Association Forum - Tachometer working intermittently

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Tachometer working intermittently

New Topic

Topic Locked

Printer Friendly

Author

Topic

SKS
Navigator

Member Avatar

USA
161 Posts

Initially Posted - 07/03/2016 : 06:33:42

OK, I've replaced the starter button. Now the engine turns over immediately.
When the enginte starts, the tach reads 0.
If I gun the engine, the tach suddenly springs to life.
This seems to happen consistently.
Does anyone have any idea why this is happening ?
Do I have a potential problem with my alternator ?
Or is this just a corroded wiring issue ?
I'm going to do the renaming ceremony tonight. Maybe that will fix the problem.

"Lady E" 1986 Catalina 25: Fin Keel, Standard Rig, Inboard M12 Diesel, Sail No. 5339
Sailing out of Norwalk Cove Marina, Connecticut

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9013 Posts

Response Posted - 07/03/2016 : 08:16:16

Not many inboard diesels among us here, but maybe somebody knows... Sounds to me like a sticky gauge--a little extra push gets it going. But I don't even know how a tach works on a diesel, with no ignition system. My tach (Honda V6) is spasmatic--often jumping to double the RPMs and then back, and shows signs of moisture inside. I was more worried when my fuel gauge went out, which I fixed. (Fuel is more critical to me these days.

)

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

sethp001
Mainsheet C-25 Tech Editor

Members Avatar

814 Posts

Response Posted - 07/03/2016 : 08:51:29

In addition to what Dave said, corroded or loose wiring are a likely cause. Look especially for a loose or corroded ground connection, which is a common point of failure.

A reason why gunning the engine can cause the tach to "spring to life" is that the loose or corroded wire increases the impedance in the circuit between the sending unit and the gauge. The voltage generated at the sending unit varies with engine speed. At low engine speed, the voltage is not great enough to overcome the impedance in the circuit, no current flows, and your tachometer reads 0. The higher engine speed causes the sending unit to generate a higher voltage that can overcome the impedance in the circuit, current flows, and your tach springs to life.

It is possible that the loose connection or corrosion are in the tach itself, but the principle behind the issue is the same.

If its not a bad gauge or bad wiring, check the sending unit and the alternator.

Let me know if you want/need more specifics for troubleshooting.

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

Edited by - sethp001 on 07/03/2016 08:54:00

SKS
Navigator

Members Avatar

USA
161 Posts

Response Posted - 07/03/2016 : 10:16:01

quote:
Originally posted by sethp001

In addition to what Dave said, corroded or loose wiring are a likely cause. Look especially for a loose or corroded ground connection, which is a common point of failure.

A reason why gunning the engine can cause the tach to "spring to life" is that the loose or corroded wire increases the impedance in the circuit between the sending unit and the gauge. The voltage generated at the sending unit varies with engine speed. At low engine speed, the voltage is not great enough to overcome the impedance in the circuit, no current flows, and your tachometer reads 0. The higher engine speed causes the sending unit to generate a higher voltage that can overcome the impedance in the circuit, current flows, and your tach springs to life.

It is possible that the loose connection or corrosion are in the tach itself, but the principle behind the issue is the same.

If its not a bad gauge or bad wiring, check the sending unit and the alternator.

Let me know if you want/need more specifics for troubleshooting.

I've disassembles and cleaned up the connections at the back of the tachometer. No joy. I get the same behavior. I have no idea where the other connections are, or I'd clean them as well.
I would very much appreciate an idea of how to troubleshoot and solve the problem.
I suspected some sort of issue involving corroded wires.
I have access to industrial grade contact cleaner and can spray it where necessary.
My main concern was a problem with the alternator itself.
If the tach doesn't read accurately, but the alternator is still charging, then I'm OK with taking some time to repair the tach.
It's been said many times. Salt water and electronics don't mix well.

"Lady E" 1986 Catalina 25: Fin Keel, Standard Rig, Inboard M12 Diesel, Sail No. 5339
Sailing out of Norwalk Cove Marina, Connecticut

OJ
Master Marine Consultant

Members Avatar

USA
4382 Posts

Response Posted - 07/03/2016 : 10:36:43

Are you literate with a multi-meter?

If you replace any wiring I suggest using ANCOR

http://www.ancorproducts.com/en as each strand is tinned.

I would also recommend using crimp connectors that incorporate heat shrink tubing

http://www.ftzind.com/store/main.aspx?p=PictureListBody&c=WTCR

Since inboards are in the minority here - I suggest you try

http://www.sailnet.com/forums/

Similar to the Catalina 25 forum - there are a great group of experienced sailboat owners there wanting to help.

