Tacho Help/Advise

[pyro225]

Hi Guys,

Not sure if this should be in the mercruiser section or the diesel section.

Anyway I will start...

My tacho is on its way out it seems to be going nuts... when I start it idles anywhere between 4-5k (its not idling at that but tach says it it) it will jump around as you drive.

Anyway its on a mercruiser 1.7 dti io and normally I know diesels are meant to have a special tach, however this looks like a tach for a gas I/o - is this possible/correct? I cant get this tach anymore so want to make sure I buy the correct kind so any help would be great - pics below:

Thanks

MODEL: FARIA TC9384A (I believe)

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[JoLin]

See the screw at the bottom to the left of the column of numbers? Take note of where it's set now (which number it's pointing to), then turn it back and forth a couple of times. Now set it back to its original position. Sometimes that 'pole selector switch' (the screw) develops some corrosion around it. Exercising it a bit breaks it loose and returns the tach to normal.

That's not always the problem, but exercising the screw has fixed a 'wacky tach' on 2 of my boats.

 

[pyro225]

ok will give it a whirl - that fixed the bulb in it earlier - with regard to it being gas or diesel what do you think?

 

[alldodge]

ok will give it a whirl - that fixed the bulb in it earlier - with regard to it being gas or diesel what do you think?

A diesel gets its pulses from the alternator instead of the coil. Most any tach should work, and also keep in mind that a loose alternator belt can also cause the tach to act up

 

[pyro225]

Ok cool also my speedo doesn't work is there a quick fix for that?

 

[alldodge]

Ok cool also my speedo doesn't work is there a quick fix for that?

The speedo works off of water pressure. The drive has a 3/16 hole in the forward edge, many times a piece of wood or crud gets the whole filled up. Take a drill bit and clean out the hole by hand, don't use the drill. This tube goes thru the drive and is connected to a rubber tube under the exhaust bellows which then goes thru the transom plate and into the boat.

 

[pyro225]

I did the screw wiggle it didn't work I did it more still didn't then clicked to the next number... tada (although it seem accurate not sure its 100%)
This speedo hole - can it be checked while in the water? Also sorry if this is stupidly dumb - if my tranducer is in the hull does it have to come out to be changed?​

 

[tobyguy]

Emptying out crud from the speedo hole is emptying out crude (shouldn't matter if you do it on land or water). Though you will likely have to get in the water and put on a pair of goggles to see what you are doing (and confirm something was in there). You can use a drill bit and turn it by hand (do NOT use a drill), it's just to get whatever is stuck in there out (if anything).

I had to do this a few weeks ago (in the water). Didn't fix the issue for me though as I then realized the speedo tube connection had been re-wired to a wheel type device right at the bottom edge of the boat. I bought the boat off of a guy on a lake that has a lot of weeds and growth on it so I believe he got it changed likely due to it getting clogged all of the time.