Erratic tach readings

A/C & D/C Wiring, GPS, Radios, etc.
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ericinga
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Posts: 170
Joined: Mon Jul 14, 2014 11:21 am
Location: Cumming, GA

Erratic tach readings

Post by ericinga »

Unravelling the mysteries of a new to me boat.

Tach readings were almost unusable a few weeks ago. Port motor read 3K RPM at idle. Starboard bounced around at 3K plus.

I cleaned up all the grounds in the bilge and coated with dielectric grease. Cleaned all ignition connections at the motors. Found the ballast resistors were bad which was causing the ECM to overheat and the potting to melt. Replaced the ECMs and resistors both motors. For grins, I replaced the starter solenoids. Had two in the spare parts bin.

Found the stereo and four other 12V accessories were grounded to the voltage gauge at the lower helm. Rerouted these wires to the grounding bar under the helm.

Anything other places to look?
Eric Spies
1989 32 SDFB
Twin 318s
Lake Lanier, GA
Marinette Boat
Fastjeff
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Joined: Sat Jul 12, 2014 5:06 am
Location: Rock Halll, MD

Re: Erratic tach readings

Post by Fastjeff »

SOME tachs have an adjustment in the back for the number of cylinders, 2 vs. 4 stroke, etc. IF yours has this, use a small screw driver to push IN then turn the adjustment back and forth a few times to clean the contacts.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington
ericinga
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Posts: 170
Joined: Mon Jul 14, 2014 11:21 am
Location: Cumming, GA

Re: Erratic tach readings

Post by ericinga »

Jeff-

These tachs do have a cylinder selection dial. I looked at it, saw it was set at 8 and left it alone.

I'll twist it a few times.

Thanks

Eric
Eric Spies
1989 32 SDFB
Twin 318s
Lake Lanier, GA
Marinette Boat
TinLizzy
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Posts: 263
Joined: Mon Jan 19, 2015 11:07 pm
Location: Lake Superior-Michigan's U.P.

Re: Erratic tach readings

Post by TinLizzy »

Give the tach a wrap with your knuckles when they start to act up, sometimes it takes a couple hits. If they straighten out, replace them, they are on their way out. I have done this on many over the years, and do it on my port tach also, it hangs up around 2000, a quick tap and it returns to normal.
Rodney
1975 28 Express-Twin 350 Chevy's, SOLD
1990 32 Express--Twin Mercruiser 454 with Bravo I outdrives
Portage Canal Waterway-Upper Peninsula,Lake Superior
Fastjeff
Site Admin
Posts: 1520
Joined: Sat Jul 12, 2014 5:06 am
Location: Rock Halll, MD

Re: Erratic tach readings

Post by Fastjeff »

Like they do in the submarine movies!

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington
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bill
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Posts: 520
Joined: Sat Jul 12, 2014 7:17 am
Location: Grosse Ile MI

Re: Erratic tach readings

Post by bill »

BigM
A dead blow hammer :roll: is a handy tool :!:
:lol:
bill ;)
Former owner of
ALUMINATION
Grosse Ile MI
Located on LakeErie
37' F/B Sedan
1975
Twin 360 Chrysler Marine
Raw water cooled
Hydraulic steering both helms
USCG Master Lic. Retired[/color]
Third Owner bill
Fastjeff
Site Admin
Posts: 1520
Joined: Sat Jul 12, 2014 5:06 am
Location: Rock Halll, MD

Re: Erratic tach readings

Post by Fastjeff »

Fastjeff Rule # 1: If it won't move, get a bigger hammer.

My Mom was in my garage once and noticed the letters "BFH Dept" on a drawer my tool box. (Hint: The "H" stands for "Hammer") Had to do some fancy footwork to get her attention focused elsewhere.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington
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