1989 C25 TR/WK, #5822
1973 McVay Minuet 19
1975 Jester 12
1981 C25 SR/SK, #2428
1981 C22 SR/SK,
Tanzer 16
Sunfish

"There is nothing, absolutely nothing half so much worth doing as simply messing about in boats." Kenneth Grahame

Edited by - OJ on 07/03/2016 10:44:06

hewebb
Admiral

Members Avatar

USA
761 Posts

Response Posted - 07/04/2016 : 03:53:44

When I got our boat the engine wiring was a mess and had some intermittent issues. I replaced nearly all of the engine wiring and now all is well. I suspect that there were some splices that were an issue. I think I would remove the alternator and have it bench checked or attach a meter to the tach out put terminal and take readings at various RPM.

1988 WK/SR w/inboard diesel Joe Pool Lake
Hobie 18 Lake Worth

Life is not a dress rehearsal. You will not get another chance.

sethp001
Mainsheet C-25 Tech Editor

Members Avatar

814 Posts

Response Posted - 07/04/2016 : 10:00:22

So I read through the service manual for your engine last night. Your engine does not use a separate sending unit. Instead, the alternator itself functions as the sending unit. The manual does not have a test procedure for diagnosing tachometer problems, so I made a test procedure for you below.

ALTERNATOR WIRING DIAGRAM:

IMPORTANT NOTES:

Use an analog multimeter for this procedure because the AC TAP pulses DC, which some digital multimeters will not "see". If you don't already have one, you can get one for about $20 at a hardware store.

***Even though you'll be testing the AC TAP, test for voltage using the DC mode only. ***

*** Make all tests for resistance with the engine and all electrical systems off.***

PROCEDURE:

1. On the alternator, make sure you have a good connection on the wire marked AC TAP (TACH) in the diagram.

2. With the engine running at idle, measure the voltage between the AC TAP (TACH) and the GROUND posts on the alternator. You should see a voltage, probably around 7V. If you see no voltage, than the alternator is the problem. If you see voltage, continue to next step.

3. With the engine idling, at the back of the tach, measure the voltage between the connection from the AC TAP and the negative/ground connection. Then measure the voltage between the positive connection and the negative/ground connection.

If the AC TAP voltage is the the same as it was at the alternator AND the positive connection voltage is around 12V, then the tach is bad.

If the AC TAP voltage is less than as it was at the alternator AND the positive connection voltage is around 12V, then the AC TAP wire/connection is bad. Confirm by measuring resistance between the AC TAP connection on the tach and the AC TAP (TACH) post on the alternator.

If the AC TAP voltage is less than as it was at the alternator AND the positive connection voltage is less than 12V, then the ground wire/connection to the tach is bad. Confirm by measuring resistance between ground connection on the tach and the black wire on the negative battery terminal (There may be more than one black wire there, so you may have to visually confirm you have the right one. Also, your PO may have changed the wiring, added a bus bar, etc., so you may have to follow the ground wire back.)

If the AC TAP voltage is the same as it was at the alternator AND the positive connection voltage is less than 12V, then the positive connection is bad. Confirm by measuring resistance between positive connection on tach to post with purple wire on back of alternator.

OTHER IDEAS:

Below is a wiring diagram, which shows a couple of wiring harnesses and connectors between the engine and instrument panel. Those connectors are likely points of corrosion. You could try to isolate the problem more than I did in the procedure above by testing the resistance of the wires between the connectors, from the connectors to the end points, etc. Note that the AC TAP wire from the alternator to the tach does not go through those harnesses or connectors.

Stu Jackson C34
Admiral

Members Avatar

844 Posts

Response Posted - 07/04/2016 : 11:53:22

Your alternator could be grounded to the engine from its bracket. That could be an issue. Check the bracket connection, which could well be on top of paint. A better solution is to add a ground wire from the alternator to the main engine ground.

Most of the Catalinas have trailer wire connectors in the wiring harnesses. These are notorious points of failure and have been forever. Here are some stories: http://c34.org/bbs/index.php/topic,5078.msg44056.html#msg44056 Wander around that thread, there are more than one posts on that topic.

Check the wiring AT the tach. Every wire has two ends.

Good luck.

Stu
1986 C34 #224 "Aquavite"
Cowichan Bay, BC Maple Bay Marina
(formerly San Francisco)
(formerly C25 #2459 "Capricorn Two")

SKS
Navigator

Members Avatar

USA
161 Posts

Response Posted - 07/05/2016 : 16:55:21

Thanks to all.
One thing I neglected to clarify. This is a new issue. The tach worked fine all last season. It only became intermittent this past week.
In it's prior life, the boat lived on the Hudson, predominantly fresh water.
Now the boat lives in the salt water of Long Island Sound.
Something changed, either terminals became corroded or a device is beginning to fail.
I don't believe there is a design flaw, or the tach would never have worked correctly.

Again, thanks for all your help.

"Lady E" 1986 Catalina 25: Fin Keel, Standard Rig, Inboard M12 Diesel, Sail No. 5339
Sailing out of Norwalk Cove Marina, Connecticut

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.