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Thread: 6.7 PSD Downshift Pedal Postion

  1. #1
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    6.7 PSD Downshift Pedal Postion

    Can someone help me understand the logic for the Downshift Shift Scheduling? I have lowered the MPH in these tables for all 6 gears but it doesn't seem to make a difference in where the truck will downshift in relation to speed and pedal position. Also the "pedal position" Doesn't seem to make very much sense, nothing I can log in the scanner will give me ADC for the pedal.

  2. #2
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    Quote Originally Posted by Kadams87 View Post
    Can someone help me understand the logic for the Downshift Shift Scheduling? I have lowered the MPH in these tables for all 6 gears but it doesn't seem to make a difference in where the truck will downshift in relation to speed and pedal position. Also the "pedal position" Doesn't seem to make very much sense, nothing I can log in the scanner will give me ADC for the pedal.
    How did you lower the MPH? The table is in OSS, Thus you'd want to raise the OSS for it to downshift sooner not lower it. And depending on tire size and rear gear ratio that will change the actual MPH at which this downshift occurs. To make a change using the table you'd take the gear ratio for the gear it's going into so say on the 2-1 downshift take first gears ratio, multiply it by OSS to get desired engine RPM. Or i like to work the other way, take the engine RPM you'd want it to downshift at, let's say we want it to downshift at 1800 engine rpm take that divided by the gear ratio, so for first gear it's 3.97 and that nets you a OSS of 453.4rpm and insert that OSS in your table at the desired throttle position you want it to occur at. The factory table won't let it downshift into first unless it's below 212 OSS. You also have to look at the downshift prevention table as it limits the max allowed engine RPM after a downshift.
    Last edited by JaegerWrenching; 08-06-2019 at 10:58 PM.

  3. #3
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    Quote Originally Posted by JaegerWrenching View Post
    How did you lower the MPH? The table is in OSS, Thus you'd want to raise the OSS for it to downshift sooner not lower it. And depending on tire size and rear gear ratio that will change the actual MPH at which this downshift occurs. To make a change using the table you'd take the gear ratio for the gear it's going into so say on the 2-1 downshift take first gears ratio, multiply it by OSS to get desired engine RPM. Or i like to work the other way, take the engine RPM you'd want it to downshift at, let's say we want it to downshift at 1800 engine rpm take that divided by the gear ratio, so for first gear it's 3.97 and that nets you a OSS of 453.4rpm and insert that OSS in your table at the desired throttle position you want it to occur at. The factory table won't let it downshift into first unless it's below 212 OSS. You also have to look at the downshift prevention table as it limits the max allowed engine RPM after a downshift.
    I figured it out, I wasn't thinking when I made the post. The next day I looked at it and realized what I had done. Raised the MPH and got what I wanted. The 12 I was working on did not use OSS for the Shit scheduling, it uses MPH. Thanks for the reply. NON VGT Cab and Chassis was a trick making something with 4.88 gears actually light off without weight behind the truck but got it dialed.