Jumpy Tachometer

[gmilburn]

Hi all,

A few weeks ago, I installed all new gauges for my Atomic 4 on my 33 year old Ericson 29. I rewired all of them from the cockpit to the engine. I was thrilled when the engine started and all my gauges produced readings. However, my tachometer reading is jumpy, but does not necessarily coincide with an engine miss (but it is hard to really tell!). I have posted a short video of the tach problem on youtube:

http://www.youtube.com/watch?v=IWirmCPQVeM

It happens at all speeds, but does not seem to affect either the power (boat speed) or starting (it has always started within a second of engaging the starter). Any idea what the problem is? I believe it is a momentary short or electronic glitch that I would like to identify and fix--before it perhaps leads to bigger problems.

Any help or advise would be appreciated.

[baileyem]

jumpy tach

It looks like you are getting readings on the tach of about twice what they should be. Idle speed should be less than 1,000 and it doesn't sound like you are winding it up to 2,500+ . make sure that you have the connections correct for a 4 cylinder engine.

I agree with you that it must be something other than fluctuating engine speed making it jump. Your engine sounds great.

Good luck.

Mike

[Kelly]

I would just second what Mike wrote. From the sound of your engine (great video, it really helps) you are indeed far from running at 2000 rpm. I would suspect the "jumping" of the tack readings is also due to a wiring problem or adjustment problem in the tack.

Kelly

[roadnsky]

Did you run NEW wiring or use existing wires?
14 gauge wire? Good solid connections on the coil?

If you bought the ISSPRO gauge from MMI they usually come pre-set for the A4 (4 cyl) but I agree you should double check that jumper on the back.

Nice gauge package, BTW!

[gmilburn]

Thanks for all the helpful suggestions and comments.

Yes all gauges came from Moyer Marine--and I am fairly confident that I checked the jumper and made sure it was set on 4 cylinders rather than 6 or 8--but will check again. I agree it seems that the rpms seem high.

I used new 10 gauge wire for the ammeter and 12 gauge for all others. I will check the terminals and connections again--and perhaps use a jumper (outside the cockpit) from the tachometer to the coil to make sure that the new wire is good.

I'm beginning to think the tachometer itself might be bad.

Any other thoughts?

Gary

[Kelly]

archived advice

Gary,

Please bear with the "obvious" advice but this might help in your trouble shooting. Don explained in a previous post "The red wire connects to switched DC power (like the ignition switch), the black wire to ground, the white wire to the negative of the coil, and green to the switched lead from the light switch."

If all that checks out, then perhaps you are correct in thinking your gauge has an internal problem.

Kelly

[alberg]

If you have a distributor with points I would look for contact bounce or a bad capacitor. The tach would show multiple make/break cycles that the coil or engine would not respond to. The same effect may also be occouring with an electronic ignition system.

Alberg.

[roadnsky]

Thanks for all the helpful suggestions and comments.

Yes all gauges came from Moyer Marine--and I am fairly confident that I checked the jumper and made sure it was set on 4 cylinders rather than 6 or 8--but will check again. I agree it seems that the rpms seem high.

I used new 10 gauge wire for the ammeter and 12 gauge for all others. I will check the terminals and connections again--and perhaps use a jumper (outside the cockpit) from the tachometer to the coil to make sure that the new wire is good.

I'm beginning to think the tachometer itself might be bad.

Any other thoughts?y

Gary-
Did you ever solve this issue?
The reason I ask is that I replaced my small TACH with the exact same one you have (I wanted the larger face) and guess what?
It's jumping too. Exactly like in your video.
My RPM's are reading correct (almost exact to the previous gauge)
It doesn't "jump" until the alternator kicks in. Before that it is smooth.
The moment the voltmeter shows the alt start up, the jumping starts too.
(Also, I have electronic ignition)

I'm going to run some voltage readings and various re-wiring experiments today, but thought I'd revive this thread and stir the pot while everyone is home too full of turkey and nursing hangovers...

[roadnsky]

Ok, need some opinions and help from you guys...
I ran some tests and checked wiring on this and I can't figure it out.
Voltage readings at the battery, starter, coil and alt all seem right.
I ran jumpers to bypass NEW wiring, still the same issue.
Triple checked the wiring. It's wired correctly.

The 'jumping' is for sure starting the moment the alternator kicks in.

Any ideas of something I'm missing?
Faulty tach or should I start suspecting the alternator?
(Rigs, Steve you out there?)

[Don Moyer]

Jerry,

I've been suspicious of the fact that your tach becomes jumpy only when the alternator comes on line, but with your voltage indications remaining normal I fail to see how that fact relates to your situation. Pending a more reasoned response from Rigs or Steve, it's probably time to consider another tach. If you give me a call at our tech service line (410-810-8920) we can work something out in that regard.

Don

[sailbristol]

jumpy tach

make sure your alternator belt is the correct tension,otherwise you will get random voltage fluctuations that can cause your problem

[roadnsky]

make sure your alternator belt is the correct tension,otherwise you will get random voltage fluctuations that can cause your problem

Hmmm, good point. I doubt it's loose, but I'll check it today.

Don,
I'll check the belt and give you a call tomorrow.
That might give Rigs and Steve (or others) a bit more time for any ideas.

Thanks guys!

[rigspelt]

That might give Rigs and Steve (or others) a bit more time for any ideas.

Don't interpret my posts to suggest I'm any kind of expert. The only time I've encountered a jumpy tach was on on a twin-engined powerboat we used to have. One of the tachs started jumping like that intermittently one season, very infrequently. A couple of years later the engine cut out during the jumping, which had become more frequent. Tore my hair out (figurtively) chasing that gremlin down. Several hundred dollars and year later, it turned out to be a $30 slave starter solenoid. There was a cold connection inside that failing unit: the engine would cut out after about 45 minutes of running when the solenoid got warm, and then restart after it cooled, then quit again.

I guess based on that experience, I'd start looking at any devices in the circuit like a solenoid or something else with hidden electrical connections. Just because I have no idea, I might take that alternator to a shop and see if they can detect any irregularity in its electrical field while running, but any part in the circuit could be contributing. If you get into swapping parts, start with the cheapest ones.

I presume you've done googling on jumpy tachs. I haven't done that in the past few years, but back then there were lots of stories for boats and cars, and there were lots of different causes. But there are principles for tracking it down.

[roadnsky]

Thanks Rigs.
You're still one of our resident experts whether you like it or not...

I'm gonna try the belt today, 'cause the more I ponder it, the more it makes sense.
I'll report back...

[sastanley]

compare?

Jerry, I have a spare alternator that I got from a Catalina 30 buddy that foolishly swapped out the A-4 for some noisy diesel years ago....I'd be happy to send it to you for testing and run a comparison on your engine..I'd like it back some day though...I don't expect to fire up the boat again until March or April.