PDA

View Full Version : Trying to get correct VSS reading on scan tool


406nick
March 22nd, 2013, 09:23 AM
So I have all my shifts close but all changes were made without changing tire size and pulses per revolution so my vss shows only 16mph at an actual speed of about 65. Is there a way to correct this so I can get the correct speed to show up on my datalog without having to change all my shift points again? I tried using the calculator but that changed it too drastically. My current revs are at 40 and when I change to 17 (or even 16) the speed shows close to actual speed but the transmission doesn't shift. Any ideas?
EagleMark
March 22nd, 2013, 07:29 PM
You could segment swap the stock transmission back in. Then use the speedo calculator for tire and gear size, it will make the changes to all trans shift points as well. I've found if you can get tire manufacturer revolutions per mile it is way more accurate then the tire size, let EFI Live say whatever on tire height as long as RPM and gear ratio are correct.

Whys it so far off to begin with?
406nick
March 25th, 2013, 04:06 AM
I think the guy helping me was playing around and made some changes but he is not around for me to ask. Also I am very much a rookie at this and am teaching myself. So is there not a way to use the speedo calculator but leave all the shifts the same? How would I do the segment swap? Would that basically change it back to stock then I would need to go back in and change all the shifts again?
THEFERMANATOR
March 25th, 2013, 06:15 AM
Theres no segment swap in the ALLISON TCM. The TCM will not read out the correct speed as it is calibrated for 4.10 gears and 245/75/16 tires fro mthe factory. It does NOT need changed when tire size changes are made like in a gasser. IF you make ANY changes to the speedo portion for revs per mile, ALL the shift points must be MANUALLY changed.
406nick
March 26th, 2013, 02:13 AM
Well that makes sense. So it looks like I will pretty much be starting fresh if I want to be able to watch that on the datalog. How many vehicle speed sensor pulses per revolution is normal for the allison 1000? Also is there a way to figure out he percentage difference from where it is set now to what it should be?
406nick
March 26th, 2013, 02:19 AM
Oh one other question. What does the vehicle speed ratio do? It doesn't tell what it does in the description.
THEFERMANATOR
March 26th, 2013, 05:04 AM
What is this in, and what are you trying to accomplish?
beav
December 13th, 2013, 02:49 AM
Well that makes sense. So it looks like I will pretty much be starting fresh if I want to be able to watch that on the datalog. How many vehicle speed sensor pulses per revolution is normal for the allison 1000? Also is there a way to figure out he percentage difference from where it is set now to what it should be?


Oh one other question. What does the vehicle speed ratio do? It doesn't tell what it does in the description.

Good questions Nick. The ppr for the Allison output shaft should be 40. I do not know but am also very interested in what the {H0137} Vehicle Speed Ratio is and how it is incorporated into the calculations.