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Calibrating the speedometer with CAT E.T.

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Diesel Dave, Oct 2, 2015.

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  1. Oct 2, 2015 #1
    Diesel Dave

    Diesel Dave Last Few of the OUTLAWS

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    The equation I'm using is the "tire rotation per mile" (473) for my kellys tall rubber multiplied by "rear end ratio" (3:36) and multiply by "16". That gives me the ppm to program the ECM. I found this on google but its not working correctly. Is there another equation or formula available ? My set up, RTO 15613 final drive .87, with DS 402 ratio 3:36 on 11:24.5 Kelly's KDA drive tires. The truck was originally came equip with low pro's, so its been off about 3 to 4 mph.
    EDIT: Let me add, I am getting in the ECM with the passwords and all, its just the number's I put in are not giving me the correct mile an hour. I came up with 25428 ppm, and its 5 miles an hour off.
     
    Last edited: Oct 2, 2015
    Reason for edit: edit
    Diesel Dave, Oct 2, 2015
    Diesel Dave, Oct 2, 2015
    #1
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  3. Oct 3, 2015 #2
    GrapeApe

    GrapeApe Road Train Member

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    That is the correct formula. Double check your tire revs per mile. If the 473 came from Kelly specs, it should be close, but I've seen them off before. Many tires have been redesigned with less tread depth for less rolling resistance, but sometimes they forget to update the spec manual. You can measure the tires and calculate rotations per mile to double check.
     
    GrapeApe, Oct 3, 2015
    GrapeApe, Oct 3, 2015
    #2
  4. Oct 3, 2015 #3
    T800H

    T800H Medium Load Member

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    Dave, I check the circumference on my 24.5 tall tires and it came to just under 470 rpm.
     
    T800H, Oct 3, 2015
    T800H, Oct 3, 2015
    #3
  5. Oct 3, 2015 #4
    KVB

    KVB Heavy Load Member

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    What is the reading in et? Do you get the same 5 mph difference, or only in the speedometer?

    Don't know your truck, but does speedometer get signal from engine ECU or is it hooked up directly to sensor in transmission?
     
    KVB, Oct 3, 2015
    KVB, Oct 3, 2015
    #4
  7. Oct 6, 2015 #5
    Diesel Dave

    Diesel Dave Last Few of the OUTLAWS

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    I'm getting 5 mph off according to my Garmin gps and including the mileage is off. Someone mention about the speedo head, it has some keys in back it adjust, so I checked mine and it does have them, so now I have to figure out if someone prior calibrated it that way or not. I don't want to mess with something I'm not familiar with.
     
    Diesel Dave, Oct 6, 2015
    Diesel Dave, Oct 6, 2015
    #5
  8. Oct 6, 2015 #6
    T800H

    T800H Medium Load Member

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    there is a formula to calibrate from the back keys, I know there was a thread a few years a go about that and it was very simple, see if you can find that thread Dave.

    I'm not sure if it was here or the other site, but almost positive it was here.
     
    T800H, Oct 6, 2015
    T800H, Oct 6, 2015
    #6
    Diesel Dave Thanks this.
  9. Oct 6, 2015 #7
    Diesel Dave

    Diesel Dave Last Few of the OUTLAWS

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    I do recall running into a forum regarding the keys on the back of the speedo head but it was for a mechanical if my memory serves me right.
     
    Diesel Dave, Oct 6, 2015
    Diesel Dave, Oct 6, 2015
    #7
  10. Oct 6, 2015 #8
    lester

    lester Midwest's #1 Feed Hauler

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    Dip switches I call them. I changed speedo a while back, called my dealer with tire size rear ratio and trans ratio they told me how to set them.
    01 pete
     
    lester, Oct 6, 2015
    lester, Oct 6, 2015
    #8
  11. Oct 7, 2015 #9
    GrapeApe

    GrapeApe Road Train Member

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    That's how you do it if your speedo is driven directly from the sensor. If the ECM drives the speedo, the dip switches stay put and you adjust with the engine software.

    The easiest way to tell is if your tail shaft sensor has 2 plugs (4 wires) and both are plugged in, 1 is for the speedo and the other is for the ECM. In that case you need to adjust the dip switches. If you have 1 plug (or only 1 is used), then that goes to the ECM and you need to change the ECM parameter to adjust the speedo. But you should get the correct DIP switch settings from the dealer, just in case someone changed them in the past.

    Well, there is a 3rd scenario (not the case here), 1 plug and a mechanical engine (no ECM), in that case, the dip switches need to be adjusted. But we know it's got an ECM in this case.
     
    GrapeApe, Oct 7, 2015
    GrapeApe, Oct 7, 2015
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    Diesel Dave Thanks this.
  12. Oct 7, 2015 #10
    ROBSREDFORD

    ROBSREDFORD Light Load Member

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    Dave chances are your forty pin truck still uses dip switches. The ecm ppm is probably real close to accurate with the formula you used.....so your ecm should be tracking miles Correctly....I used to have book to set dip switches but if in bind call Dixxon or dickson who made the gauges and they can help u fine tune to get mechanical odometer/speedometer closer
     
    ROBSREDFORD, Oct 7, 2015
    ROBSREDFORD, Oct 7, 2015
    #10
    Diesel Dave Thanks this.
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