C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Tachometer Not Working Correctly!

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Old Jun 23, 2022 | 04:49 PM
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Default Tachometer Not Working Correctly!

Took my 89 Corvette out today for a 70 mile drive this morning to blow the cobwebs out of her. In doing so, I noticed my tack saying the engine is hitting 7k rpm. Well there’s no way that’s possible! Any suggestions on what may be the cause of it?

Video I took of the tachometer during an acceleration:
https://youtu.be/Ufv5nmaZyP8
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Old Jun 23, 2022 | 04:58 PM
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Probably the Tach Filter
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Old Jun 23, 2022 | 05:20 PM
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Where can they be bought? I’m finding the GM unit is discontinued.
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Old Jun 23, 2022 | 05:22 PM
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Probably the corvette aftermarket spots like Ecklers/Mid America, etc. Its the same filter for late 70s through 89 as I recall.
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Old Jun 23, 2022 | 08:20 PM
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easy swap cornhusker 👍
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Old Jun 28, 2022 | 01:57 PM
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Originally Posted by vader86
Probably the Tach Filter
My tach has been doing the same thing (1989 6 speed). It has told me to upshift even in 6th gear. Speedometer also works intermittently (sometimes believable, sometimes inaccurate, sometimes says 0 even though at highway speeds), which also is killing my mpg calculation. Oil temp was reading Lo for a while but it seems to be working again. The horn has also stopped working.

But more concerning is the issues started with the fuse for turn signals and back up lights keeps blowing as soon as turning the key to accessory, and it will now occasionally just shut off but start right back up with no issues. Could a bad gage cluster or tach filter be the source of these symptoms?
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Old Jun 28, 2022 | 03:39 PM
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Originally Posted by MatthewJP
My tach has been doing the same thing (1989 6 speed). It has told me to upshift even in 6th gear. Speedometer also works intermittently (sometimes believable, sometimes inaccurate, sometimes says 0 even though at highway speeds), which also is killing my mpg calculation. Oil temp was reading Lo for a while but it seems to be working again. The horn has also stopped working.

But more concerning is the issues started with the fuse for turn signals and back up lights keeps blowing as soon as turning the key to accessory, and it will now occasionally just shut off but start right back up with no issues. Could a bad gage cluster or tach filter be the source of these symptoms?
That seems like a short, but not specifically in the VSS or Tach filter, though those may be bad.
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Old Jun 28, 2022 | 08:34 PM
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Worked for me!

https://www.ebay.com/itm/15467065116...UAAOSwXmlhg-tJ
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Old Aug 22, 2022 | 04:14 PM
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I was just going over the engine & cannot find a Tach Filter, anyone know where it’s located? My FSM isn’t helping me at all.
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