Tachometer Failure where to Start?

[Captain PartyMarty]

My new boats tachometer doesn’t work, I figured it was just a corroded connection problem but after checking the back of the gauge I can find anything wrong with it. Do any of you have a suggestion about where to start in trying to diagnose the problem? Currently the needle sits below zero RPM and doesn’t move when the key is turned. I am pretty sure ECU is working right because the boat surveyor was able to read RPM on his labtop when connected to the engine. Either the Gauge or wiring is hooped. Any ideas on how to test the gauge?

The gauge is a multi-gauge from Mercury

The engine is a 2005 135hp Optimax

 

[Gunsmith]

My E-tec did that once and I was totally lost. Had power and all looked good, so out of lack of anything better to do I gave the tach a hard slam and presto the needle was stuck and it started working. Worth a try just don't break the glass.

 

[trendsetter]

Could be as simple as a fuse somewhere on the line from the ignition to the tach. When you turn the key to the on position 12v is applied to the ignition terminal on the back of the tach. This should make the tach zero out. If the tach doesn't do anything when you turn the key then either it is faulty or the 12v connection to the ignition terminal is not being made. This could also be due to a bad ground connection on the tach.

 

[salmonkiller01]

Do you have the smartcraft gauge with all the engine info on the lcd below the tach? Wont be any fuses, the tach gets all its info from the pcm. Try unpugging the tach and plugging it back in.

 

[Captain PartyMarty]

No Smart Craft, but thinking this gauge is dead I might upgrade the tach to SmartCraft

 

[salmonkiller01]

Its worth the upgrade to smartcraft, you get all you engine info, hours, temp, water pressure, faults, fuel gph. One you figure out which gauge you need( part number for your specific engine) ebay has the best prices, about a 1/3 of canadian prices.

 

[marula]

Captain, most tachs get their signal from the charging coils and can be indicative of a bigger problem. Sugguest getting a voltage meter on the battery with motor not running then when running. If your not seeing higher voltage around 13.5 to 14.5 then you may have a charge problem. That should be the first test as you dont want to be out on the water with no charging. My tach would jump around then zero out, diode fried in the regulator/rectifer box. Replaced that and tach worked properly again.

 

[adrianna3]

Mine quit and it turned out to be a shot rectifier on my Evinrude.

Dave

 

[Captain PartyMarty]

I thought the charging coils issue was limited to older motors but maybe not. I will check the voltage on the weekend, Thanks for the tips everybody

 

[marula]

Actually on your opti you are right that you have an alternator and i believe the tach signal comes from the regulator on the alternator and not the charge coils. Being a simple test i would still do this first incase your regulator failed. Lets us know how it turned out.

 

[Labman2]

If I read this right, the surveyor had a tach report through the info terminal, yes?
If so, it can't be the reg/charge coils, it has to be the wiring or a fuse, IMO.

 

[Captain PartyMarty]

Yes he did have a reading. I am starting to think its the tach, I think I am going to upgrade to a Smartcraft Tach. the extra features seem well worth the effort.

 

[salmonkiller01]

heres a link for smartcraft info. http://www.mercurymarine.com/media/mercury/documents/SmartCraft_Gauges_Owners_Guide.pdf

 

[combover]

get a test light make sure the purple wire is suppling power to the 12v connection when the ignition is on, then make sure it has a ground. next is the signal i think your best bet there is to check though the manuals to see if there is a spec on the opti's for the tach signal wire and routing. for me i would just hook up a working old tach with jumpers and if it works its your tach.

 

[wstcoaster]

on my honda the tach quit workingbut the trouble was in the charging circuits for battery fixed the charger tach was okay

 

[Captain PartyMarty]

Just got a wicked deal on a Smartcraft Tach in an ebay auction.

 

[sly_karma]

This.

No point in replacing gauge if no signal is reaching it. Read with multimeter at gauge, then go to sender at engine to eliminate a wiring problem.

 

[Captain PartyMarty]

Smartcraft install replaces exsiting analog cable with a Can Bus harness. Sincethe Surveyor was able to read the engine RPM with his labtop I am pretty sure this will fix the issue aswell as provide me with a bunch more information about the engine and how its running. Really looking forward to get started with the install

 

[Captain PartyMarty]

Got my new smartcraft gauge up and running last night. Can't believe how easy it was and by doing it myself and ordering the parts in the states I got it done for 350 bucks compared to the quoted cost without installation at a local marine store of 900 bucks. I am always amazed at how much information and diagnostic help can be found on the internet, it really empowers the do it your selfer!