Tach troublshooting

[Kyhl]

I have a faria tach in the dash connected to a Merc 115 4S.

Last year the tach would read funny. Example, it would occasionally read 1,500rpms low when crusing. Then the next run it would read normal.

Took the boat out Sunday and the tack does not respond. Usually when I turn the key it would bounce up and hold above zero even with the engine off. Now it rests on the peg at all times.

First question, is it possible that this is more than a tach issue?

If so, how would one troubleshoot it?

I did check for a loose wire under the dash and connections look fine.

Suggestions?

[fasternu]

I had this problem last year, when I took it in for a carb cleaning, the shop cleaned the connection at the motor and put so dielectric grease on it. Haven't had a problem since! I would start there first.

[Kyhl]

Well, that is good and bad news. Good that it's a cheap fix. I wasn't looking forward to replacing all the gauges when only one wasn't working. They have been redesigned since 2004 and it wouldn't look right having one of the current design next to a 10 year old speedometer.

Bad because I have no idea where the wire would be on the motor. Anyone know which lead on a 2004 Merc 4S runs to the tach?

Is there a way to attach a multimeter to the lead near the tach to verify if it is receiving a signal? I suppose I should also check to see if it is receiving power and ground while I'm at it.

[Kyhl]

Update, there is power to the tach so I guess it's time to order a new set of gauges.

Seems there is always something to fix.

[JohnMickish]

When you say there is power to the tach, do you mean there is a RPM signal or 12v power? Before I ordered parts I'd probably take it to a shop and see what they say.

[boatfixer]

When you say there is power to the tach, do you mean there is a RPM signal or 12v power? Before I ordered parts I'd probably take it to a shop and see what they say.

+1

It may be the signal that's not getting to the tach.

[JohnMickish]

That is what I was thinking. The 12v may just be the light power.

[Kyhl]

Checked three of the four connections, power, ground, and light.

I was not able to check the signal line.

When the power and ground are powered up the tach used to raise off the peg to above zero. Now it doesn't move.

Anyone have a suggestions for a trustworthy shop in the south west metro? I've already been burned this year with crappy and incomplete work from Rapid Marine in Shakopee. That will be another topic when I get the time. The more I dig into the work they completed the more problems I am finding. The short answer is, no one should ever bring their boat to them.

[Kyhl]

Update, I do have an older automotive multimeter that has a tach function. I will try hooking that up to the signal wire to see what happens. More to come later this week.

[wastewaterguru]

The tach feed comes off of the voltage regulator on most outboards that I have seen. I have seen several (Mercury especially) voltage regulators where the yellow stator wires that feed the regulator show signs of overheating. Once that start to happen, you typically see the result on the tach.

Regulators are designed to trickle current into the battery while running. The problem is that most boat owners have 15 accessories tied to their starting batteries. When the motor is started, the peak charging load from the partially depleted battery overheats the wires.

The voltage regulator should be considered in your list of things to check. Two yellow wires from stator under flywheel feed the regulator, which sends two red voltage wires to the starter solenoid typically to charge the battery. There is a black ground and a grey tach wire that come off the regulator. So to answer your question about where the wire comes from in the engine......it comes off of the voltage regulator (grey wire).

Best thing you can do for troubleshooting this is borrow a tach from someone and try it on your boat. Make sure the pole setting on the back are the same. I believe all the merc's are to be set at 6P./

[Kyhl]

Thanks for the info.

I'm preparing to leave on a four day trip, without the tach. Should I be concerned about the starting battery not being charged?

I do have a voltage gauge and will keep an eye on it. Last time out it hovered around 14.5v or so when running so I didn't notice anything unusual there. I also monitor the voltage through the HDS display which is coming off the starting battery versus wherever alumacraft has the gauge wired. The two read the same.

The good news is that batteries will be able to be recharged each night.

Guess I should set up an appointment somewhere for when I return next week.

[marine_man]

If you're seeing 14.5 Volts at mid to high throttle, you're regulator is charging your batteries correctly.

Have you verified that you have ground and power at the tach?

marine_man

[Kyhl]

Yes, ground and power to the Tach are live. I haven't tried testing the signal line.

Ran a seven or eight mile run to a gravel bar this morning and noticed after I arrived and turned the engine off that the tach had lifted off the peg. With the engine off it was sitting at 1k. I know it wasn't working the first mile from the dock. Didn't look at it again until after we stopped. Specifically checked it when we left the dock and the needle was sitting on the peg.

On the return trip, for the first mile, it gave a reading about 1,000 rpm low at WOT. As I approached the dock I noticed it was reading correctly again, actually my dad pointed it out. I was busy trying avoid debris and gill nets in the water while driving in the rain.

As expected, voltage read 14.5v on the gauge and the HDS when the engine was above idle.