Bud's '97 80 series speedometer correction project (1 Viewer)

[Bud_Dude]

So due to larger tires and regearing my speedo is off by 10% or so and I'm tired of doing the math in my head while rolling down the highway.
Lots of people use the venerable Yellow Box to correct their speedometer after regearing and bigger tires.
Official home page of the Yellow Box Speedo Recalibrator
There have been reports of this unit causing some issues with the cruise control due to the lag in its corrected speed output.

But, has anyone tried the Dakota Digital SGI-100BT for their speedometer correction project?
SGI-100BT: Universal Speedometer and Tachometer Interface

Dakota Digital Accessories

You’ve purchased Bluetooth-enabled Dakota Digital accessories and want to get the most out them, all with wireless control? The Dakota Digital Accessories App allows you to do just that! When using the SGI-100BT --------------------------- -Speedometer and/or Tachometer input and output...

apps.apple.com

This looks to be a far more advanced unit than the Yellow Box that most folks use and allows calibration adjustment with onboard pushbuttons like the Yellow Box, but also with an IOS (iPhone) or Android device via Bluetooth. Meaning one can install the module behind or under the dash and recalibrate at will without need to actually get to it. It also seems very reasonably priced at around $94 on Amazon...

So I've ordered one of the Dakota Digital units and will install it in the next week here. In preparation to install it I've studied the signals from the speed sensor and confirmed couple things I've not found documented elsewhere here on IH8Mud... Hopefully others will find it useful.

1. The number of pulses per mile (PPM) from my '97 80 series LC - For this I put the truck up on jack stands and ran the truck for two miles as indicated on the odometer trip meter and recorded a total of 8198 pulses for an average of about 4100 pulses per mile as measured with a Universal Counter.
   
   
   
   
2. The nature of the signal into the speedometer as viewed with an oscilloscope - A very clean square wave 11.5V signal with a period of approximately 60mS at an indicated speedometer speed of about 15mph.
   
   
   
   
3. For purposes of connecting the unit I'll be cutting the red-orange wire on pin-1 of the IH1 connector behind the glove box to insert the Dakota Digital speed calibrator. (a minor issue will be determining which side of the wire goes to the sensor and which goes to the speedo... )
   
   
   
   
   
   

More to follow as this project moves forward here.

 

[Overlandeffex]

Super interested in how this turns out!!

 

[Bud_Dude]

So due to larger tires and regearing my speedo is off by 10% or so and I'm tired of doing the math in my head while rolling down the highway.
Lots of people use the venerable Yellow Box to correct their speedometer after regearing and bigger tires.
Official home page of the Yellow Box Speedo Recalibrator
There have been reports of this unit causing some issues with the cruise control due to the lag in its corrected speed output.

But, has anyone tried the Dakota Digital SGI-100BT for their speedometer correction project?
SGI-100BT: Universal Speedometer and Tachometer Interface

Dakota Digital Accessories

You’ve purchased Bluetooth-enabled Dakota Digital accessories and want to get the most out them, all with wireless control? The Dakota Digital Accessories App allows you to do just that! When using the SGI-100BT --------------------------- -Speedometer and/or Tachometer input and output...

apps.apple.com

This looks to be a far more advanced unit than the Yellow Box that most folks use and allows calibration adjustment with onboard pushbuttons like the Yellow Box, but also with an IOS (iPhone) or Android device via Bluetooth. Meaning one can install the module behind or under the dash and recalibrate at will without need to actually get to it. It also seems very reasonably priced at around $94 on Amazon...

So I've ordered one of the Dakota Digital units and will install it in the next week here. In preparation to install it I've studied the signals from the speed sensor and confirmed couple things I've not found documented elsewhere here on IH8Mud... Hopefully others will find it useful.

1. The number of pulses per mile (PPM) from my '97 80 series LC - For this I put the truck up on jack stands and ran the truck for two miles as indicated on the odometer trip meter and recorded a total of 8198 pulses for an average of about 4100 pulses per mile as measured with a Universal Counter.
   View attachment 2221264
   
2. The nature of the signal into the speedometer as viewed with an oscilloscope - A very clean square wave 11.5V signal with a period of approximately 60mS at an indicated speedometer speed of about 15mph.
   View attachment 2221265
   
3. For purposes of connecting the unit I'll be cutting the red-orange wire on pin-1 of the IH1 connector behind the glove box to insert the Dakota Digital speed calibrator. (a minor issue will be determining which side of the wire goes to the sensor and which goes to the speedo... )
   View attachment 2221266 View attachment 2221267
   View attachment 2221268

More to follow as this project moves forward here.

Thanks to @Eyedaho for his suggestion on the connector wire side question -

 

[elripster]

Much likes! I need to do something like this too.

Frank

 

[Bud_Dude]

Mission accomplished! Works great!

I knew I was about 10% off before starting and began with a setting of 0.900, after a few miles on the highway at various speeds I was still reading a bit high so I nudged the correction a little more on the shoulder of the road and repeated the test. My ultimate correction ratio was 0.890 or -11% for my ~34" tires and 4.88 gears. Tested over a wide range of speeds from about 25 to 75mph and all read within +/-1mph of my iPhone GPS speedometer app.

In addition, it works perfectly fine with my cruise control!! No hunting or drifting in the speed. I tested the unit on the bench in my shop beforehand and could see that there was negligible lag or delay in the output frequency following a change to the input frequency.

Installation wise, see initial comments in previous posts -
I started by creating a small wiring harness for the unit to connect to connector IH-1 located behind the glove box. That connector is behind other items like the HVAC control 'amplifier' which needs to be removed to get to the connector. In building my wiring harness I used what looked like some decent, but very inexpensive, "MUYI" four pin automotive connectors (allegedly waterproof) that I found on Amazon... I would not buy or use them again, just too difficult to assemble and no way to disassemble them if you make a mistake. If you want a connector in your harness find a better one. As an afterthought, since I run an HF/VHF/UHF ham radio in my truck, I added a ferrite RFI filter right at the input/output terminals of the Dakota Digital module - just in case it's sensitive to RF interference.

I cut the wires at connector IH1 and spliced in 20AWG wires from my little wiring harness with non-insulated butt-splices and put heat shrink tube over the connections. To be honest, getting to that connector and cutting and splicing wires is a pretty damn difficult and frustrating. I ultimately removed the passenger seat in order to get my body farther into the truck to work at better angles. The connector really doesn't want to come out and make itself more accessible. Perhaps alternative wire splicing / connection methods would have been easier, but I feel the method I used should survive vibration and shocks experienced offroad; time will tell.

The Dakota Digital module ended up behind that factory audio system power amplifier and the ECU to the right of the glove box. I considered velcro to hold it in place, but settled on a firm piece of foam rubber wedged in above it and it's going nowhere, but is relatively easy to remove for service if needed.

Note that since the Dakota Digital module is controlled via an iPhone or Android app over Bluetooth, there's no need to physically access the unit to make adjustments. Just fire up the app, connect to the module, and adjust away. The app itself is a little funky and the correction value only shows when changing up or down, but it's easy enough to use and something that only ever gets used if you change tire size or re-gear...

 

[Overlandeffex]

I'm going to order one and come to your house to put it in!!!