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Adjusting speedo (obd1 only) - noob guide from a noob for noobs

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4.9K views 2 replies 1 participant last post by  toonwarrior  
#1 ·
This is for OBD1 cars.

Tools/downloads you'll need:
OBD 1 cable - OBD Diagnostics
Flashhack - Flashhack – fbodytech
XDF file (used to understand the bin file) - EEX Definition – fbodytech
Tunerpro - TunerPro and TunerPro RT - Professional Automobile Tuning Software
Formula calculators - TC LT1 OBD1 Speedo
Laptop


1. Download the bin file
Plugin your laptop to your car via the obd1 cable, open up flashhack

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Car key has to be turned on, make sure your laptop and car don't shutdown during the process.

Click on read calibration and save that file

2. Opening the file

Create a duplicate of the bin file you just download to edit.

Open up tunerpro

Select the XDF file you would have downloaded from EEX Definition – fbodytech
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Now open up your bin file

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And under scalars look for these values
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3. Editing the file

Download and upload the spreadsheet formulas so you can edit it - TC LT1 OBD1 Speedo

Open the sheet

In the yellow fields on the left side input the values for:
-Tire width (255 for stock)
-Aspect ratio (50 for stock)
-Rim size (17 for stock)
-Rear gear ratio (3.08 for stock)
-Trans reluctor pulse freq (40 for 4l60e, 17 for t56, 12 for t56 magnum)

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Now that you have your values, go back to tunerpro

Starting with this value, I've updated to 17 in the case for a t56 setup
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Copied the value from the spreadsheet on the speedo scalar into the base
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#2 ·
For the speedo scalar - scan tool value copy the value from speedo scalar - scan tool in the spreadsheet
Which is 50.97 in my case
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You can also calculate this value with the formula: value = ( gear ratio * tire revs per mile ) / 60

For the final value for the divisor copy the scalar fraction value from the spreadsheet into it.
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You can also calculate this value by the formula: value = 4000 / (ppm / speedometer scaler - base)

Now save the updated file as your edited one

Once you save the file make sure the values actually get saved, you might have to edit it one by one to save.

Now connect your laptop back to your car and upload the bin file.

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Take a test drive, get out a gps, if your gps values are inline with your car you are good.

If not get the difference between the gps and car at certain speeds and use the values in the right side of the spreadsheet to dig down and update the bin file with the generated values.

200674
 
#3 ·
For future reference

If you are purchasing a tune from someone like Bryan herter they maybe using a revision B calibration, this will not work with XDF definition found on flashhack (EEX file).

You will need the EEB definition file, can't upload it here but it's out there on another forum I forget which.
 
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