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Help understanding GenIII fuel cutoff and gliding

Discussion in 'Gen 3 Prius Technical Discussion' started by F8L, Mar 11, 2012.

  1. F8L

    F8L Protecting Habitat & AG Lands

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    I've tried searching for answers but the complexity of the questions make it hard to enter search words.

    In the GenII I could easily enter a glide or warp stealth and the scangauge II would read 9999mpg, rpm would be around 996 and GPH 0.

    In the GenIII I have tried to glide and I never truly know when I am gliding because when applying the same gliding technique as I would in the GenII the scangauge will read 300mpg - 2,000mpg, 0-996rpm, and GPH is .02.

    Even when lifting completely off the throttle and coasting down a very long steep hill mpg never goes about 1,xxxx and GPH is always 0.02 or higher.

    My question is this some sort of anomaly in scanguage reporting and actual fuel usage is zero or does the GenIII not really have an easily attainable fuel cutoff?

    I've read threads and watched videos on how to efficiently drive a GenIII but there is not much I could find regarding fuel cutoff and gliding.
     
  2. co_prius_3

    co_prius_3 Member

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    It's definitely possible in the Gen3. I've seen the tach go to about 960 RPM and the GPH go to 0.0 when the car is going downhill and my foot is off the pedal. From what I understand about the power split device (PSD) the ICE must keep spinning without load to prevent the motors from over-spinning.

    Based on this simulator, the maximum practical speed in this mode is about 60MPH.

    Due to a bug in the SGII, it will show the GPH as .01 or .02 even the the ICE is off. But the average MPG on mine usually is very close to the Prius number over time if they are both reset at fillup.
     
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  3. F8L

    F8L Protecting Habitat & AG Lands

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    Yeah, that was pretty normal in the GenII.

    I forgot to state that I have observed it go to 9999mpg and 0GPH a few times now that I have over 1000miles on the car but it is difficult to recreate the conditions required for it to do that.
     
  4. co_prius_3

    co_prius_3 Member

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    I've only seen it happen when going downhill at 50MPH or greater.
     
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  5. fuzzy1

    fuzzy1 Senior Member

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    I often saw GPH stuck at 0.02, which caps the MPG to about 3000. I also saw MPG peg at 9999, but didn't have these two gauges displayed enough to track down any clues. These displays were easily sacrificed to watch other items.

    During warmup idling, I don't remember seeing real numbers below 0.20 gph, not all that much less than the 0.30 of my Subaru. Past that, the Prius engine was warm enough to shut down, at least in ECO mode. So I just wrote off those 0.02 gph figures as a communication problem between the devices, not real fuel consumption.
     
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  6. F8L

    F8L Protecting Habitat & AG Lands

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    Warp stealth was possible at any speed above 42mph in a GenII. On my evening commute I had a long steep downhill section that I would usually warp stealth down at speeds up to 80mph. During warp stealth RPMis around 996 and mpg is 9999. Often I would run SOC down to 57.5% at which point the ICE would kick on and mpg would drop to 150mpg or so unless I completely lifted off the throttle to enter regen braking. I found it was better to continue with my foot slightly on the gas pedal to conserve momentum rather than regen brake and slow down.
     
  7. fuzzy1

    fuzzy1 Senior Member

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    My WS is 992 RPM, though often dropping to 960 for a moment as it enters WS. It seems that steady RPMs are usually multiples of 32, with non-multiples showing only when the RPM is changing, though I haven't rigorously checked it.

    Did the Gen2 have the same pattern?
     
  8. F8L

    F8L Protecting Habitat & AG Lands

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    You know, I never really analyzed it but I think it did because the numbers always seemed to be 96x or 99x. I state 996 because that is the best my memory can conjure up but it could have been either or both. It was never 92x or 97x. Does that make sense? lol
     
  9. macman408

    macman408 Electron Guidance Counselor

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    You should be able to use the open/closed loop gauge to tell you whether you're in fuel cutoff or not, at least once the car is warm. Once it's past 70°C EWT, then it should show open loop when the engine is off or in fuel cutoff, and closed loop when it's injecting fuel. I think for a while while it's warming up (not sure how long), it will be open loop. From there, you can get an idea of whether the GPH/mpg gauges are accurate or not. I think fuzzy and co_prius are right that GPH sometimes gets stuck a bit above zero - I think maybe at the last non-zero reading.
     
