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Tachometer doesn't work when car is moving

by Pertti Harkonen
(Caravaca de la Cruz, Spain)

When I got my 1978 Corvette, the tachometer was just moving wildly around. I bought a new Willcox tachometer card and after installing it the meter worked correctly in every possible rpm. I thought that the problem was solved, but when I started to drive the car out of garage the meter went haywire, showing between 0 and 4000 rpm in very rabid fashion. I thought that the problem must be the filter. Well, there was no filter at all, somebody had connected tach wire directly to HEI. I bought a new filter and installed it according to instructions brown wire to HEI and white wire to tach in it's original place top of the intake manifold. I cleaned the base very well so ground connection is good. No help at all. Things didn't change. When the car is moving slowly the meter is just crazy and when the speed goes up more than about 30 mph the needle freezes at six o'clock and stays there. At the complete stop it shows correct rpm again. What to look next?

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