Tach readings erratic

[Bob Fort]

The tach on my 1998 Volvo Penta 135 hp gas engine in my Glastron GS185 is giving me very erratic readings although the engine seems to be running OK. Any suggestions to start my troubleshooting?

 

[pdecat]

look for loose or corroded connections.

 

[rnbenton]

What Bruce said. Any and every tach problem I have ever had was caused by a loose/corroded ground wire.

Bob

 

[cmariner32]

A lot of tachs have a setting on the back to switch from 4-6-8 cylinder engines or a calibration adjustment. Exercising the settings adjustment-switching thru the different settings will sometimes correct the reading. I have to exercise the tachs on my really old boat several times during the season-I consider it part of my normal maintenance.

 

[easttnboater]

What cmariner32 said. I have even soldered around the switch to keep from having this problem.

 

[Harlan]

I have had two on Sea Rays that had erratic readings. The needle was loose an the shaft. Carefully took the face off the tach and glued the needle.