Low speed throttle control

Discussion in 'Fuel Economy' started by Gageraid, Dec 11, 2014.

  1. Gageraid

    Gageraid Well-Known Member

    In my vehicle, 1st and 2nd gear (automatic) are extremely sensitive to increase and decrease in throttle at slow speeds (0-20mph). If you let off the throttle completely in those gears you can feel it in the seat of your pants so to speak.
    My question is, is letting off the throttle in these gears very good for mpg, good, or bad if I know I will have to increase speeds in the near future? A good example would be something like when you can see a traffic light or stop sign in the distance. If I let go completely it slows down pretty fast, and even faster in 1st and 2nd gear.
    2008 Jeep Liberty, 4 speed automatic, and 3.7L engine.
     
  2. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Neutral and coast to the light. Or shift it down to 2 for engine braking with fuel cut if you're coming in too fast and need to slow down.
     
  3. Gageraid

    Gageraid Well-Known Member

    I'd rather coast in gear in this vehicle. I never thought about shifting down into 2, so I'll keep that in mind. I used to do this all the time is my last vehicle which was a 70's muscle car that was curbereted and a 3 speed auto.
    Also, I see you briefly mentioned fuel cut, but does shifting down manually like this force fuel cut scenario for the ecu? If so, that's neat.
     
  4. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    I can't say for sure for your car, but for Hondas if it's engine braking above 1100 rpm it will go into fuel cut mode. Downshifting as you slow can maintain it longer. I can feel a "surge" when the fuel comes back on, like the engine braking is releasing and letting the car roll more freely.
     
  5. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    In my Honda 5AT , you cannot always get fuel cut when you want it. If you have been feathering the throttle and slowly back off, you will coast like the old-timey auto trans cars did. If you take your foot off the gas quickly , you can get fuel cut. That's the best I can explain it. Obviously, a manual trans car could react differently.

    The first time my #1 daughter drove this car , she was amazed how the car would slow down in fuel cut while downshifting on its own accord.
     
  6. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Huh. In my 2004 5AT Odyssey, if you let off the gas pedal, you're in fuel cut engine braking. Period. Every single time. So I do a LOT of shifting into neutral and back to drive.
     
  7. Gageraid

    Gageraid Well-Known Member

    Okay, how about this other question that is related.
    I've been wondering how aggressive or lightly I should take my foot off the throttle. I've tried both ways, but not sure what the difference is. Maybe I can check with my Scangauge?
    Also, I've been driving blind for a few weeks since I have the Progressive Snapshot in my OBDll port. Can't wait to get my gauges back.
     
  8. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    The thing to watch on the Scangauge is Open/Closed Loop. Open means it's in DFCO. Closed means it's reading the exhaust O2 sensor and adjusting the fuel mix based on the feedback loop to keep it at the ideal mix, not rich or lean. Open loop means it's ignoring that sensor. If there's no fuel being used, there's no need to read the result and adjust the mix.
     
  9. litesong

    litesong litesong

    My own 2013 6sp. auto Elantra(bad-mouthed for poor mpg) is overall averaging 39mpg, when most people are averaging 30mpg or less. The Elantra low 131 lbs-ft of torque, when featherfooted, really helps the smoothness, unlike my wife's 2008 Hyundai Accent manual shifter, which is very throttle abrupt at crawling speeds. The shift points of the Elantra are set very low, also helping smoothness & you can drop into 5th gear by 30mph. Altho NOT as wonderful as a CVT, the auto Elantra seems to be good in stop & go traffic, modulating very nicely. Tho not in heavy traffic often, my mpg readout, seems to be quite high if, at its slowest speeds, I can keep from stopping completely. However, if people are impatient with the 131lb-ft of torque & low speed gear shifts, & push the car harder & hard, mpg will go away quickly.
     
    Last edited: Mar 31, 2015

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