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

Digital Tach Problem

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Old Aug 12, 2007 | 03:34 PM
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Default Digital Tach Problem

Hi ,
Im new to this forum and just purchased my first Vette a 1989 Coupe,2 weeks ago. I LOVE IT but have a small problem. I took a little trip yesterday and after about a hour of running,the Tach started to jump all over the place. I pulled over and let it idle for a minite and the Tach was jumping from 700rpms to 2300rpms just sitting there. After I shut the engine off and restarted the problem stopped.I read in a corvette parts book that there is a (Tach filter) behind the cluster that may be causing this, or is there a sending unit that feeds to the tach? I just hope you don't tell me the Digital tach is bad. Any help or thoughts would be appreciated. Thanks Wayne..
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Old Aug 12, 2007 | 06:45 PM
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95% of the time, it's the tach filter.

It converts the incoming signal from the distributor into a signal the tach can deal with.
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Old Aug 13, 2007 | 07:36 PM
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Yep, tach filter is my guess also. Look at the distrubitor connectors. Follow the "white" wire. It goes to the tach filter. Make sure the tach filter is grounded good before replacing.
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