tach, fuel consumption gauge readings

[dogdoc]

Had the engines tuned up recently when boat was up on blocks. New plugs, filters, O2 sensor, thermostat, etc. Boat ran fine on the way home from the boat yard, no issues at all. Sat for a few weeks and we went out fishing yesterday. Noticed right off the bat Port tach reading was all over the place from zero to normal, I say normal because the engine sounded fine and was running fine and the sync function was working and I could sync the engines easily. We were out all day and sometimes it would read fine for awhile then go batty. Also the fuel gal/hr reading for that motor was usually absent, ie no reading. When cycling the gauge from port to starboard to both, starboard was ok, port nothing and both same as starboard. On the way in the port engine did read normal fuel consumption for a short time but did quit again. Oddly out of the blue the mph reading came on, which has never worked since I've owned the boat. I believe this comes from the port engine as well. All the gauges were replaced 2 years ago and worked fine with exception of mph until now. I looked through the Seloc manual and cannot make any headway, really not sure how to trouble shoot this at all.
Any help would be greatly appreciated. Just to be clear the boat ran fine the entire day.

 

[seasick]

What style gauge? My initial though was a bad tach or hopefully an intermittent connection. Cheick ass connectors on the harness and grounds at the helm gauges. Maybe it's simple.
Regarding the speedo; Is the source of speed data the pitot hole on the lower unit or a speedo wheel on the transom?
Regardless, both sources can have issues and are usually inaccurate. Plotter GPS speed is much more accurate with the possible exception of trolling speeds. Do you use a troll feature where the motors adjust to maintain a set trollong speed?

 

[dogdoc]

digital gauges, 2 tachs, one speed, one fuel mgmt. oem yamaha gauges. speed is pitot tube pic below with port(problem engine) ignition on but not running. starboard only uses top left tach and supplies info to fuel mgmt gauge

 

[seasick]

Does the gauge self test on power up?
If not, check connections first. Although I usually don't like swapping parts, you might want to swap the tachs or if possible the rear harness connectors to see if the problem stays with the gauge (bad gauge) or stays with the engine ( bad connection or something else worse like a bad ECM).
I don't know if the power for the gauge comes from a fuse at the motor)

 

[Fishtales]

I'm in agreement to check the wiring. Maybe intermittent, something came loose or you had a small animal get in there. Check the engine side connections as well.

 

[dogdoc]

gauge does self test. pulled cowling and checked what i could see, have to admit hard to tell what is what. nothing looked amiss. same at back of gauge. did run the boat on the lift for 20 min and all seemed good. which did not instill much confidence as a come and go problem is worse. additionally the trim skeg on the starboard motor was gone again. this was replaced when blocked up and engine has 6 hours since install. did use blue locktight this time. it was an after market brand. thats 3 in the last few months and the shortest lifespan of any replacements. any ideas there?

 

[seasick]

I don't know why the tab (anode?) fell off but you should not have to use Loctite on those anodes. Too much is not good. Also note that if you tightened to spec with a torque wrench, the spec has to be adjusted when using a thread locker. The factory spec is for a clean dry assembly.
I would think that they were not tightened to spec assuming you don't have a serious vibration in the LU.
You probably should try a different brand.