6 speed speedo stuff

[JoshH]

So I was sitting here today just playing around with EFI Live. I decided to take a look at the "Speedo" tab. I opened up the paramaters and noticed the following:

{H0101} Vehicle Speed Sensor Pulses per Mile:4000
{H0103} Final Drive Ratio: 4.10
{H0104} Trans Output Shaft Revs/Mile: 423
{H0136} Tire Revolutions Per Mile: 682
{D5061} Transfer Case Ratio: 2.7

I know some of this stuff is wrong, like the final drive ratio, but that isn't what's bothering me. The thing that bothers me is the fact that these numbers don't even make sense with each other. I'm going to have to make some assumptions on what these things mean. That may be part of what's leading to my confusion, but I doubt it.

Of course H0136, H0104 and D5061 are self explanatory, but the other two I can only make a faily well educated guess on what they mean. I'm guessing H0101 is the total number of times a tooth passes by the VSS during one mile of travel. I'm also guessing that H0104 is the total number of revolutions the output shaft (I'm forced to assume the output shaft is the shaft coming out of the back of the transmission that the driveshaft, 2wd, or transfer case, 4wd, hooks up to) would make during one mile of travel.

Using those obvious values and the assumed meanings we should be able to divide H0101 by H0104 and come up with the total number of teeth on the speed sensor "wheel", or whatever it's called. Unfortunately it doesn't quite work out right. If you divide H0101 (4000) by H0104 (423) you come up with 9.456. I don't quite see how you can have a fraction of a tooth. It doesn't make much sense to me, but it gets even stranger. If you were to take H0136 and multiply it by H0103 you should come up with the total number of revolutions the driveshaft makes in one mile of travel which, according to the assumptions I've made, should be the same as H0104. So if you do the math you come up with 2796.2, but that is no where near the value of H0104 (423).

Does anyone know what is going on with this table? The reason I'd like to get it figure out is because I'd like to tune my shifting, but I noticed the shift speeds in my stock programming are not even close to being accurate. For instance, my WOT 2-3 shift speed is set stock at 32 mph, but it doesn't actually occur until closer to 45. I think it is being thrown off by the inaccuracies in this table, but I don't know how to adjust it.

I am thoroughly confused. Can anyone shed some light on this for me?

[Blacky]

Welcome to my nightmare... nothing is as it seems.
You are right to ask these questions, I am still working on the answers... Feel free to chime in with anything that sounds reasonable.

Regards
Paul

[JoshH]

Well, at least I know you're working on it. Hopefully you can get it figured out without too much trouble.

[Cougar281]

The speed sensor has a different number of pulses per rev than what would normally be used by GM, so the ECM has 3.73's programmed in for the final drive ratio, but the TCM has 4.10 programmed in to "massage" the signal to th ECM so it thinks the speed sensor has the expected number of pulses per revolution.

[Donovan]

Paul,

Any update on how these values interoperate?

[Donovan]

So I changed the speedo calibration (h1036) independantly to 570 (37" tires) and have not noticed any significant difference. It still seems to shift at speeds much ealier than stated in the shift speed tables.

Has anyone changed the TOS or any of the other 6 speed calibrations with any luck? I read on the diesel place that someone changed the VSS revolutions per mile (h0101) to something the speedo calc came up with and the tranny "stack shifted" and was close to breaking something so I am holding off on that until the EFI guys have some more info for us....

[dynarex]

i know i had to change the ecm and the tcm tire revs table to get a result

[Donovan]

i know i had to change the ecm and the tcm tire revs table to get a result

I did change the speedo calibration in both the TCM and ECM. In some testing I have noticed that the ABS isn't working now as I can lockup tires.... Also after I reset the taps with a PPE tuner, The tranny is engaging reverse kindof rough. Not sure if that stuff is related, but I suspect that it is. I think as a next step I am going to go back to the stock speedo configuration and try changing the shift points.

[Tecks]

did anyone figure this out yet. I just changed the ECM did not think of the TCM. Seem to be different but haven't got check it out yet w/ wifes sub.