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Thread: Speedo Calibration Issues

  1. #1
    Senior Member kraftee's Avatar
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    Speedo Calibration Issues

    Has anyone else run into a situation where the speedometer only "sees" pulses above about 40 mph? Makes it a b1tch to calibrate. Bad speedo head? Bad VSS? I'll contact Autometer on Monday I guess - unless anyone has a quick fix. ERIC
    "If everything seems to be coming your way, you're probably in the wrong lane."

  2. #2
    Senior Member kraftee's Avatar
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    STILL not fixed!!!

    Contacted Autometer. They suggested it might be a bad VSS. So I replaced it. Still does the same exact thing. Here is how I have the speedo wired: First, the Ron Francis EFI harness has a two-wire connector with orange and green wires that plugs directly into the VSS. The green wire is labeled "ECM 3 VSS POS". The orange wire is labeled "ECM 3 VSS NEG".

    Next, the speedometer itself has four leads connected to it. First, the brown wire that runs 12v switched power to all the gauges is connected to the "12v" prong. The white wire that runs power to all gauge lighting when the headlight switch is pulled is connected to the "LAMP" prong. The black ground wire is connected to the "GND" prong. Finally, the green wire that is spliced into the VSS green "ECM 3 VSS POS" is connected to the "SIG" prong on the speedo. There are four other empty prongs on the back of the speedometer. The attached pic shows the layout. Anyone have a suggestion?
    Attached Images Attached Images
    "If everything seems to be coming your way, you're probably in the wrong lane."

  3. #3
    Senior Member kraftee's Avatar
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    Well, after much gnashing of teeth - and wasting of money - I finally have a functional speedometer. Here's how it happened:

    As I said above, replacing the VSS unit ($40) did no good at all. So, I reasoned, it MUST be the speedo itself. The first time I connected it, I had some wires wrong - so, again I reasoned, I must have damaged the electronic speedometer. Ordered a brand new one from Jeg's ($150) and installed it. Still exactly the same issue. The speedometer doesn't see any pulses at all until about 40 mph. And above that it's pretty erratic. Crap. Checked continuity and grounds (again) - all appear good.

    So, after wasting right at $200, I swapped the original speedometer back into the dash and the new, zero mileage one back into its box (anyone wanna buy a new speedo - cheap?) Then (in another attempt to throw large sums of money at an unsolvable problem), I said to hell with it and ordered Autometer's GPS interface kit ($200). Installed the kit this morning and attached the antenna puck underneath the cowl. I have a Livorsi GPS speedo in my Donzi and the speedo puck picks up just fine through the fiberglass deck. So, I figured it would work fine through the 'glass cowl. Nope. Gotta have a clear, unobstructed view of the sky.

    After casting about for SOMEWHERE unobtrusive to mount the magnetic antenna puck that still gives it a clear view of the sky, I decided (how's this for some real out-of-the-box thinking?) to install it on one of the front right suspension links - just outside the bodywork. Ran the wire, connected everything, looks pretty unobtrusive, and wonder of wonders, it works perfectly! Even though I still have no idea why it would not work with the VSS, I don't care. Celebrating right now with a cold beer...
    Last edited by kraftee; 08-24-2017 at 05:07 PM.
    "If everything seems to be coming your way, you're probably in the wrong lane."

  4. #4
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    I had a very erratic speedo where the needle would bounce wildly and was told by FFR and the speedo tech guys that the speedo cannot share ground with other instruments, so I made a new ground path and it fixed the speedo.

  5. #5
    Senior Member kraftee's Avatar
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    Wish I would have know that before spending $400 to get the thing working. That was probably the original issue...
    "If everything seems to be coming your way, you're probably in the wrong lane."

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