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Erratic tach readings

Posted: Mon Jun 06, 2016 6:47 am
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?

Re: Erratic tach readings

Posted: Mon Jun 06, 2016 11:13 am
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

Re: Erratic tach readings

Posted: Mon Jun 06, 2016 11:57 am
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

Re: Erratic tach readings

Posted: Mon Jun 06, 2016 6:27 pm
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.

Re: Erratic tach readings

Posted: Tue Jun 07, 2016 5:04 am
by Fastjeff
Like they do in the submarine movies!

Jeff

Re: Erratic tach readings

Posted: Wed Jun 08, 2016 6:52 am
by bill
BigM
A dead blow hammer :roll: is a handy tool :!:
:lol:
bill ;)

Re: Erratic tach readings

Posted: Thu Jun 09, 2016 5:16 am
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