Dakota Digital Speedo Box Issue.

[Ccmano]

Has anyone else run into this... changed the diff to a 4.10 and needed speedo correction. Picked up a Dakota Digital SGI-5c, I've done this before with no issues. Wired it in to the yellow VSS wire as directed, provided power and ground to the DD box.

It works fine, however, intermittently, when the car comes to a stop the speedo will read fluctuating speeds from 1 to 100 mph. The car is not moving but the speedo reads the fluctuating speeds! I contacted Dakota Digital and was told I'm getting ground interference.

I've moved the ground three times the last being to the transmission itself and still have the problem. I checked and retightened the battery negative cable at both the battery and where it grounds to the block. I retightened the positive cable as well. The battery checks out with a resting voltage of 12.9 volts. I have routed the signal wires away from each other and made sure they are not next to any other wiring.

I'm running out of ideas. I suppose the alternator could be a cause however there have been no other electrical issues with the car.
Any help would be appreciated. This post will be found in other forums as well.
TIA
H

[geezer]

Long ago ,if I remember correctly I had this issue with a long gone vehicle & noticed that if the load on the elec. sys was changed ( brake pedal) it would drop to zero. So perhaps it was related to power side. Ran a line direct to battery & problem solved. Box current draw is minimal so wasn't concerned about powering all the time. If that should be of concern use a relay for power when key is on.
Worth trying ?? :)

[Ccmano]

Long ago ,if I remember correctly I had this issue with a long gone vehicle & noticed that if the load on the elec. sys was changed ( brake pedal) it would drop to zero. So perhaps it was related to power side. Ran a line direct to battery & problem solved. Box current draw is minimal so wasn't concerned about powering all the time. If that should be of concern use a relay for power when key is on.
Worth trying ?? :)

Thanks, going direct to the battery for power was going to be my next test. I suspect however the alternator/voltage regulator may be the issue. I want to eliminate all other possibilities before I pull the alternator for testing.
H
:cheers:

[Mikey]

Try tying ground to the same point as VSS and ECU.

[Ccmano]

Try tying ground to the same point as VSS and ECU.

It's currently grounded to the transmission body. The ECU grounds to G105 and G106 where the bellhousing bolt mounts to the engine at the upper driver side mounting bolt. Attaching the ground to the transmission should accomplish the same thing.

The VSS doesn't have an actual wire ground. It's actually a signal (voltage) generator not a true sensor. As such the two wires coming from it provide reference signals to the ECU. The yellow wire is the high speed signal and the purple wire is the low speed signal. I believe grounding is accomplished via the mounting to the transmission case.

If my theory is correct this should technically accomplish grounding to the same grounds as the ECU and the VSS.

Obviously that's not working out.

My next step will be to wire directly to the battery positive and negative.
H
:cheers:

[Mikey]

Attach to the exact same bolt the ECU ground is at

[Ccmano]

So... I tried grounding to G105, G106 and direct to the battery. No change. Still randomly shows speed on the speedometer when standing still. As previously noted G105 and G106 is where the ECU grounds. They are two grounding bolts adjacent to the top bolts (right and left) that hold the bellhousing to the engine. The next step will be to change the positive connection. I'm open to suggestions...
H
:cheers:

[Corvette95]

So just thinking, what about wiring your sensor with two "Y" connectors in parallel to a DVM and see a watch the linear curve up and down and then to idle. Kinda of like taping a fuel gauge to your windshield. See if you are getting feedback or find current where it should be zero. Trace back erroneous voltage to its source via a powered circuit tester? I am just spit-balling. If that works you will have several option to correct it.

[WARP TEN]

Hope you get it figured out Hans. But I was wondering, why didn't you just replace the speedo gears rather than go electronic? I had 4.10s put in both my '93 and '95 and I tried an electronic speedo correction unit for a while on the '93 but it never really worked right (older '90s technology was probably the culprit) so I had Marc put the speedo gears in. Never had a problem after that and did the same on the '95 when I got it. --Bob

[Ccmano]

So... the answer is AC voltage ripple! No it's not a new adult beverage. This was a learning experience for me. I was probably taught this some where along the line but have since forgotten. Replacing the alternator fixes it. It has seriously bad implications for the cars electronic components. It took out my battery too. Otherwise I think I caught this in time.

I'll be putting up a new post in the next few days to explain in more detail. I may even turn this into a HOTB article.
H
:cheers: