So I posted a thread earlier about my speedo not working, however I'm pretty sure I've sourced it to the Modifry yellow jacket not functioning properly.

When I power cycle the YJ it will work at first, and this is shown by the unit blinking about once a second while the car is moving, however when the speedometer cuts out, the YJ's LED stays lit forever, I looked up Modifry's site and while it does have some diagnostic attributes, I did not see anything about the LED staying lit 100% of the time while malfunctioning.

Does anyone have an idea what the source of the problem would be? Is my unit just bad and I should just replace it with another one? Granted it's about 3 years old, and had worked flawlessly before that.

I'll probably email Modifry as well to get their take on the matter, but sometimes the turn around from them isn't the best, so figured I would post up first!

 

Mine did the same thing and the ground was the issue. After about 3 years of flawless operation it started gliching and I would get a 0 MPH reading on my speedo and the EPS light would trigger.
You need to re-ground the unit to the engine block or frame of the car, the ground needs to be rock solid! Good luck

 

Interesting, I have regrounded it once already as well as replaced the ring terminal that it currently had, maybe the ground wire is loose in the harness or something because I would imagine that where I have it grounded is fine (hood release bracket)

Anyways I'll ground it to something else and check the harness and maybe tape it up a bit.

Thanks for the input Puddy!

 

Has Modifry responded? Was this a new purchase or something you've had for a while?

Anyway, I have a yellojacket sitting in my parts bin which is practically new. It's yours if you want it.

 

He hasn't responded yet, I've had it for 3 years like Puddydad had his when it started acting up. I haven't had a chance to try a new ground yet, but if that doesn't work I'll be interested!

 

I started with the Yellow Box about 11 years ago. After a couple of years, it went erratic so I got the Yellow Jacket. It worked fine for many years until about 2 years ago when it would settle in at "0" when I stopped at a red light and stayed there after I started moving. I relocated the ground to the engine and it seemed to work again but a few months later, it started to do the same thing. Modifry and I communicated back and forth a few times and he offered to send me a new one but I said to hold off since the problem was so intermittent. After over a year and having done nothing, everything continues to work fine, so I haven't had to deal with it again.
I found that when the speedo stuck at ZERO after I started moving, the CEL for VSS came on after a few miles. However, if I keyed the ignition OFF and back ON quickly while moving (and before I had driven too many miles), the speedo started to work again and continued to do so for several days to several weeks. To this day, I have not found out what exactly was going on. I can only surmise that since we have a 12V system, but the VSS is only about 5 volts, grounding is very essential to ensure the small voltage gets through in a linear fashion. It's the varying voltage from zero to 5 that the ECU interprets as varying speed.

BTW, Modifry (Bob) is semi-retired and does the S2000 electronic thing as a hobby side line. He may still be on vacation from the holiday season.

 

Well Bob messaged me back earlier today and told me that he's heard of it happening a couple times and mentioned that it was always related to a bad battery, so maybe xviper you just happened to change your battery which cured your problems.

Unfortunately for me however, I literally had a bad battery that got replaced under warranty about 2 weeks ago, everything was fine until I tried to install that serial gauge, and now I'm starting to think it truly was just a coincidence that the yellow jacket started acting up the day after I installed it, because I have literally reinstalled that whole damn thing multiple times, with and without all my other electronics and I can't get it to work.

My battery is less than two weeks old and everything else works perfectly, I moved the ground per Puddydad's advice earlier today and I *thought* it had solved my problems as I drove around for about 10 minutes and didn't have any problems, but after I turned the car off, and then drove around again about an hour later I didn't even make it a mile before the speedo went to zero. Right after it went out, it would occasionally come back and read correctly, and then it seems like the voltage just dropped because the speedo would actually read a lower mph (was going 35, then it read 23, 17, 8 then Zero and it stuck.) It's currently grounded to one of the locations that the stock ecu bolts onto.

99SH hooked me up with his yellow jacket he had laying around, so hopefully that will get mailed out tomorrow and I'll have it in a few days and can swap the units out to see if it truly is the unit that's bad or if I'm just a terrible electrician

 

As XViper explained so well and I stated, the ground has to be rock solid. You need to ground it to the engine block or frame. Clean any paint off the area you use to ground your wire too.

Good luck