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20 hp 2011 4 stroke mercury, no spark, low compression ☹️

T

Tohatsu

New member
Have a 20 hp 4 stroke 2011 ran 3 trips, fresh oil fuel perfect. 3rd trip engine quit on plane, low oil pressure alarm came on as engine stopped. Checking oil full, motor restarted and ran and quit.
On shore
tested COMPRESSION both low 60's# bad☹️ did not run leak down test.

Tested spark none removed black yellow kill wire from remote

Removed grounded oil pressure switch.

Testing coil can't find service update to test these?

Looking into pulling fly wheel to inspect timming belt, maybe slipped a tooth? Need to verify top cylinder is #1 and at tdc how timming marks should line up?

Seems funny that two problems accured same time but nothing is easy.
Any thoughts really appreciated.
 
Pulled flywheel and the timming marks line up at tdc, so unless the decompression system to make starting drops cylinder pressure down not looking like a good out come ☹️
And still no spark , trying a CDI unit to see if I can accomplish one correction, next step probably drain oil and inspect for internally damage? Metal fragments.
 
Problemo solved, checking the coil, CDI unit, lastly WTF the Exciter they never go bad pulled flywheel again, after I checked timming previously, poking around DAM the wire harness was rubbing thru on flywheel! Right after tie down strap! I'm sure this is a common problem on mercury / Tohatsu motors in the 15-20 hp range ! Can't post pictures too bad
 
Bad gage reading (I suspect). Very small displacement, so if one uses an automotive monster tester...

Jeff
 
I had a 2010 Mercury 20 (so same engine) come in. Customer complaint: ran poorly and died. Starts & idles but no power. I always start with spark & compression check. Great spark, 60# in both cyls. Came here looking for answers why it is so low. Strange. Plugs are both black and the wrong plug so my plan is to put new plugs in, hook up a known good fuel source and try it.
 
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