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Old 29-08-2016, 09:01   #1
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Tachometer Fluctuates

Tachometer Fluctuates at idle and while in gear. Engine runs smoothly, normally and does not align with tach fluctuation. Started a few weeks ago. Is becoming less intermittent and is almost always now. Original Motorola tech. I've had her for 9 years over all.

1986 Young Sun Center Cockpit w. 80 HP 4 Cyl. Ford Lehman.

Alternator is less than 2 years old. Wiring "looks" solid.

- Any ideas on how to troubleshoot and or fix?

- Is this indicative of other problems?

- Is it ok to use until I find problem?



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Old 29-08-2016, 09:07   #2
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Re: Tachometer Fluctuates

I'd start with some 1000 grit automotive paper on each of those eight crimp terminals, plus the inline plug. It just sounds too much like a bad connection. Same for the back of the tach. Oh, and I'd give each wire a good pull to see if a crimp is loose.

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Old 29-08-2016, 16:20   #3
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Re: Tachometer Fluctuates

Also check to see if there is a sector switch on the back of the tach under that mounting plate to tell the tach how many cylinders you have. Our tach was doing just what you described, turning the selector switch back and forth a few times between 2 to 8 cylinders cleaned up the contacts and it immediately settled down when I switched it back to 4 again. Has been fine since. (4 years now)

Funnily enough, there was a comment in the survey that the engine idle speed was way too high at 1200 rpm. Of course, this was caused by the same switch playing up. Not so sure about the survey guy, it was pretty clear the tach was wrong to my ear.

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Old 29-08-2016, 18:11   #4
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Re: Tachometer Fluctuates

Sometimes its just a loose belt.
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Old 29-08-2016, 18:37   #5
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Re: Tachometer Fluctuates

Classic symptoms of a tachometer being run from the alternator stator output. Do you have an external alternator regulator by any chance?

Try increasing the dc load (turn on some lights) and see if the problem gets better.
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Old 30-08-2016, 04:48   #6
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Re: Tachometer Fluctuates

Greetings and welcome aboard the CF, JScotHuston.

Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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