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  10. F8L

    F8L Protecting Habitat & AG Lands

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    I'll keep an eye on this. I got frustrated with GPH and changed it to engine coolant temp. lol

    I was watching RPM a bit more intently and fuzzy was right. In gliding conditions the RPM was either 960 or 992 exactly.
     
  11. Rebound

    Rebound Senior Member

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    There's a good article about Gen III warp stealth here:
    http://techno-fandom.org/~hobbit/cars/warpstealth.html

    The summary is this: You can cruise in warp stealth at high speeds if you lift the accelerator to kill the engine, then you accelerate enough to discharge 10 amps. I don't have a ScanGauge, so I don't know if it measures charge/ discharge, but that's what the article says. At some point, the battery eventually depletes and the ICE kicks in.
     
  12. fuzzy1

    fuzzy1 Senior Member

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    ^^ In active fuel burning, check to see if steady RPM is still an exact multiple of 32. When warming up, it likes 1280 RPM (32x40). The few other steady figures I checked were also nice multiples, but this pattern fell apart when rpm was slewing.
     
  13. Airman74

    Airman74 Junior Member

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    Newbie here. I just recently bought my 2nd Prius ( a 2010 L3 ) to compliment my 2008 L3. My question here is this : do all the different modes Eco , normal, power make that much difference in MPG?? Or is it more your driving style??? I've read that all these different modes do is change the throttle sensitivity,, is that correct???
     
  14. F8L

    F8L Protecting Habitat & AG Lands

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    They mainly change pedal sensitivity although ECO mode does change AC settings to reduce energy consumption of the AC system which translates into better mpg.
     
  15. SageBrush

    SageBrush Senior Member

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    Dumb question first: Did you set the SG for 1.8L and hybrid mode ?

    I have my old SG attached to the CT. If I am in EV, rpm=0 and iMPG = ~ 1500 -3000
    If I coast over 45 mph, rpm is ~ 1000 and iMPG = 200 - 300
     
  16. F8L

    F8L Protecting Habitat & AG Lands

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    I'm still using my old SGII. I think it is version 3.15 or something. I'll get around to sending it in for an update. For now I am using the Loop gauge which tells me when the engine is truly off and fuel use should be zero.
     
  17. GreenJuice

    GreenJuice Active Member

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    I have both ver. 3.15 and 4.06 daisy-chained, and both have the same issue with GPH=0.02 when RPM=0, so an update may not be a solution at this time.

    Like the figures from SageBrush, I'm getting the same results on my Gen 3 and am struggling to understand why SG's iMPG figures are in the low thousands for a 'below 42 mph glide' but in the hundreds for an 'above 42 mph glide' (a.k.a. WS).

    The sudden step change of nearly a magnitude when Loop is Open for both situations is puzzling. I thought spinning the ICE to protect MG1 didn't burn fuel, or could this be part of the same SG 'bug'?
     
  18. F8L

    F8L Protecting Habitat & AG Lands

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    Good to know. Thank you.

    I have the same questions as you, obviously. It would be nice to figure out what is going on here. It sort of make the SGII sort of useless for a lot of the things that I like to monitor or at the very least causes you to make assumptions based on conclusions attained by proxy i.e. fuel use must be zero because we are in open loop and RPM is 0, 960 or 992. :confused:
     
  19. SageBrush

    SageBrush Senior Member

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    Justin, you are being tripped by something I cannot even see ;)

    In what practical way is 2000-3000 mpg (.02 gph) different than no fuel use ?

    Btw, some time ago Hobbit posted that ICE spin requires about 2 kw. That is about 6 kwh/hour of petrol equivalent energy assuming 33% conversion efficiency, or .18 gph. So a WS MPG(e) reading at 60 mph is 333 MPG(e).

    Coincidence or explanation ? I have no idea
     
  20. F8L

    F8L Protecting Habitat & AG Lands

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    None really. It's still annoying that it is not right. :D
     
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