Weird cruise control / mpg issue.

Discussion in 'Gen 2 Prius Main Forum' started by Prius92, Sep 4, 2022.

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  1. Prius92

    Prius92 Active Member

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    I've had poor MPG for months. Tried all kinds of stuff. New spark plugs, air filter, new cat and all new o2 sensors, 2 of the injectors are brand new. Cleaned MAF, etc.
    No codes. Rebuilding the hybrid pack didn't help (but did help the battery itself a ton).

    I drove it an hour today, and noticed a couple things.
    1. With CC on, the engine never shuts off, even downhill. This seems to cause the excess gas consumption.

    If I operate it normally, the engine shuts off downhill.

    2. When I give it a little gas, and let go of the throttle (this is with the CC off), the car seems to slow down a bit more than normal, you can even feel the body shift downward slightly.

    It's like the regen brakes are applying a little harder than normal, but the 1st issue is the most concerning. Battery disconnect for 30 minutes does not fix the issue.
     
    #1 Prius92, Sep 4, 2022
  2. Tombukt2

    Tombukt2 Senior Member

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    And there's no lights on on the dash nothing. Very strange
     
    #2 Tombukt2, Sep 4, 2022
  3. Prius92

    Prius92 Active Member

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    The only thing I can think of is when I cleaned the throttle body I had to adjust the TPS, maybe the CC uses a different reference of throttle position?
     
    #3 Prius92, Sep 4, 2022
  4. Tombukt2

    Tombukt2 Senior Member

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    That could be but I would think just adjusting the TPS the little bit that you can The computers would make up for the rest of it or show the cruise what it needs to see so I guess you use the cruise a lot I don't much. I'll have to try this tomorrow
     
    #4 Tombukt2, Sep 4, 2022
  5. dolj

    dolj Senior Member

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    Interesting, I didn't think the TPS was supposed to be adjusted in the field.

    And, why did you have to adjust it?
     
    #5 dolj, Sep 4, 2022
  6. Another

    Another Senior Member

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    I use CC a lot. It really helps on mpg. I don’t drive in mountains though.

    One thing I’ve noticed is that if I’m in CC mode and the engine is on with power also coming from battery, and the battery is pretty full, if I momentarily that is for a second or two, disengage the CC with the lever then restart the CC, the engine turns off and the car goes full EV mode and the engine stays off. Seems like a software glitch.
     
    #6 Another, Sep 4, 2022
  7. TMR-JWAP

    TMR-JWAP Senior Member

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    Any chance you have the car in "B" instead of "D"?
     
    #7 TMR-JWAP, Sep 4, 2022
    Tombukt2 likes this.
  8. Tombukt2

    Tombukt2 Senior Member

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    That's really good call actually
     
    #8 Tombukt2, Sep 4, 2022
  9. Prius92

    Prius92 Active Member

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    I took apart the entire throttle body and cleaned the bare metal parts in an ultrasonic cleaner. I didn't want to get the TPS in any liquids.

    The thing I don't get...why is there even an adjustment on this? Every other brand of car I've ever worked on doesn't have adjustment on the TPS. You can't adjust it "in field" either.
     
    #9 Prius92, Sep 4, 2022
  10. fuzzy1

    fuzzy1 Senior Member

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    CC is supposed to work only in D. B cancels CC.

    Though when I'm using CC downhill, the ICE generally doesn't stop either, but spins up in engine braking mode. But this strongly depends on slopes and speeds.
     
    #10 fuzzy1, Sep 4, 2022
  11. Prius92

    Prius92 Active Member

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    Had window down trying to get this new Techstream cable working, have to roll back my old laptop from Win 10 to 7.
    But noticed when idling, it runs very rich. The smell of gas is almost nauseating.
    No codes for it. Was running somewhat rich before I did anything with battery, cat converter, o2 sensors, etc.
    What would cause it to run rich when in ready mode and cycling on to charge battery?
    If I have a bad vacuum hose, could that cause it?
     
    #11 Prius92, Sep 4, 2022
  12. Tombukt2

    Tombukt2 Senior Member

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    Bad vacuum noise could cause a whole lot of nonsense you need to definitely find out why that is A lot of sucking noises is not good and supposed to be sucking on something and you're not really supposed to hear it so that could make idle go up etc and then the computer's trying to compensate for that and oh God it sounds like a real circus.
     
    #12 Tombukt2, Sep 4, 2022
  13. Tombukt2

    Tombukt2 Senior Member

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    In my early celiacs I think we had adjustment on TPS very small scale. Played with it once put it right back.
     
    #13 Tombukt2, Sep 4, 2022
  14. Prius92

    Prius92 Active Member

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    Just went to town and it ran fine. It seems the rough idle and running rich only happens until the engine is warmed up.
     
    #14 Prius92, Sep 4, 2022
  15. dolj

    dolj Senior Member

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    That is probably way overkill. You only really need to remove the filter housing and the MAF sensor then clean the throttle body throat and throttle plate with some throttle body cleaner and a soft brush followed by a wipe with a cotton cloth. No need to disassemble more than that.
    It is for getting the TPS adjusted at the factory. It is not supposed to be messed with after that.
    If by that you mean the 50 (0r so seconds of warm up (stage 1) then yeah the timing is set so the engine runs hot (and very inefficient) to warm the engine quickly. While that is happening the car, if driven, will predominantly use the electric motors for propulsion.
     
    #15 dolj, Sep 4, 2022
    Last edited: Sep 4, 2022
  16. Prius92

    Prius92 Active Member

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    Isn't that bad on the entire engine including the spark plugs? I thought the coolant storage tank was supposed to be used for warning things up.
     
    #16 Prius92, Sep 4, 2022
  17. Tombukt2

    Tombukt2 Senior Member

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    It's just for a very short time and then whenever the timing gets back normal the plug self clean and all this and that kind of nonsense in a normal internal combustion engine anyway I would hope in the one N z still. Not sure about the Gen 3 and it's Atkinson cycle business it seems to run on its own puke regurgitating that puke and still running.
     
    #17 Tombukt2, Sep 4, 2022
  18. Prius92

    Prius92 Active Member

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    Did some more checking. It's not the CC.
    Ran it at 61MPH for 9 miles, got 54MPG, went again on same stretch of road, ran it at 70MPH, only got 38MPG.

    How can a speed increase of only 9MPH cause a 29.6% decrease in MPG? Obviously speed increases will hinder MPG, but this badly?
     
    #18 Prius92, Sep 4, 2022
  19. dolj

    dolj Senior Member

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    Drag increases exponentially for each mile-per-hour increase.

    Redo the experiment at 55 MPH for a more impressive MPG. The sweet spot for the Gen 2 is somewhere around there.
     
    #19 dolj, Sep 4, 2022
  20. Prius92

    Prius92 Active Member

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    Most of the highways around here are 65MPH 4 lanes. You'll get ran over if you don't go at least 70, which would technically be 72 in my car as my speedometer is off. (Not sure why, oem tire size/wheels).

    Like I said, I know MPG goes down with speed increases, but I've never seen it this bad in a car, and I thought the Prius was supposed to have an insanely low drag coefficient?
     
    #20 Prius92, Sep 4, 2022
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