Strange tachometer issue

CaptMike · Post by **CaptMike** » Tue Jul 31, 2012 11:30 am

Ok. So this is an issue that has stumped a couple of mechanics so far. My starboard 454 has a tach flutter only when the port 454 is reved up in neutral to about 1600 rpms or higher and when in gear at about 1200 or higher at all higher levels. The starboard tach will dive down about 100-300 randomly. There is NO movement in the starboard tach when we run it alone (no port engine power) or when the port engine is at minimum throttle in gear or in neutral. When you bring the port engine up in RPMs, the starboard tach starts to bounce.

We cannot feel any hesitation in the engine as in it slowing down or jerking back. Sometimes we think we can hear something, but we can't tell for sure. The starboard 454 just received a fresh tune up (wires, plugs, rotor and cap) we also checked the timing to confirm and that was "very very close to perfect".

The jumping tach also effects the synchronizer gauge too. When the starboard tach jumps the sync gauge jumps too. The port tach is always steady. The mechanic hooked up a manual tach to the starboard and that was steady according to them, but I know those are not as sensitive. The gauges are VDOs

Current running theories are some sort of electrical corrosion on the contacts of the starboard gauge that is creating the jump when the rest of the boat is drawing pwoer from various systems that are running randomly etc. The other question was if my boat had a power combiner. I don't know. They thought it may be something do with the starboard engine not drawing enough power.

The next project is too open the helm, check the contacts, and clean them if necessary.

ANY ideas?

koviak · Post by **koviak** » Tue Jul 31, 2012 1:28 pm

On the back of the tach is a small selector switch rotate this around a few times and recheck. Corrosion builds here and give a poor connection.

alexander38 · Post by **alexander38** » Tue Jul 31, 2012 6:06 pm

+1 one the switch, and it seems the older they get the more it needs to be done.

jefflaw35 · Post by **jefflaw35** » Tue Jul 31, 2012 9:53 pm

alexander38 wrote: more offend they need turned.

LOL really? That is some really funny stuff!!!!

...... Love you Guys!!!!

Did you mean to offend him or did you mean he should do this routine often?

Commissionpoint · Post by **Commissionpoint** » Tue Jul 31, 2012 11:42 pm

The more I get offended the more I need 'tuning' too. (The antithesis of that is the more I offend folks the more tuning they end up needing.)

I agree 100% though. The selector switch gets effed with time and corrosion and, as aptly stated already, more often than not, causes the tach to do funny things when its not meant to.

http://www.caig.com/

Learn it.
Live it.
Love it.

If you own old stuff with contacts of some sort this is your new best friend. Love your hobbies, not spending needless money replacing perfectly good but old components.

Besides..... What can you buy now without getting a second mortgage that compares to off the shelf stuff from 30+ yrs. ago? Keep your old stuff going. It just takes the right group of folks to help you do that. You couldn't be in a better place if that old thing you are trying to keep going is a Trojan.

alexander38 · Post by **alexander38** » Wed Aug 01, 2012 6:04 am

jefflaw35 wrote:
alexander38 wrote: more offend they need turned.
LOL really? That is some really funny stuff!!!! ...... Love you Guys!!!! Did you mean to offend him or did you mean he should do this routine often?

My bad...

Allen Sr · Post by **Allen Sr** » Wed Aug 01, 2012 6:40 am

alexander38 wrote:
jefflaw35 wrote:
alexander38 wrote: more offend they need turned.
LOL really? That is some really funny stuff!!!! ...... Love you Guys!!!! Did you mean to offend him or did you mean he should do this routine often?
My bad...

Hey Jeff, REALLY?............Give Tony a break.......he was having a SENIOR moment!

TBone · Post by **TBone** » Wed Aug 01, 2012 8:22 am

I would start by cleaning or replacing the terminals at the tach and the dist. And then start her up and see what happens. If it is still doing the same, try making a jumper. Jump directly from the dist. tach. lead to the actual tach no need to make it pretty, its for testing purposes. If the problem is fixed with the jumper, could be a bad wire. If its not, i would look at the engine sync. Disconnect that, see what happens.

Tom

TBone · Post by **TBone** » Wed Aug 01, 2012 8:24 am

Oh yeah, almost forgot, make sure all your grounds are clean

Tom

CaptMike · Post by **CaptMike** » Wed Aug 01, 2012 8:39 am

Great. Thanks for the advice. I will look at the wiring and twist the nobs. Is there any way it actually be losing power. Can the port engine reduce the power of the starboard?

Big D · Post by **Big D** » Wed Aug 01, 2012 8:26 pm

You may have more than one issue here. Certainly rotate the cylinder selector switch several times back and forth as mentioned, this is usual the cause of such symtoms, and check wring and connections as mentioned. The hardware common to both engines is the sync and may be the reason why you're getting a reading on the non-running engine's tach too. Take the sync out of the equation to see if that will isolate tach operation re working while opposite engine is running.

prowlersfish · Post by **prowlersfish** » Wed Aug 01, 2012 8:42 pm

I have seen the synchronizers cause all types of problems from tachs to no starts to poor running

jefflaw35 · Post by **jefflaw35** » Wed Aug 01, 2012 10:03 pm

Allen Sr wrote:
alexander38 wrote:
jefflaw35 wrote: LOL really? That is some really funny stuff!!!! ...... Love you Guys!!!! Did you mean to offend him or did you mean he should do this routine often?
My bad...
Hey Jeff, REALLY?............Give Tony a break.......he was having a SENIOR moment!

Oh my bad!!

jefflaw35 · Post by **jefflaw35** » Wed Aug 01, 2012 10:06 pm

Commissionpoint wrote:The antithesis)

Would you stop it with your big a$$ Google me! Words, sheeeesh LMAO!!!