I've got an 85 Z51 with a Tremec TKX swap done by the previous owner. He never got around to installing any of the new plugs or adaptors, so I've been driving it around with no speedometer for months.

Today I finally decided to tackle installing the Dakota Digital SGI-5C to make the speedometer work. With the help of some older threads about using this exact same adaptor, I tapped power and ground and intercepted the signal wire at the gauge cluster. Turned on the car and it works! The adaptor lights up and there's speed showing on the dash for the first time since I've owned it.

Here's where things get weird.

Using output 1 with all 4 switches off, the car says I'm doing 133mph when I'm actually doing 40. No big deal: I switch to output 3 per the instructions. Sure enough, this is MUCH closer, but still reads about 12 mph high. Okay, I'll just use the up/dwn buttons to tune it while the car is driving. Only they don't do anything. Pressing them repeatedly or holding them doesn't seem to have any effect. I tried flipping switch 3 to the on position, which makes the car read super slow, but the up switch doesn't work in this scenario either.

Even weirder is after I sat in my driveway with the car off for a few minutes trying to figure it all out, I suddenly couldn't get the car to start. It sort of seemed to smell really rich when this happened. I let it sit a few minutes and unplugged the battery for about 30 seconds before trying to start it again, which took 3 tries and had it running pretty rough for the first few seconds when it finally did start. It leveled out and I was able to drive it around but I'm still spooked since all I've messed with was the dash wires.

So my questions are:
1. Does anyone know how to program a Dakota Digital SGI-5 rev C or similar model?
2. Would the ECM suddenly having (inaccurate) vehicle speed data cause it to mess up the fuel mixture? Or is this maybe a completely unrelated problem?

 

I saw this thread earlier today, and there are still no responses. It has been 20 years since I calibrated a DD, I looked at the instructions to refresh my recollection. I'm not sure if this will help.

Output 3 is the one you want.
Switch 3 ON changes the calibration by 50%. Ie 4,000 Sw 3 OFF, 8,000 Sw 3 ON. If you're 12 MPH high at 40MPH that's about 30%.

Did you try Switch 4?

Lastly the up / down buttons. The way I read it, you enter "coarse" or "fine" adjustment by holding a button then turn the key to RUN. Looking at the tables, fine is really fine. You may not see any change in speedo in fine. Re-read the section for entering coarse and fine, and using the LEDs to verify what mode/status the unit is in.
Application #3 has a formula to compute the new calibration ratio. But you need to know the existing ratio. This can be done with the buttons and the key. To make it read lower, you use a lower ratio. It's simple math. True Speed / Actual Speed X current calibration ratio = New calibration ratio. I believe this is the method I used 20 years ago. More accurate and quicker too.

I have no idea how speed input could affect a failure to start. There are some calculations that use speed like deceleration fuel cut off (DEFCO) and the IAC is positioned based on speed. Hopefully it won't do that again.

You probably have it working, but here's some ideas and suggestions. Enjoy your Tremec.

 

My friend brought up a good point: I'd shut the car off to mess with the wiring on the adaptor (idk if I had to. Just seemed like the safe thing to do) but I had the battery unhooked the whole time I was wiring it up in the first place. Then as I'm driving it around trying to adjust the adapter I never get it above 40 and keep stopping and starting the engine. That's gotta confuse the hell out of a computer that's trying to put down a base map.

 

Oh that's good to know about DEFCO because without a speedometer my car would sometimes shut off when decelerating from highway speed.

I've looked at the chart in the back of the instructions but I can't really make heads or tales of it. It's got "course" "fine" "cal hi" "cal lo" and "tach". Says cal hi/lo represents switch #4 on/off. Are the numbers under course and fine the number of led flashes that the unit will show when asking it for mode? And then the numbers under cal lo/hi the multipliers that fit into the equation for new ratio?

 

That was actually the IAC control. At speed, if the throttle is closed suddenly, the ECM may not be able to open the IAC quickly enough to prevent a stall. So with road speed, the IAC is held open far enough that the stall can be prevented. That's why the idle speed seems to hang high briefly after coming to a complete stop.

Page 2 of the .pdf has the instructions for observing and changing the coarse and fine calibrations. Coarse is the UP button. RED LED flashes the Coarse setting. Fine is DOWN button. GREEN flashes the fine setting.
Determine the existing calibration.
In the table of calibrations, ignore "tach". The first two columns are the Coarse and Fine settings. Is your Switch 4 On or OFF?Then use which ever column applies for the calibration ratio.
Use the formula in Application #3 to calculate the necessary new ratio.
Find the closest matching calibration in the appropriate Sw 4 column.
While the green or red is flashing, the up and down buttons change the coarse or fine setting.

Read the instructions on page 2 until you understand how this works. You'll "get it" pretty quick. If I did, anyone can. Cheers.

 

Excellent thank you! I'll report back with my results I hope.

 

Dip switches 3 and 4 on brought the readout to about 10mph slower than gps. Then I was able to use the Up button while driving to adjust it up. Apparently it was all the way adjusted down before. Now it's dead accurate, more than my other two cars haha. Thanks for all the help!

Now I just have to figure out why my odometer isn't turning...

 

I'm curious. On the TKX what does is use for a VSS sensor? Is it just a two wire hall effect?

I had all kinds of problems with my Intelliteonix speedo in my 84 right after my 4L80e swap. I was splitting the VSS signal to the ECU and to the speedo. Sometimes it would just drop the signal. This is common when splitting a two wire hall effect signal. So I installed front steering knuckles from an 87. That gave me a spot to install a wheel speed sensor. I just used an off the shelf high speed inductive proximity switch to see the tone ring on the wheel bearing. It works pretty well now. No more dropped signal. And the speedometer works great.

 

Odometer motor?

 

Standard 2 wire yeah. Mine just intercepts the signal to the gauge cluster before that is passed on to the ECU. That's a cool solution you came up with tho.

 

That's what I'm thinking. Previous owner had this cluster rebuilt by Batee in the last few years but either the motor isn't plugged all the way in or it's hung up from sitting because it didn't have speed input this whole time.

 

Tried taking the motor apart and seeing if I could free it up per another post from a few years ago. It was stuck solid but after some twisting with a small screwdriver/my fingers I was able to get it to turn, but when applying voltage it only ever snaps back to the same position, regardless of which way it's turning. It seems like the problem is deeper into the motor, and that seems awful, so I ordered a replacement.

 

So it turns out it's a stepper motor and this is normal behavior and the motor works fine now!