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Thread: Holley Digital Dash Tach Issues

  1. #1

    Default Holley Digital Dash Tach Issues

    I currently have a 553-109 installed as a Stand-Alone. Using the MSD Power Grid tach output, I'm having some erratic issues. Right now the tach will jump around. Even go as high as 600K, yes 600K RPM. It seems to get worse when the headlights, turn signals or horn is activated. I've used multiple grounding sources. Power sources even going as far as running independent wires directly to battery. Still same issue. After many hours on phone with Holley, a 10K resistor was recommended. Resistor inline with tach won't work at all. Right now I'm at a loss. I don't directly think this is a Holley issue, but was hoping someone here has seen something similar and corrected. I've tried all I know to try. BTW, Digital Dash was sent back to Holley. Newest firmware installed. Tested for two days. Put it back in car same issue. MSD Power Grid gauge doesn't show the erratic spikes, just on the dash.

  2. #2
    Join Date
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    Default

    Quote Originally Posted by 1fast10 View Post
    After many hours on phone with Holley, a 10K resistor was recommended. Resistor inline with tach won't work at all. Right now I'm at a loss. I don't directly think this is a Holley issue, but was hoping someone here has seen something similar and corrected.
    This reminds me of this post: https://forums.holley.com/showthread...4969#post84969
    May God's grace bless you in the Lord Jesus Christ.

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  3. #3

    Default

    Danny, I read that post and my issues are very similar. However, a 10K resistor doesn't even allow tach signal to work. Smaller resistor values the tach will work, but problem exists still. I'm almost certain it's a car issue, just don't know what. For instance, I can unhook all headlight, parking, turn & horn wires; yet when I activate them, the tach will still act up. The horn is the worse. I can't completely disconnect steering column, and obviously the horn isn't a issue anymore, but the headlight switch still is.

  4. #4

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    1fast10, did you ever find out what the issue was, because I'm having the same problem with the tach reading? I've also tried the resistor, and it did not work.

  5. #5

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    I'm currently having the same problem. '04 Corvette ECU, +12V square wave white wire from ECU, tach jumps around at idle, off idle works fine. Sometimes it glitches when high-beam/HB indicator is on. Anybody find a solution to this problem? Also tried resistor with no success. Thanks!

  6. #6

    Default

    Bringing this back from the dead. We have found no fix for this car. It does go away if we unhook the 1-wire alternator. Install a brand new alternator, same issues. No alternator, no problems. We even have a MSD noise filter on the main power feeding the Digital Dash & MSD Power Grid.

  7. #7

    Default Fix

    I was told by Holley they have a fix for it. It's some type of harness, when I called them about this problem.

  8. #8

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    Quote Originally Posted by Stang986 View Post
    I was told by Holley they have a fix for it. It's some type of harness, when I called them about this problem.
    Do tell, please. What is the PN for the harness?

  9. #9

    Default

    Same issue. Tach works normal driving, but under load, the tach jumps all over the place. MSD box shows smooth on logger. Bump for solution.

    UPDATE: I added a the Holley LED Light Bar to my Digital Dash recently. At the track it's horrible. The light is constantly flickering going down the track. The datalogs taken with the stand-alone just show a bouncing tach signal. Resistor values above 2K Ohms show a low or no tach signal. I currently have a 1K resistor in the tach line, but it will still pop the shift light on driving. Unhooked nearly all wires trying to solve this issue, with zero luck. Bump for any useful info, or new ideas.

  10. #10

    Default

    I was having an issue with erratic to no tachometer on my stand-alone Digital Dash. Nothing fancy or elaborate with the ignition system; basically a MSD 6AL. I'm using the output terminal straight out of the box and connected to B5 at the dash plug.
    Holley engineers came to the rescue with a buffer/filter, part number C460434. Installed the part and all works great!

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