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    lamebums Member

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    Hi all--

    I recently (as of about ten days ago) bought a 2007 Prius from Steve's place, Autobeyours. It took me a while to work out the kinks, but I've been able to extract some pretty good mileage out of it once I got the tires pressed up properly and read up on how to stretch the fuel just a bit further, especially with SHM and similar techniques.

    However, I've noticed an issue with SHM - I know that in theory one holds 14IGN/18TPS on the scangauge at (insert your low 50's MPH speed here) to hold the fuel consumption meter at roughly 1.5x speed or better, which I have seen plenty of times.

    However sometimes I've found it completely impossible to hold 18TPS for more than a second or two - it'll suddenly and inexplicably jump to 21TPS without the IGN changing or my foot moving at all. And when I try to back off the accelerator, it instead drops into warp stealth, with 5IGN and 14 TPS . Given the largely flat areas I drive on and already lower-end speeds I drive, it means I have to re-accelerate in a hurry and it costs me a bunch of mileage. Here's a couple shots of the fuel consumption display - on one day, the car behaved properly, and on the other, 18TPS was impossible to hold. Mind you, this was over the same stretch of highway:

    This is with the Prius behaving properly:
    [IMG]


    And when 18TPS was impossible to hold:
    [IMG]


    One thought: I considered the possibility that driving at night would increase the electrical load (headlights, etc.) and potentially put further load on the hybrid battery's SoC, but figured the warmer temperature might mean the fuel economy was a wash?

    Does anyone have any thoughts/known causes of the Prius being unwilling to hold 18TPS and instead jump to a higher number (and burn much more fuel)?
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    Cory151 Junior Member

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    What scan gauge are you using?
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    lamebums Member

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    Hi Cory151--

    I'm using a ScanGauge II, version 3.15. I bought it in early 2008.
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    GreenJuice Junior Member

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    Factors that might affect how easy it is to hold SHM include the gradient of the terrain and SOC.
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    lamebums Member

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    Hi GreenJuice--

    The issue isn't being able to hold speed on gradients - I generally only use it on flat or gently downhill slopes.

    What I'm saying is I back off to 18 TPS/14IGN, and then after about 2-3 seconds, TPS jumps to 21, IGN is still at 14, and instantaneous MPG has dropped from 90 to 65, with no appreciable difference in performance. If I try to back off the pedal to compensate and get it back to 18 TPS, it just drops into warp stealth instead at 14 TPS.
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    seilerts Battery Curmudgeon

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    It is entirely dependent on SoC. Your graphs look exactly like the difference in fuel economy for 5-6 bars vs. 4 or less bars respectively.
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    GreenJuice Junior Member

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    Yes, I wasn't referring to holding speed either. I was referring to holding the SHM 'state' as defined by that combination of TPS and IGN.

    I don't know the precise programming logic for the ECU but I can confirm the observations of others that the car will try to get SOC to 60% as soon as conditions allow it.
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    lamebums Member

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    Hi GreenJuice--

    I've noticed this, especially when I take the Prius out on the highway. And you're correct inasfar as that the Prius simply refuses to drop to 14/18 when SoC is less than ~59. It'll drop into warp stealth, and if I nudge it back out, it will hold 13/18 or 14/18 for about one second, with the IFCD at ~90 MPG like it should, but then with no difference in performance or acceleration it'll jump to 21 TPS and iFCD drops to ~65. If I try to back off TPS below 21 by easing off the gas pedal, it just drops back into warp stealth.

    To minimize this, I try to hypermile as much as possible when around town, keeping SoC between 60 and 65, although it does drop to 57-58 from time to time.

    (Side note: I've also noticed that the only way to avoid killing your battery down to two bars when stuck in the S1 warmup phase is to hit the throttle wide open, and to hell with the emissions. Either that or limp around accelerating more slowly than most public transit, getting < 15 MPG the entire time.)

    Problem is, I've noticed it happens about 10-15% of the time even when SoC is conisderably higher (I could get on the highway with a SoC of 65 and still have the same 14 IGN/21 TPS problem, pulling less than 70 MPG even when trying to coast down in speed.
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    uart Senior Member

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    Another option is to just leave it in park and let it idle for about 40 to 45 seconds at start up. Then another 10 to 15 seconds of easy driving and you're through S1 without putting any strain on either the electrics or the ICE.
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    Jaquimo Paraglider, Prius glider...

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    This week I also encountered the same thing. I could not get my trusty steed to get better than 4.8 l/100km (49 mpg) while attempting an elusive SHM. This happened after starting to drive from a standstill, without stopping, up to 80~100km/h (50~60 mph). I am using the Torque app to monitor everything but I just could not coach the Prius into SHM.

    Then I remembered the thread about the different stages of the Prius. It seems to me that you need to come to a complete stop in order to get into S4. So I stopped and forced S4 by keeping one foot on the brake while pressing the accelerator until the engine started. After about seven seconds the engine stopped which confirmed that the Prius transitioned from stage S3 to S4. When I then attempted SHM my trusty steed immediately consumed only 3.8 l/100km (62 mpg).

    http://priuschat.com/forums/knowled...12919-five-stages-prius-hybrid-operation.html
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    lamebums Member

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    Hi Jaquimo--

    This may be the cause of the lack of willingness to go into SHM. Most often when I get on the highway, the entrance ramp is about four blocks way from the house. Oftentimes I'm barely out of S1 when I start accelerating on the entrance ramp. Granted, it dumps me onto a construction zone ill-suited for SHM (heavy traffic, etc.) but even after 5-10 minutes on the highway it still won't go into SHM. Perhaps it's because I'm stuck in S3 purgatory because I never truly have a chance to stop the car again? I'll have to check into this more.
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    Tideland Prius Moderator of the North

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    It's possible. The Gen 2 requires a complete stop. The programming has been adjusted for the Gen 3 and it will go into S4 on the fly which is something I appreciate.

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