maybe this will help for whomever. We deal with Faria since they are installed in a lot of boats - from Baja back in the day to most family rec boats

http://faria-instruments.com/site_ma...achometers.pdf

double post

Yes just analog gauges.

Yes sir.... tried to no aval

I had the bouncing tach problem on my Formula 353 w/ twin HP500 EFI's. Went through all the troubleshooting stuff discussed here: swapped tachs, plug wires, checked grounds till sunrise, etc.. No joy until...

Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple to hook up a temporary jumper to confirm that it solves the problem for you.

Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding of the distributor base apparently only serves to ground out electrical noise from the ignition appearing on the tach signal wire.

Guys its a distributorLESS engine 496 / 8.1 It gets its tach signal from the crank sensor / crank reluctor . How does your engine run because the crank sensor does has all to do with the rpm signal.

Not sure if anyone will see this but anyone ever find out what the solution to this problem was for bouncing tach with merc 496? I'm having similar issue except my tach moves when key is turned on then when starting it gets pinned all the way down. So I know it's getting power, just no movement when boat is running. I'm not sure if my faria tach with hour meter just went on me or it's just a ground issue. Where does the gray wire go too from the harness plug at tach? There is no distributor on this 496. Just 8 coil packs & ECU. Any suggestions Bup?

If it is an analog Faria tach try this:

My Starboard tach was all over the place, I got in behind the dash this past weekend to turn the pole setting dial back and forth to clean the contacts. This is the dial that designates what type of engine the tach is hooked to (4,6 or 8 cylinder) which i did and also discovered that the tach was also set incorrectly. Turned it back and forth a couple times then set it correctly and my problem is fixed!

Also quick note on the Faria Tach pole setting dial;
1 = 4 CYL
2 = 6 CYL
3 = 8 CYL

Ok, I'll give that a shot, but I think it's the gauge itself. I'll get back to everyone when I figure it out.