Can not change H0104 in TCM. Need help correcting speedometer on 4500.

[WI Huck]

I am working on a 2005 Kodiac 4500. We are trying to correct the speedometer for tires that measure 41.25 from the top of the tire to the ground. In the engine tune we can change H0101, but it does not correct the speedometer. So next we went into the TCM and we see H0101speed sensor pulses per mile, H0103 final drive ratio, H0104 trans output shaft revs/mile, H0136 tire revolutions per mile. I matched up H0101 in the TCM to the same number in the ECM (100328 ). Next I changed the H0103 from 4.10 to the actual 5.13. (We tried it both with 4.10 and the 5.13.) Then I try to change the H0104 to what the calculator tells me it should be (2508 ). I can put the number in but every time I arrow down to the next box or try to save it will automatically change the value back to 1024. I tried the calculator Apply and everything else I could think of. When we drive the truck with what does save it will not shift out of first.

We could not correct the speedometer with engine tune changes alone.

Thanks for your ideas.

Mark

[WI Huck]

The tire size now is 41.25 and was 32.25 stock. First I tried to use the numbers that the “Speedometer Calculator” gave me without any luck. Those numbers appeared to be off so I tried to figure out the difference in a percentage. From the stock tire size to the new tire size I came up with a .7818 multiplier. I used that multiplier in the TCM in the Speedo file times the number that was there on the stock tune. I changed the following numbers one by one without seeing a change in the factory speedometer compared to a GPS unit; H0136 Tire Revolutions per Mile, H0104 Trans Output Shaft Revs per Mile, and H0101 Vehicle Speed Sensor Pulses per Mile.

I first tried to correct the speedometer In the ECM tune. The only option there was the H0101 Vehicle Speed Sensor Pulses per Mile file. I made all kinds of changes to the ECM H0101 and did not see a difference. That is why we started to mess with the TCM.

No matter what we change it appears to be close to 10 MPH off at 30. The only thing that made a noticeable difference in the way the truck ran was changing the gear ratio in the TCM from 4.10 to 5.13. It was not a positive change.

[WI Huck]

I can not figure out what the factory speedometer uses to calculate the MPH in a 4500.

[Toired Old Man]

I can not figure out what the factory speedometer uses to calculate the MPH in a 4500.
It seems as though EFI doesn't understand the DECIMAL System, everything must be in metric to change the speedo system calibration