Erratic tach readings

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

Erratic tach readings

Postby ericinga » Mon Jun 06, 2016 6:47 am

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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Location: Rock Halll, MD
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Re: Erratic tach readings

Postby Fastjeff » Mon Jun 06, 2016 11:13 am

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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Joined: Mon Jul 14, 2014 11:21 am
Location: Cumming, GA

Re: Erratic tach readings

Postby ericinga » Mon Jun 06, 2016 11:57 am

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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Joined: Mon Jan 19, 2015 11:07 pm
Location: Lake Superior-Michigan's U.P.

Re: Erratic tach readings

Postby TinLizzy » Mon Jun 06, 2016 6:27 pm

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, Raw Water cooled
Portage Canal Waterway-Upper Peninsula,Lake Superior

Fastjeff
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Re: Erratic tach readings

Postby Fastjeff » Tue Jun 07, 2016 5:04 am

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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Location: Grosse Ile MI

Re: Erratic tach readings

Postby bill » Wed Jun 08, 2016 6:52 am

BigM
A dead blow hammer :roll: is a handy tool :!:
:lol:
bill ;)
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

Third Owner bill

Fastjeff
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Re: Erratic tach readings

Postby Fastjeff » Thu Jun 09, 2016 5:16 am

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