I have an issue with two brand new Livorsi tachs installed on twin HP500 (EFI). The tachs both run perfectly until I hit 3200 rpm. Once I get there they start to bounce all over the place from 2500-4500 rpm. I just removed two older tachs that still work fine - any ideas? I'm running non-resistor plugs but not sure that would have any bearing. Anyone had a similiar issue? I'd really appreciate any help.

Check the wires going to the dist. vibration at 3200 could be bouncing the wires or ground

Mine was doing that and I re-routed the ground wire from the dist. and mine is rock steady now...Check your ground!

My coils have a sealed plug on them. I don't see any way that I could rewire them or check to make sure the wires are tight. They just plug right into the coil. The other thing is the old tach works fine so why would new ones be different?

Had the same issue with a former boat, 502 mpi - ended up getting a filter from Livorsi.

I had the same problem and fought it for a few weeks... chased down grounds, sender wires, dist., coil, added an inlinie filter...even went as far as changing alternators to see if the interference was coming from them... finally talked to livorsi and they changed my new tachs out to the ones that have the built in filters and the problem disappeared...