1. Attachments are working again! Check out this thread for more details and to report any other bugs.

'16 real MPG

Discussion in 'Gen 4 Prius Fuel Economy' started by DieselHybrid, Dec 31, 2015.

  1. krousdb

    krousdb NX-74205

    Joined:
    Jul 16, 2005
    580
    498
    47
    Location:
    Raleigh, NC
    Vehicle:
    2016 Prius
    Model:
    Two
    It depends on the circumstance. If you take a short trip when the car is already warmed up, you will get very pleasing numbers. If you take a short trip when the car is cold, you will be extremely disappointed. Once you get past the cold start penalty, the rest of the time while "warmed up" can be easily in the 80's. The longer the trip, the higher your numbers.

    It takes me 20 miles to overcome a cold start and get the average from start over 70. 2 to 4 mile trips won't get you fully warmed up unless you have very warm weather. For a 2 mile trip, I walk. For 4 miles, I walk or bike. Don't forget your umbrella.
     
  2. JohnF

    JohnF Active Member

    Joined:
    Aug 22, 2009
    497
    428
    0
    Location:
    Essex, CT
    Vehicle:
    2016 Prius
    Model:
    Two
    Do you think it is also possible that the short trips started with engine already warmed up, battery fully charged, and at low enough speed that the car ran EV for a significant portion of the trip?
     
  3. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,463
    38,101
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Isn't there's something at startup, "closed loop" vs "open loop"? Both loops are over my head, but maybe there's less "open loop" with 2016?

    There was a thread here: a guy was trying to justify leaving his car on while gassing up, to avoid the closed loop. Maybe the ultimate penny wise, pound foolish.
     
  4. Coast Cruiser

    Coast Cruiser Senior Member

    Joined:
    Mar 12, 2016
    2,267
    2,571
    0
    Location:
    Pacific Coast Highway
    Vehicle:
    2016 Prius
    Model:
    Three
    Ok, here's the REAL short trip numbers for you Hyper dudes. (I actually paid attention to it.) 2.5 miles. Is this supposed to be important??? Mean something? I got bigger fish to fry. I'm not that bored yet! :LOL: :ROFLMAO:
     

    Attached Files:

  5. krousdb

    krousdb NX-74205

    Joined:
    Jul 16, 2005
    580
    498
    47
    Location:
    Raleigh, NC
    Vehicle:
    2016 Prius
    Model:
    Two
    There is something to that. With the Gen 2 & 3, after powering down, powering up again always resulted in the engine starting and idling for around a minute. With Gen 4, that does not happen. In fact, even after 24 hours, if the temps are above 60F, I can power up and drive thru the neighborhood without the engine starting. The engine starts only when your battery is low or your power demand is too high.

    Sure. At least once a week, on the way home from work, I stop at the grocery store just outside the entrance to my neighborhood. From there to my house it is about 0.7 miles on a downward slope. I mainly coast with some regen before the speed bumps. The engine never runs and the battery level stays the same. Trip from start shows 199.9 MPG.
     
    #185 krousdb, Apr 14, 2016
    Last edited by a moderator: Apr 17, 2016
    Trollbait, breakfast, krmcg and 2 others like this.
  6. krmcg

    krmcg Lowered Blizzard Pearl Beauty

    Joined:
    May 15, 2008
    2,592
    2,388
    0
    Location:
    Whittier, CA
    Vehicle:
    2016 Prius
    Model:
    Four
    In my gen 2, I would always leave the car "running" when I went into the convenience store to get a soda or when I stopped at the ATM and waited in line to avoid the restart penalty. I don't need to do that anymore...
     
    Trollbait and bwilson4web like this.
  7. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,066
    15,372
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    You've given me an idea:
    • Use A/B trip meters - to measure cold start overhead
    • Reset B at work and leave car running - to measure idle overhead
    • Compare idle fuel burn versus cold-start - there should be a break-even point where the cost of a restart equals the fuel burned sitting in idle
    Actually I will use a more sophisticated, recording OBD. This will let me accurately document what happens during the test.

