Gauge issues- faria tach on a 1999 20' bow rider

[Augoose]

I'm having an issue that seemed to start all of a sudden last week - when the blower is on, the rpm increases by about 1,000 - 2,000 rpm. When I turn the blower off, the rpm goes back down to an accurate reading.
Then THIS week, the rpm would increase all on its own w/out the blower being turned on. Now turning the blower off and on seems to make no difference in the rpms.

During an inspection of the back of the gauge assembly, I couldn't find any loose wires, grounds etc, and none of the fuses are blown. I also can't see any corroded, worn or cut connections. Wiggiling the wiring harness seems to make no immediate change to the rpms on the gauge either.

Anyone have any suggestions? I was initially thinking bad gauge, however why would the blower effect it?
Thanks!

 

[Silvertip]

Re: Gauge issues- faria tach on a 1999 20' bow rider

Blowers are brush type motors and as such the arcing brushes can induce electrical noise in the power wires. If the power wires for the blower run adjacent to the power and "sense" wires for the tach it is very possible the tach is sensing those and hence the increase. In other words, you may have a "proximity" issue or you have a blower motor that is going bad due to excessive brush wear. This is a rather uncommon problem.

 

[Augoose]

Re: Gauge issues- faria tach on a 1999 20' bow rider

Thanks Silvertip. When tachs typically go bad, how do they go? Is the needle simply dead, does it miss-read actual rpms, or jumping issues etc?

 

[Silvertip]

Re: Gauge issues- faria tach on a 1999 20' bow rider

Thanks Silvertip. When tachs typically go bad, how do they go? Is the needle simply dead, does it miss-read actual rpms, or jumping issues etc?

Could be any or all of those things. They can stick, not respond, vary, etc. Its an electrical item with some mechanics. All of that is subject to failure from vibration, moisture, over voltage, under voltage etc.

 

[Augoose]

Re: Gauge issues- faria tach on a 1999 20' bow rider

Thanks. I'll trace the leads from the blower and tach to the cockpit, and look at replacing the blower and tach as well.

 

[mark1905]

Re: Gauge issues- faria tach on a 1999 20' bow rider

Check your engine compartment wiring harnesses for corrosion. Sounds crazy, but this reminds me of a whole host of gremlins that I was having surrounding blower operation and it all stemmed from the main molex being completely gunked up with corrosion and power and ground jumping all over the place.