account for the increased fuel needs during acceleration! BUT, I would bet a cookie that fuel addition percentage is made AFTER the values are grabbed from the Fuel Maps :). Unfortunately, where the ECM makes the Accel Enrichment is not documented in any text or diagram that I can find. My theory could be tested by making a throttle stop, say midways between throttle grip closed and open. Compare the max load value between the following cases while datalogging:
    a) throttle very slowly opened to the stop, and
    b) throttle quickly opened to the stop
    For case b), if the max observed load value is greater than case a), then the ECM's algorithm for adding Accel Enrichment fuel is to temporarily increase the Load value. I just don't see that happening. Every other fuel adjustment is made after the TPS/RPM lookup.

  9. #19
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    Fun stuff!

  10. #20
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    While the DDFI-3 has MAP sensor tables, neither the XB or 1125 models ever utilized a MAP sensor from the factory. The 1125 models have a Barometric pressure sensor (same sensor but samples pressure before the throttle plates) but not a MAP sensor. I am slowly working on a DDFI-3 setup for my XB that will utilize the MAP sensor and TPS to determine load. It is quite a project, though.



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