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Old 05-11-2024, 06:11 AM
CROS34 CROS34 is offline
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Default Tach to max RPM

Every time I turn the car off the tach pins itself to max. After starting, it stays there until the throttle is tapped to maybe 2K. Than it snaps back into the game and works fine.

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Old 05-11-2024, 07:03 PM
70GS455 70GS455 is offline
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Aftermarket tach?

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Old 05-12-2024, 06:27 AM
CROS34 CROS34 is offline
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No factory

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Old 05-13-2024, 10:10 PM
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bhill86 bhill86 is offline
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Not uncommon in the later version of the 2nd gen tachs. Late 78 thru 81 are the same. Something causing a surge after the ignition is turned off sending the tach to full tilt.

New circuit boards are available for about $55 and not difficult to change however after speaking to the maker of the boards he wasn’t positive if that would solve the issue or not. May be worth a try though.

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1977 Trans Am 400/4speed (swap)

Brian
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Old 05-13-2024, 10:12 PM
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Here’s the link to the site https://www.cajuntachshop.com/

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1977 Trans Am 400/4speed (swap)

Brian
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Old 05-14-2024, 12:47 PM
CROS34 CROS34 is offline
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Thank you I will look into.

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Old 05-15-2024, 11:15 AM
MO Olds MO Olds is offline
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I would check your ground on the tach. I added an extra ground to one of the screws/bolts on the back. I also bought a board from Cajun tach shop and probably the nicest person to work with, the board itself is very high quality in my opinion. I also like the adjustment built into the board; it's not advertised on the site but in the instructions, you can dial in your RPMs if you have a digital timing light for example to compare it to.

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Old 05-15-2024, 11:26 AM
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bhill86 bhill86 is offline
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MO olds, were you having the same issue as him with the needle pegging? And if so did some combination of the new board and a ground fix it?

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1977 Trans Am 400/4speed (swap)

Brian
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Old 05-15-2024, 11:55 AM
MO Olds MO Olds is offline
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Quote:
Originally Posted by MO Olds View Post
I would check your ground on the tach. I added an extra ground to one of the screws/bolts on the back. I also bought a board from Cajun tach shop and probably the nicest person to work with, the board itself is very high quality in my opinion. I also like the adjustment built into the board; it's not advertised on the site but in the instructions, you can dial in your RPMs if you have a digital timing light for example to compare it to.
Quote:
Originally Posted by bhill86 View Post
MO olds, were you having the same issue as him with the needle pegging? And if so did some combination of the new board and a ground fix it?
Yes, almost like on new cars where all the gauges spike them go back down. The new ground helped until the original board went bad. I also cleaned up a lot of the contacts and wires. Eventually one of the capacitors swelled.

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Old 05-15-2024, 01:36 PM
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Interesting. Good to know, thanks. CROS34, if you try a new board will you report back please?

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1977 Trans Am 400/4speed (swap)

Brian
  #11  
Old 05-17-2024, 07:04 AM
CROS34 CROS34 is offline
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I will remove cluster first to review ground, and correct if an issue. If that's not it, I will clean all contacts and connections. I want to take it a step at a time, so I know what fixes the issue. Thanks way the next guy doesn't have to. Thanks. I'll report back when I know more.

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