OK, I'm still having problems with my tach. It seems to work ok from idle to about 3400 RPM. After that as I give it more throttle it starts fluctuating and goes down till at WOT its at zero!
Medalion tach with MSD 6M2 box and MSD distrbutor.
Thinking its an electrical problem I've run seperate wires from the battery to the tach for power and ground. Seperate trigger wire from the box to the tach. This should eliminate the original wires in the OEM harness. I also grounded the tach to the engine with a wire but still no luck.
I have noticed that around 3200 RPM If I hit the trim button, turn on the blower or the depth sounder it makes the needle bounce?
I've called MSD and Medallion with no luck. It's hard to dial in my motor and prop with this going on!
I'm stumped, anybody have any ideas?
Thanks, Dave

I am experiencing the same problem. I have tried two new Gaffrig tachs, Ran the Tach on a seperate battery for power, and ran a new wire directly from the negative side of the coil to the tach.I was going to disconnect the alternator, change the ignition module and try a different coil but I got tired of messing with it. I was thinking that I was getting some noise introduced in the ignition system. Funny thing is that I have a digital tach on my GPS and it works perfectly

Do have a different tach to try? It's also possible the MSD is faulty. I replace those units all the time, even practically new ones.

I just had the same problem with my Livorsi tachs.I sent them back and had them recalibrated but when I got them back I had the same issue.I called and they said there is a new style tach that has all new electronics,they sent them to me and all was fixed.Not sure what the problem was but I tried all new wires and all like you guys have and nothing but a new tach helped.

Nordic95

I had the same problem with my Livorsi tachs w/ integrated hourmeter. They sent a circuit board fix, but that didn't work. They then sent a new set of tachs w/o the hourmeter and that solved the problem.

If you search the threads you will find this seems to be a common problem with tachs. I haven't found any info that defines what is going on. I'm just glad I had Livorsi's excellent customer service to back me up.

Have you tried changing the coil?

ghittner,
No I did not replace the coil. How does it affect the tachometer?

trippin,
I have not tried a different tach yet.

Does your tach get it's signal from the coil? Most systems do however I'm not sure of the MSD you have. I've seen coils in more than one instance start to make the tach jump and I've seen tachs short out coils causing a stumble, miss or the engine to cut out. I've seen it both ways. If you have an extra coil, even a stock one to test it, you might rule it out.

G,
The tach gets its signal from the box.

Had the same problem W/ MSD 6m2 boxes. I swaped tac signal wire @ guages w/ other motor and it worked fine so I replaced the box. About 50 hrs. later I have a similar issue. I would check the tac 1st. but I bet its your box. IMO MSDs work great when they work but dont seem to be very reliable.