I have a 502 mag with a Vortech supercharger on it. When I purchased the boat the owner installed a Gaffrig digital GPS speedo. The speedo also has Tach, voltage, and compass functions. The analog tach that came with the boat would operate till 4krpms then drop to 0 if the rpms went any further. The digital Tach would read properly all the way to the revlimiter @5400. Bought a new Gafrig tach and this one would not go above 4k reguardless of rpms. Called Gaffrig and they sent me a new tach that they tested prior to shipping. Put this tach in and it reads to about 4500 then drops to about 3800. All the while the digital tach operates properly. I have disconnected the digital tach and the analog tachs still operates the same. Any Ideas
Ran a seperate wire directly from the coil to the tach and used a seperate battery by itself to power the tach and it still acts the same. Does anyone know if the ECM could be wacking out the tach signal?
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