Biggus

iTrader: (1)

I had a similar issue last season. My stdb tach would flutter and the engine was skipping at higher rpm's. After a bit of troubleshooting, we found the problem to be a loose ignition module ground.

GAUGETHIS

The tach suppresor goes in line on the signal wire. It is a simple install. Also bad spark plug wires could add to the signal noise on tach and will give it iratic readings.

blue thunder

Can you give me a part number and contact for purchase?

eichhoma

iTrader: (1)

This is everything we tried:

used an MSD tach generator, simulating engine running, tested good, tachs worked fine to the rev limiter.

Other grounds at gauges were checked; all were good, showed 12.9 volts at each gauge positive to negative.

Also did a sweep test on each gauge by grounding sensors on both motors to a known good ground, function tested normal.
Sytem voltage is 14.2 volts on both engines idling.

Hooked a known good ground wire to every ground possible on both engines, did a test run after each connection.....

Tachs work great right up to about 3800 RPM, and they both STILL start fluttering and go back down toward zero.
I am really at a loss here....
Anything I am missing here, this is really baffling me here, more suggestions would be much appreciated....

Thanks. Mark

bob_t

This may seem like an odd way to check your tachs, but see if one of your friends wouldn't mind putting YOUR tach in his boat. If it works (which, from your MSD generator, would suggest that it will work just fine), you have ruled out the tach. One of my boats had a similar problem where the tach and water temperature gauge (but none of the other gauges) were fluttering/spiking and we checked everything ... except a couple months later the alternator literally fell apart ... the long screws that held the cases together had vibrated out. Made a mess of the alternator, but, when it was rebuilt, the gauges quit their eratic traits.

Griff

Did you use new spark plug wires with new engines or reuse the old ones????

What are the ignition modules bolted to????

Boat Tech

X 2, start the engine up then go back and wiggle the main power wire harness and watch all the gauges and see if they wig out at all or some times the engine will die.

BenPerfected

If the new engines have fresh paint, we always removed a spot to paint where the V-6 module are bolted to the blocks. Did you change anything in your main grounding set up from the batteries? How about the ground jump from engine to engine?

eichhoma

iTrader: (1)

Brand new spark plug wires. It did it right off the bat with a new pair of taylor's on there. Even replaced those Friday with a new set of MSD wires that have a lower resistence rating....

Factory location, and they are grounded, paint is not an issue.
No loose wires, or grounds, we checjed every one and polished each one up.....

eichhoma

iTrader: (1)

We did this too.... well not the wiggling it while it was running but we cleaned each prong and spread them out a little so they would make a better connection....

What is strange here, is this seems like the tachs are getting some kind of "interference" at the same time, at the same rpm.... what could cause that?/ We are starting to think about the alternators, maybe disconnecting the purple wire from the alternators, and see if it is cooming from them....

We have had the Mercury manual out for the last two days following the entire wiring diagrams.... We are running out of things to look at.... but SOMETHING is causing this!

I will try wiggling the cannon plug while motors are runnning and have someone watch the gauges this morning.

Please keep throwing ideas our way please! I appreciate it!