    Bob Wilson
     
    #187 bwilson4web, Apr 14, 2016
    Last edited: Apr 14, 2016
    krmcg likes this.
  8. Maroon

    Maroon Member

    Joined:
    Jan 18, 2013
    159
    88
    0
    Location:
    Tupelo, MS
    Vehicle:
    2010 Prius
    Model:
    III
    I know in VW parlance "closed loop" is when the engine bases fueling on the MAP sensor readings, before the oxygen sensor(s) and catalytic converter are warmed up. Once the O2 sensor and catalytic converter are up to operating temp, fueling duties switch to the MAF sensor for "open loop" operation. As you might imagine, "open loop" operation is more efficient.
     
    Mendel Leisk likes this.
  9. Weasle543

    Weasle543 Member

    Joined:
    Apr 14, 2016
    55
    38
    0
    Location:
    Ohio
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Closed loop will provide more accurate/efficient fueling. During open loop operation the computer's requested AFR is not adjusted/trimmed based on O2 sensor signal.

    Good youtube video explaining open/closed loop operation


    Very good explanation of fuel trims by Paul Danner, quite long, but lots of great info.
     
    krousdb likes this.
  10. Trollbait

    Trollbait It's a D&D thing

    Joined:
    Feb 7, 2006
    21,590
    11,212
    0
    Location:
    eastern Pennsylvania
    Vehicle:
    Other Non-Hybrid
    Sounds like the gen4 doesn't automatically turn on the ICE at start up above a certain temperature and SOC level. Instead, it waits until there is a higher power demand before starting the warm up cycle. Those engine off miles can drive up the average MPG, but the electric used will ultimately be replaced by burning gasoline.

    The gen4 has reduced the warm up penalty, but it is still there.

    Oxygen sensors need to be hot in order to work. Testing an old one involved looking for a current change while applying a propane torch to it.

    While cold, the oxygen sensor isn't sending a signal to the ECU. Without that signal, the ECU doesn't know if unburnt oxygen is getting past the cylinders or not. Without that info, it can't make adjustments to the air:fuel mixture without possibly going too lean, and producing NOX. So it uses a default fuel trim map that tends to be on the rich side. Using that default is when the car is in open loop.

    When the oxygen sensor is working, the car is in closed loop because it is now getting feedback about the outgoing exhaust. The ECU can then lean out the fuel mix until the sensor reports oxygen in the exhaust, and then the ECU backs off a bit on the leaning. So less gas is used while in closed versus open loop.

    Basic oxygen sensors relied on the hot exhaust gases to heat them up, which took time. Modern ones have their own heating element, and closed loop can be reached in under a minute. There are also wide range oxygen sensors that give a more accurate reading of the oxygen level. The gen4 now uses one, but they have been around since the 1992 Civic VX, possibly before that.

    There is a second bank of oxygen sensors downstream of the catalytic convertor, but they are for monitoring the cat's operation, and aren't used by the ECU for running the engine.
     
    Bay Stater and Mendel Leisk like this.
  11. krousdb

    krousdb NX-74205

    Joined:
    Jul 16, 2005
    580
    498
    47
    Location:
    Raleigh, NC
    Vehicle:
    2016 Prius
    Model:
    Two
    I watched the whole thing. The good stuff is the second half when he shows the scanner and how the STFT and LTFT react to a vacuum leak and adding propane to the intake. LTFT reacts in less than a minute. I thought it would take much longer. It makes me re-think what happens when switching from E10 to E0 or vice versa. You will run rich or lean only during open loop when the STFT is not yet enabled. So any change in fuel economy due to ethanol or lack thereof could be immediate, or at least after the next time you go into closed loop.
     
  12. Maroon

    Maroon Member

    Joined:
    Jan 18, 2013
    159
    88
    0
    Location:
    Tupelo, MS
    Vehicle:
    2010 Prius
    Model:
    III
    Thanks, Weasel. I had it backwards! :(
     
  13. krousdb

    krousdb NX-74205

    Joined:
    Jul 16, 2005
    580
    498
    47
    Location:
    Raleigh, NC
    Vehicle:
    2016 Prius
    Model:
    Two
    I had a 92 Civic VX and I remember how expensive it was to replace the heated O2 sensor. I also had a digital voltmeter monitoring the O2 output so I could tell when I was in lean burn mode. I had another DVM hooked up to the fuel tank level sensor, measuring ohms so I knew the fuel level because the gauge in the dash went bad. Those were fun times.
     
  14. Trollbait

    Trollbait It's a D&D thing

    Joined:
    Feb 7, 2006
    21,590
    11,212
    0
    Location:
    eastern Pennsylvania
    Vehicle:
    Other Non-Hybrid
    It wasn't just heated, the oxygen sensor was also wide range, and likely not a regularly stocked part for the times. Hopefully, the part costs have dropped for modern applications.
     
