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Tachometer not reading properly

G

gamparano

New member
1986 Riviera Ebbtide 4.3L OMC Cobra. Have a 14 1/4 X 17 prop. When idling the tach reads between 600-700 RPM. The engines runs like a dream. Starts right up, no problems. Checked wiring on Tach. Grounds are good, hot is good, sender good. Get it on the lake and when I go to almost WOT the Tach will read about 3000 RPM and the engine is reving loud. The boat is probably moving about 40-45 mph (can't decipher to knots). I looked on the back and put the dial on 6 cyclinders is this right for my 4.3L OMC Cobra? Maybe a new Tach? Help please. Any other way to test the Tach for accuracy? Thanks.
 
If it is original, it has probably suffered internal corrosion and should be replaced. Many times, you can get temporary relieve by cycling the cylinder count switch back and forth many times.

As far as testing goes, there are 3 ways I know of: 1) known good shop tach used as a reference, 2) a " tach tester" - self contained electronic box that generates pulses similar to the ignition coil, & 3) an optical (non-contact) tach used to read rpm from the crankshaft.
 
I've been through this nightmare before as well! I finally said to hell with it and bought custom gauges from Ocean Gauges[/URL] You can purchase any amount of gauges that you need and calibrate them for both your tach and tank size."]Ocean Gauges.com They're really accurate and you can calibrate them to just about anything.[/URL]
 
TACH PROBLEMS:
Hopefully, I'm doing this right

1991 Johnson 150GT
OMC Tach
Voltage regulator replaced 2010, <30 hours on it
Wiring checks ok.

1) Tach is intermittent
2) When it is working, drops to zero as soon as it reaches +/-2700 rpm

Thanx!
 
bajaskier said:
TACH PROBLEMS:
Hopefully, I'm doing this right

1991 Johnson 150GT
OMC Tach
Voltage regulator replaced 2010, <30 hours on it
Wiring checks ok.

1) Tach is intermittent
2) When it is working, drops to zero as soon as it reaches +/-2700 rpm

Thanx!
Click to expand...

Ayuh,.... Yer close,....

Start a thread of yer own, insteada hi-jackin' a 3 year old thread,....

Start yer own thread in the Johnny-Rude Outboard forum insteada in this forum,....
 
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