Hobbit's RPM hack

Discussion in 'Gen 2 Prius Accessories & Modifications' started by FirstFlight, Mar 28, 2011.

  1. FirstFlight

    FirstFlight Member

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    I have my Fluke DMM hooked up to pin #23 and chassis ground.

    When the engine was on (idle) I got about 50Hz. It would fluctuate a lot and seemed to increase as I pressed the gas but it didn't seem to be linear and certainly not respective of the actual engine RPM.

    I was able to get the squirt hack working but the RPM one I wasn't successful with.

    Can someone guide me in the right direction?
     
  2. ken1784

    ken1784 SuperMID designer

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    I would suggest you to subscribe the techinfo.toyota.com site (starting US$15/2-days) for obtaining wiring diagrams, repair manuals and others.

    [email protected]
     
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  3. FirstFlight

    FirstFlight Member

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    I have the schematics. I can see where the IGF wire goes to and from. I can measure frequency. My only issue is that the value doesn't seem to be correct. I seems too low.

    For example, at idle, I'm measuring about 50 Hz. When I multiply this by four, that's only 200Hz or 200 RPM. Wouldn't a DMM be the most accurate tool to measure frequency?
     
  4. ken1784

    ken1784 SuperMID designer

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    200Hz (pulse per second) means 1200 revolution per minutes.

    [email protected]
     
  5. FirstFlight

    FirstFlight Member

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    Yes, I'm an idiot. The engine speed is rpM, not rpS! Thanks for helping me on that.

    But, how did you come up with 200Hz = 1200 RPM? Wouldn't that be 12,000 not 1200?
     
  6. ken1784

    ken1784 SuperMID designer

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    Oh, my bad...
    I think you should observe 80Hz @ 1200rpm.
    (80/4) X 60 = 1200

    [email protected]
     
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  7. FirstFlight

    FirstFlight Member

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    Ahhhh, you just turned my light bulb on! ........in a non-sexual way of course.....haha!

    I was multiplying by 4! So yeah, I was seeing about 50Hz, which is about 750 RPM at idle. That seems about right!

    Now I just have to hook it back up to my PIC and redo the math and I should be good! Thanks for the help Ken!
     
  8. ken1784

    ken1784 SuperMID designer

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  9. FirstFlight

    FirstFlight Member

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    50 Hz X 60 = 3000

    3000/4 = 750

    My confusion was that I was multiplying the IGF pulses by 4 when I should have been dividing by 4.
     
  10. ken1784

    ken1784 SuperMID designer

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    Anyway...
    On highway driving (above 42mph), you should observe approx 1000rpm when it is fuel-cut mode (accelerator off), and you should observe approx 1300rpm on the minimum power demand.

    Please do calibration of your tacho-meter using above known rpm numbers.

    [email protected]

    [​IMG]
     
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  11. FirstFlight

    FirstFlight Member

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    I checked this last night. I need to condition the signal a bit through software or by using a capacitor but I see between 980 - 1040 RPM in SHM and when the Prius is in regen (above 41, gas not pushed), I see between 1200 and 1400 RPM(my value jumps a lot)

    At idle, with the engine warmed up, I see about 800 RPM, give or take 100 RPM.

    Do these numbers seem about right?
     
  12. ken1784

    ken1784 SuperMID designer

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    These numbers are same as my observation.
    My observed warming up number is between 1200-1350 rpm.
    I have never seen below 950 rpm when engine was running.

    [email protected]
     
  13. 2009Prius

    2009Prius A Wimpy DIYer

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    Here is a record of RPM, speed, and HV current from this morning that agrees well with Ken's numbers:

    [​IMG]
     
  14. FirstFlight

    FirstFlight Member

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    Cool graph. What did you use to get that data?
     
  15. 2009Prius

    2009Prius A Wimpy DIYer

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  16. cproaudio

    cproaudio Speedlock Overrider

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    Another reason to install a carputer
     
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