  15. William Redoubt

    William Redoubt Senior Member

    Joined:
    Feb 13, 2016
    1,215
    1,164
    1
    Location:
    Coronado Island, California
    Vehicle:
    2016 Prius
    Model:
    Two
    My Prius Two (not Eco) came with the Enasave 01 A/S tires.
     
  16. Weasle543

    Weasle543 Member

    Joined:
    Apr 14, 2016
    55
    38
    0
    Location:
    Ohio
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Open loop fueling will typically be rich of stoichiometric (14.7:1). Also O2 sensor temperature isn't the only parameter used to go into closed loop, coolant temperature is another. A thermostat failed open can cause an EFI engine to take longer to go into closed loop or maybe not at all. Depends on how it's programmed.

    Remember that STFT is trying to keep the O2 sensor signal at stoich (or requested/commanded AFR) and LTFT is trying to keep STFT close to 0.

    Ethanol content in gasoline will effect fuel trim because alcohol has less BTU (and hydro carbons) per unit of volume than 100% gas. Google ethanol stoichiometric air fuel ratio, its 9:1. Considerably richer than 14.7:1 of gasoline. Therefore once in closed loop operation the O2 sensor will be sending a leaner signal to the computer. When the computer compares this to the requested/commanded AFR the STFT will begin to increase. The more positive the fuel trim (both short and long term) the more fuel is injected and burned, why you see a lower MPG. The higher the ethanol content the more impact to MPG.

    The Prius manual states not to use higher than E15 (Gen 4 pg 737, Specifications). Most likely because the injectors and fuel pump are not capable of providing enough fuel to maintain stoich even at maximum flow rate. Other reasons are that ethanol can reek havoc on fuel system components not designed for it.

    E85, even though it has less BTU per unit of volume than 100% gasoline, is used by tuners/modders as a "poor man's race fuel" due to the gasoline having >100 octane rating. But that's a discussion that requires many cold beverages.
     
    #196 Weasle543, Apr 17, 2016
    Last edited: Apr 17, 2016
  17. alfon

    alfon Senior Member

    Joined:
    May 17, 2009
    1,370
    270
    0
    Location:
    seaside, oregon
    Vehicle:
    2010 Prius
    Model:
    III
    I believe all new gasoline cars have components in the fuel system that is safe for ethanol. I have heard of some Volt owners using a
    30% blend of Ethanol with no problems or engine light activation.

    I also had a 1994 Civic VX, the rare one, EPA rated at the time 55 MPG hwy, I only had to replace to O2 sensor once under warranty. This was a dependable car, 45-50 mpg real world, and lasted over 300,000 miles and nearly our entire family used it during its life....
     
  18. DieselHybrid

    DieselHybrid Junior Member

    Joined:
    Apr 7, 2012
    36
    10
    0
    Location:
    Mid-Atlantic
    Vehicle:
    2016 Prius
    Model:
    Two
    Not much driving during my (2 Eco); only 482.4 miles / 8.91 gallons = 54.14mpg

    As suspected, no change in mileage after installing 16x6.5 Motegi Traklites with Michelin Energy Saver 195-60-16. Recall that this aftermarket tire/wheel configuration is ~8lbs of rotating mass per corner, or ~32lbs total. Lost weight where it counts most- lighter than the stock 15" tire/wheel - however at highway speeds the more porous 5-spoke Traklites are perhaps less aero than the disc-like oem plastic wheel covers.
     
  19. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,066
    15,372
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    I did this experiment on our 2003 and 2010 a while back:
    • Up to E50 - no problem other than the ethanol effects on MPG
    • Above E50 - check engine light and a fuel trim fault
    • E85 - works fine except on cool morning, ~40F, when the engine can stall on first start
    Unfortunately the retail price of E85 does not make anything above E10 worthwhile.

    Bob Wilson
     
  20. Surferboy

    Surferboy Junior Member

    Joined:
    Feb 3, 2016
    14
    23
    0
    Location:
    Los Angeles
    Vehicle:
    2016 Prius
    Model:
    Four
    4th fill up. Best mileage yet! :)
    575 miles. 10.1 gallons. 56.9 MPG calculated. Display 59 MPG.