Finally!! NA speedometer and cruise control
 

After a year of driving my car without a working speedometer or cruise control and using a GPS iPhone app, I finally have a working speedometer.

My buddy wanted some wiring work done to his truck and ordered the Dakota Digital ECD-100 from Summit for me in exchange for the work.

I've heard good and bad things, mostly bad, about these things but I figured it was the only way to keep my NA cluster and have a factory cruise control setup. Since they don't make a unit for a Miata, I had to reuse the original cable end and connector. I found that gently heating the nylon connector with a heat gun softens the bond just enough to allow it to be removed with a gentle tug. Same goes for the cable end. Removing the GM end of the Dakota cable was just as easy, I simply cut it off. After a couple trial fits, I got the cable and sheath lengths just right to allow everything to line up and work smoothly. The wiring was even easier with only four wires: +12v, ground, signal and a calibration wire. It came with a momentary pushbutton switch which gets wired between ground and the calibration wire.

Once I had it wired, I turned on the ignition and entered the calibration mode. The speedo jumps to and stays at 30 MPH to let you know you're in calibration mode. It was a bit odd seeing the speedo at 30 and hearing the cable spin while sitting still in my garage and wondering if I would be able to hear it while driving. I drove out to a deserted road and started the calibration process which is a matter of driving at a constant speed while pressing the switch to increase or decrease the indicated speed. with the engine running, it's much louder than the spinning cable and there's no way I'd ever notice the sound. I honestly can't believe how smoothly the unit operates. There's no shudder in the needle at all, it just works as intended all the way down to zero. It even indicates my speed in reverse!

My only issue now is the cruise control. I tested it on my way to work this morning and found that it oscillates quite a bit. I'm using the factory cruise control setup and I think it may be somewhat to blame. It worked great with my original 1.6 but not so great now. I believe it was only calibrated for the power and acceleration of the original engine. For instance, if I set it at 50, it used to hold that position until the speed dropped to 49 and then apply the throttle until the speed again reached 50. with the LS1, things are a bit different. even in 6th gear, it applies the throttle at 49 and way overshoots 50, more like 53-54. It then releases and the speed rapidly drops back to 49 and the process repeats again.

Has anyone else had this issue? I'm thinking about installing a restrictor orifice inside the vacuum line going to the unit, hoping it will slow down the rate of acceleration.

Thoughts?

I'm not sure that would make any difference. The restrictor just makes it slower for the vacuum to equalize on either side of it and you'll still have the same amount of vacuum power at the cruise after a few seconds. Basically it acts as a delay. Maybe if there was some way to step down the vacuum there to 5 hg or so it would settle it down.

For what it's worth I'm running the old style vacuum Audovox unit and it's just holds the RPM at the set point. It doesn't even have a speedo input to it and it's really smooth even in hill country.