Colorado speedometer won't correct.

[TheBac]

Ive got 265/70r17 tires on the Colorado. Stock is 255/65r17.
Speedo has been low 4-5mph @ 70mph since I bought truck.
Using my go-to internet tire compare site, 255 circumference is 2398mm, 265 is 2520mm
Downloaded the tune into EFI to change speedometer parameters.
H0122 (axle ratio) is 3.42 -- correct, no change.
Changed H0139 (driven wheel circumference), and H0140 (non-driven wheel circumference) to 2520.
H0105 (EM pulses per kilometer output rate) left alone at 430
Loaded tune back into truck.
No change in speedometer.

What did I miss?

 

[Lennydmaxguy]

I'm not sure why that wouldn't work, but I can say from my experience that changing H0105 corrects the speedometer.

 

[TheBac]

So I have to recalculate pulses per km? Is there a calculator for that?

 

[Lennydmaxguy]

Yes, the V8 editor has a built in calculator. Since you know the MPH change you need, I would go to the Speedo Fine Tuning tab, enter your values, and then multiply H0105 by the correction value given.

 

[TheBac]

OK thanks. I prefer to use 7.5, but -gulp- will try 8.

 

[TheBac]

Man, 8 is just not intuitive or user friendly.
Finally found the calculator, and it gave me a multiplier of .945946. Multiply 430 x .945946 = 406.75. I just rounded down to 406. Will attempt to upload that tomorrow and see what happens.

Thanks for the assist, Len. Much appreciated.

 

[TheBac]

Dug the V2 out of its hiding place, loaded the revised tune into the truck and went for a drive.....SUCCESS! 40mph is 40mph!

Thanks Len!!!

 

[Lennydmaxguy]

Any time