Tachometer Issue

[tommyt]

I searched for this and did not find anything like it. So........


2004, C34, M35

About 2 months ago my tach was acting up. Registering much higher than I knew it to be, especially at idle. Then, it corrected itself. Idle was consistent, and tach registered where it always had at certain speeds and weather conditions. Breathed that sigh of relief you know you will pay for later, and everything was fine.

Until this weekend. Start the engine and at what I know is 800-1000 RPM idle it reads 3000 RPM. Hit the throttle a little and it pegs. Three days out, same thing.

OK, any simple ideas? I am having the engine tuned in a few weeks as I am just not happy with how it idles. Starts and runs fine, but even after checking alignment it just does not make me happy. I will have them look at the tach, but would rather correct it before a two weeks cruise if I can.

Any and all ideas accepted.

[Stu Jackson]

Tuning a diesel engine?  Not quite sure what that means.

As far as your tach is concerned, have YOU checked the wiring, all the way from the tach itself back throught the wiring harness to the alternator?  A simply loose wire (and alternators and engines VIBRATE  a lot) could do what you are describing as intermittent failures.

Could there be a link to this very recent thread?  (Engine Dies at Low Idle): http://c34.org/bbs/index.php?topic=3869.0

[Wayne]

I'm having a like problem on a 2006.  On mine, when motoring at about 2800 RPM my tach will sometimes jump to 3400-3600 and stay there for awhile. 
Dealer is still tinkering . . .

[Stu Jackson]

Loose belt?  Have you bought an alternator belt tensioner?  See: http://c34.org/bbs/index.php?topic=3667.0

Use the link in that thread for the source.

[David Arnold]

I too have been having faulty readings with the tach on my 2005 (hull 1707).  Basically at anything more than an idle the tack pegs out at max RPM.  The engine is running like a top but I just can't rely on a reading from the tach.  When the problem first started a few weeks ago I banged the dial with my knuckle and voila, the tach registered correctly.  That was short lived and new it just stays pegged at max.  If there is a connection with the alternator belt tension, I am on my second belt which is as tight as I can make it but there is more than 1/4 inch deflection and I am up against the stop on the adjustment bolt.  The new belt is the same number as the old but I am thinking that perhaps the replacement belt has somehow stretched and should be replaced again.  Any thoughts would be most appreciated...

[Stu Jackson]

I didn't intend to suggest over tightening the belt, just wondered if that could be the cause.

Since the tachs work off the alternator, there are only a few things to check.  If a dealer was doing it, so could you.

1.  The connection at the alternator is bad, simple to check.

2.  There's something wrong with the wiring.

3.  The connection at the back of the tach is bad, simple to check or redo.

4.  There's something wrong with the tach, means replacement is needed.

Our boat has a combination tach and engine hour meter.  I've been looking in catalogs recently and haven't seen that particular combination unit, although I'm sure a check of the Teleflex website or a call to Seaward would turn them up.  Don't know if the Mark IIs have the combination unit.

Only other thing is something wrong with the alternator, which an automotive shop could easily check for you.

[Momentum M]

Guys...I'm also having the same problem but, I would say, only this summer.  Before I never notice anything strange.  That, I would think, would eliminate wrong connections as I never had to play/touch these wires. 
My boat is on hard from end of September to end of May (every year) and now I'm finishing my 3rd seasons.  Also, for what it's worth, I'm always in fresh water....so corrosion would be at a leaser degree.
I'm not to worried 'cause the sound of the motor gives me a good idea of it's revolution...not that I would mind having the real reading.
So Tommy's, Wayne's and David's stories are identical to mine...and strangely enough...of the same era ie: 2004/2005
Mine, 2005, hull 1719
Serge

[Stu Jackson]

Serge, it's not so much wrong connections as loose ones.

Also, I think it IS important to have a working tach, not so much to judge your throttle position or engine "comfort zone" but more importantly to assure that your alternator is working. (I rarely use the tach to set the throttle position, because I understand just like you that there are certain sweet spots that only each owner knows.  OTOH, it helps new crew if you say "advance throttle to 2200 rpm.")

We installed our new alternator/regulator last year.  There are a gazillion connections on the back of it, OK, OK, quite a few.

Of all the connections, each and every one of the factory-manufactured ring terminals / crimps / heat shrink catastrophically failed over the course of the past year.  One that I redid myself also failed - I gotta get better at that!!!

The ONLY way I knew immediately from the cockpit that wires had dropped off was that the tach stopped working.  Whether it's the ground or any of the positive wires from the ignition or the regulator, you NEED to know this.  If a ground and a positive broke off at the same time and touched each other it could be frightening.  If the positive wires that had dropped off had touched the case (even though the alternator is grounded by a wire it still goes to the same engine ground that the alternator case is strapped to) it wouldn't have been nice.

I have a backup place to check: with our new regulator, which has lights, I check it even though it's under the head sink.

If you have an OEM internal regulator, while you may have less chance to have loose wires from the back of your alternator, it can still happen and the only measures of knowing that your alternator is still working are the voltmeter and the tach.

You could be motoring for hours depending on your alternator to charge your batteries.  No tach, no knowledge.  The analog voltmeter on the cockpit panel is NOT all that sensitive.  Your boat, your choice.

PS - The only gage I'm comfortable with NOT working is the fuel gage.  See: Fuel Log - http://c34.org/bbs/index.php?topic=3841.0

[tonywright]

Maybe this is crazy , but I had a thought:

While I haven't experienced your problem, I did notice my tach had condensation on the inside of the glass one day.   What I did was turn on the nav lights (in the middle of the day). My theory was that there is probably a light bulb in there somewhere that will generate some heat, and dry it out. It worked.

So here's the thought: If tapping the glass fixed the problem once, any chance that moisture in the tach electronics is causing the problem? Anyone tried turning on the nav lights for a while to see if it dries out and gets rectified? Next step would be to find out how to stop the moisture getting in! Maybe this has to do with a less than perfect seal around the engine panel box?

As I say, maybe this is crazy ...

Tony

[Gary]

Until this weekend. Start the engine and at what I know is 800-1000 RPM idle it reads 3000 RPM. Hit the throttle a little and it pegs. Three days out, same thing.


Had a similar problem.  Opened the engine panel tightened and cleaned the connections on the tach/hour meter.  I think the real problem was that the tach internal light was loose (it is a press and twist fitting) and the light with engine vibration was going on and off.  Perhaps that irregular voltage was effecting the reading.  No problems since fixing and tightening the internal light.

Be sure to let us know if any of this helps!

[Ron Hill]

Tom : Pickup the telephone and give Teleflex a call, they'll take the symptoms and tell you what to check. I'm traveling and don't have their # handy, but it's listed here on our web site.