Help understanding GenIII fuel cutoff and gliding

I pulled GPH and MPG back up today, though not until after initial warmup. Haven't yet watched Loop in this car.

I'm getting 0.02 GPH all the way up to 60 mph (local limit), and seeing Warp Stealth MPGs up to 3000. (60 mph / 0.02 gph = 3000 mpg.) Separately, I'm seeing the ICE actively burning fuel with MPG up to 300 (60 mph / 0.20 gph = 300 mpg). Remember that the ICE will sometimes burn fuel not for propulsion, but instead for heating the engine, heating the catalyst, or charging the battery. It burns far more than 0.20 gph at the start of the warmup cycle, gradually decreasing as it warms, then abruptly shuts off from (approximately) 0.20.

Thus, my interpretation is, for speeds from 20 to 60 mph:
(*) MPG in the thousands (1000-3000): ICE not burning fuel, Prius<->SGII bug prevents 9999 reading;
(*) MPG in the hundreds (100-300): ICE is idling, burning fuel for whatever reason, display reading is approximately accurate;
(*) MPG in between for a single display update (one second): ICE transitioning between modes;
Any steady (more than one second) display reading in between 300 and 1000 mpg does not fit my interpretation unless the current speed is outside the 20-60 mph span.

 

.02 gph thing is annoying. I find if I want Warp Stealth I look at the scan gauge for minimal amps either plus or minus and 992 rpm.

The other minor frustration is the scan gauge update lag which may take a moment to react to your pedal change which may cause you to make another pedal change.

 

FYI,
My equipment (SuperMID) measures the fuel injector on time and I saw no fuel usage on the highway downhill on both Gen2 and Gen3 Prius.

I've heard ScanGauge has some limitation to detect the fuel-cut mode.

Ken@Japan

 

^^^ Which mode are you running in? ECO mode is more aggressive in shutting off and using battery.

With respect to to break-in it will take at least a couple oil changes, it will keep getting better even after 10K mark.

 

In my earlier post, I should have added that (like FL8) I'm also seeing the other MPG=9999 'state', which adds to the confusion about what SGII is displaying (or trying to display).

I follow your deductive reasoning, and have been testing for possible alternative explanations over the last week, e.g. is there a link to SOC?

I'm coming to a realisation that these could all be variations of the same 'fuel cut' states with errors in SGII, as advised by Ken.

 

All I can say is lucky you bought another Prius, and not a Veloster

 

Got stuck in a long segment of bumper-to-bumper single file traffic yesterday, so I had a chance to do some more testing. Also, I decided it was best to RTFM again(!). Interestingly, the SG manual says you will see MPG=9999 if SGII 'improperly detects fuel cutoff', implying that it considers this reading an error!

All tests with engine warmed, in ECO mode, SOC mostly 50-60%. I used the ver. 4.06 SGII because it allows a setting for 'fast' updates from the ECU.

It is possible to improve matters slightly by using a different Fuel Cutoff setting in the SG Setup page. No throttle TPS shows 15 on both my ver. 3.15 and 4.06 SGIIs, so I tried a variety of settings below the default of 24, including zero which apparently 'disables fuel cutoff sensing'. Setting TPS=0 or 16 gives GPH=0.01 more frequently than 0.02, so I'm guessing it is more accurate. (Setting zero seems to make no difference, possibly because I have 'Hybrid' setup elsewhere?)

With fuel cutoff detection set on TPS=16, I found:
1. Rolling forward from stop, foot off all pedals, picking up speed on a minimal downgrade. MPH from 5 rising to over 20 (SG updates are still intermittent, so there are slight errors in the timing of my readings). Open Loop. GPH=0.01 , MPG readings from 60 rising to 2000

2. Same as above with car in N instead of D, rolling down a steeper downgrade. Open Loop. GPH=0.01, same range of MPG readings as MPH rises.

3. Coasting then gliding down from 60 mph to 30 mph. Foot off all pedals, then reapply gas pedal to get BTA around +1 amp. TPS stays at 15(why?). Loop Opens as soon as HSI goes blank, from then on GPH=0.01, RPM=992 (after flashing briefly at 960). MPH readings start in the low hundreds 200-600 mostly. Step change as speed drops through 42-44 MPH. RPM drops to zero. MPG goes up to low thousands 1200-3000 mostly.

If these are all fuel cut states then:
a) Open Loop seems a reliable indicator for ICE-off fuel cut.
b) RPM=0 (or 992/960 above 42-44 mph) seems reliable as a surrogate measure of fuel cut.
c) the step change in MPG readings below and above 42-44 mph might be related to (b), but unrelated to fuel cut, therefore these readings are errors or a bug.
d) With SGII up to current ver.4.06, set for Hybrids, all GPH and MPG readings are errors when Open Loop (fuel cut, ICE-off)

These errors in instantaneous readings are minor and probably not significant, but I wonder if they could be translated into the cumulative readings over time, e.g. Trip, Day averages, etc.. Could these be possibly unreliable too, and therefore more unreliable the more time is spent with fuel cut?

Could this be tested by seeing what SGII reports for 'a trip that uses no fuel', e.g., a long downgrade or someone with a Plug-in Prius?

 

Hi-mate I am new from Hong Kong and I just ordered a UK made Auris Hybrid and starts looking for fuel saving techniques.

I read a number of people saying in Gen3 prius it is not possible to detect from dashboard info. when performing glide (below 45MPH) or wrapstealth (above 45MPH). As the Auris will have a slightly different dashboard showing the status of charging / eco / normal / power, would it be possible to detect glide / wrapstealth by simply looking at this meter?

Any guess what would the pointer points to when doing glide / wrapstealth?

Thanks.