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Topic: Not your everyday tachometer tach problem

Not your everyday tachometer tach problem (1/2)
 6/6/18 12:36am
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Stanwood, WA - USA

1978 black on black 350

Joined: 6/15/2017
Posts: 3

Hi All - Iíve read through (what seems like) 100s of ďtach problemĒ threads, and I havenít found anyone with this particular problem yet. My tach has been working flawlessly since I got the car a year ago. Two days ago it decided to basically start showing power on at 1500, idle at 2000 and stops advancing at about 3800. It does advance smoothly with the increase of engine speed - doesnít jump around or just sit in one place or peg itself at 7000 (like all those other threads Iíve read). It did do this once before for just an hour or so, then went back to normal. No such luck this time. Most threads suggest checking the filter that sits between the distributor and the tachometer...tested (no issues there). I also checked the separate wires by disconnecting the red wire from the distributor (car died as expected - tach still read 2000), disconnected the black wire (tach stopped registering change in engine speed as expected - still at 2000). I have not pulled the tach to see if there are any shorts on the circuit board, but that seems unlikely since it does advance with engine speed and drop a bit with power on. Anyone have a similar situation and possible solution?
P.S. Probably unrelated but Iíd better mention...I replaced the stereo using the existing wiring just prior to this starting.
On a similar but different note...I was thinking of replacing all of my gauge clusters with digital displays. The ones Iíve seen so far claim to drive off of the existing connections, so Iím thinking this readout problem wouldnít go away. Thoughts?

|UPDATED|6/5/2018 9:36:31 PM (AZT)|/UPDATED|
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Re: Not your everyday tachometer tach problem (2/2)
 6/7/18 3:03pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19720

 It's possible that the gauge itself is out of whack. Then again, tach problems on these have normally been traced to either the filter or the circuit board. I would suspect the circuit board, before condemning the gauge itself. Unfortunately, the only way to check is to replace the board, unless you have a certified instrument repair place close to you. Unhappy

Joel Adams
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