Tach Anomaly
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Tach Anomaly
Coming home from a weekend on the water last Sunday and cruising at my normal 3600 rpm, I noticed the tach slowly creep up to 4000 rpm then slowly back to 3600 rpm. This condition repeated itself another 4 times before getting back to the marina. Although the tach was indicating a 400 rpm change, there was no noticeable change at the engine and no change in speed.
The tach is a Faria analog gauge and was new in 2001 along with all of the rest of the gauges. The distributor is the original Mallory with a Sierra electronic conversion kit that I installed about 6 years ago.
Any ideas on what may cause this?
The tach is a Faria analog gauge and was new in 2001 along with all of the rest of the gauges. The distributor is the original Mallory with a Sierra electronic conversion kit that I installed about 6 years ago.
Any ideas on what may cause this?
Paul
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB
Re: Tach Anomaly
I have the same gauges and about the same vintage. My starboard tach on the flybridge will do what sounds like the same thing. I give it a light knuckle rap on the glass face and it settles down.....not the best fix
but better (and cheaper) than replacing the gauge.
![Neutral :|](./images/smilies/icon_neutral.gif)
1972 Trojan Sea Raider F30 - FI 350's "Time Warp"
1998 Kawasaki ZXi 1100
1972 Chevy Fleetside Shortbed hotrod.......450hp
10.5 Newport Inflatable w/15hp Rude
1998 Kawasaki ZXi 1100
1972 Chevy Fleetside Shortbed hotrod.......450hp
10.5 Newport Inflatable w/15hp Rude
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Re: Tach Anomaly
Paul, look at the back of the tach and if it has a switch that you can adjust for 4,6 8 cylinder.......sometimes simply moving the switch around resolves this with some tachs( worked with mine)....maybe some kind of corrosion??....
Re: Tach Anomaly
Thanks gents, I'll check it out.
Paul
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB
- captainmaniac
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Re: Tach Anomaly
Agreed - crank the adjustment back and forth a few times to (hopefully) scrape away any corrosion that may be causing you trouble, then set it to calibrate it as needed.mikeandanne wrote:Paul, look at the back of the tach and if it has a switch that you can adjust for 4,6 8 cylinder.......sometimes simply moving the switch around resolves this with some tachs( worked with mine)....maybe some kind of corrosion??....
Not to hijack the thread, but on the same note as instruments not reading properly, had something weird happening to me on my vacation trip.
Stbd engine hours meter read exactly what it should, but for our last 2 runs port hour meter read 1 hour less than we actually did. Is this an electrical issue, or toasted gauge?
- prowlersfish
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Re: Tach Anomaly
Capt M you could be losing power or ground to your gauge I assume its a stand alone gauge ?
Boating is good for the soul
77/78 TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat![Very Happy :D](./images/smilies/icon_biggrin.gif)
77/78 TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat
![Very Happy :D](./images/smilies/icon_biggrin.gif)
- captainmaniac
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Re: Tach Anomaly
That's what I was thinking and will check it out, but power and ground are daisy-chained across all gauges (separate feeds for port and starboard of course) and the rest seemed fine.prowlersfish wrote:Capt M you could be losing power or ground to your gauge I assume its a stand alone gauge ?
Re: Tach Anomaly
Could be wiring or gage. I just replaced a gage that only recorded 3 hours on a 10 hour bench test.captainmaniac wrote:That's what I was thinking and will check it out, but power and ground are daisy-chained across all gauges (separate feeds for port and starboard of course) and the rest seemed fine.prowlersfish wrote:Capt M you could be losing power or ground to your gauge I assume its a stand alone gauge ?
She was a 1969 36 ft wooden beauty with big blue 440s that we'll miss forever.
And thanks to the gang, 2012 Trojan Boater Of The Year
And thanks to the gang, 2012 Trojan Boater Of The Year
Re: Tach Anomaly
Yep, pretty common symptom and fix. If that doesn't do it, look for a poor connection or if twins, try swaping units and see if the symptom follows the gage. Distributor issues usually show up as an erratic/fluctuating reading.captainmaniac wrote:Agreed - crank the adjustment back and forth a few times to (hopefully) scrape away any corrosion that may be causing you trouble, then set it to calibrate it as needed.mikeandanne wrote:Paul, look at the back of the tach and if it has a switch that you can adjust for 4,6 8 cylinder.......sometimes simply moving the switch around resolves this with some tachs( worked with mine)....maybe some kind of corrosion??....
Not to hijack the thread, but on the same note as instruments not reading properly, had something weird happening to me on my vacation trip.
Stbd engine hours meter read exactly what it should, but for our last 2 runs port hour meter read 1 hour less than we actually did. Is this an electrical issue, or toasted gauge?
She was a 1969 36 ft wooden beauty with big blue 440s that we'll miss forever.
And thanks to the gang, 2012 Trojan Boater Of The Year
And thanks to the gang, 2012 Trojan Boater Of The Year
Re: Tach Anomaly
I didn't have the opportunity to try this fix last year since the next time that I took the boat out the tach worked fine, and did up until this weekend. When I started the boat Friday morning to head out for the weekend, the tach was floating around at about 400-600 rpm higher than it should. When we came home Sunday, I rotated the switch back & forth between settings and the problem went away.mikeandanne wrote:Paul, look at the back of the tach and if it has a switch that you can adjust for 4,6 8 cylinder.......sometimes simply moving the switch around resolves this with some tachs( worked with mine)....maybe some kind of corrosion??....
Paul
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB