96 150 Mercury efi some pistons not moving

wells8696

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Mar 13, 2021
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Hey all hoping someone has a little info on the problem I am having. A few years ago I was running about 30mph down the lake when my 96 150 Mercury EFI slowly started losing power with no alarms I quickly killed the motor and heard a light “tink” noise in the top of the motor after the motor had completely quit running. I tried to restart the motor and it acted like the motor was locked up. Long story short I brought the boat home and parked it for about a year. Frustrated I finally took the motor cover off pulled all the plugs out. The fly wheel turns but only four pistons are moving in and out. All six of the cylinder walls look brand new and smooth. The very top right and the middle left pistons are not moving but the rest are when I turn the fly wheel. My question is does anyone know since the motor is turning freely and the two pistons are not moving what could this possibly be could it just be the connecting rods? Or does anyone else have any ideas I am thinking about tearing into the motor and was trying to get a feel for what any of you think it could be. Is it possible that the oil injection went out and those two cylinders overheated and swelled up causing the motor to temporary lock up until cooled down? I didn’t think it made any sense why it sounded locked up at the lake but then after sitting a year it turns freely???? also when this happened it made no noise at all while the motor was running . Any help would be unbelievably appreciated!!!!!
 

Dukedog

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Oct 6, 2009
Messages
3,420
sounds like tha crank broke.. maybe rods but usually if rods break it tears up a lot more stuff and will only turn a little one and/or both ways.. not to common but does happen...
 

wells8696

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Mar 13, 2021
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sounds like tha crank broke.. maybe rods but usually if rods break it tears up a lot more stuff and will only turn a little one and/or both ways.. not to common but does happen...
Thank you so much for the response would it do all that without a sound at all? Like I said it was quiet when it happened all I heard was what sounded like a rod or bolt falling after the motor was completely off not sure?.....
 

wells8696

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Mar 13, 2021
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Thank you so much for the response would it do all that without a sound at all? Like I said it was quiet when it happened all I heard was what sounded like a rod or bolt falling after the motor was completely off not sure?.....
And also the flywheel turns fine as much as I want it too with no noise at all and really smooth
 

Dukedog

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Oct 6, 2009
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3,420
yes it could.. only crank i had break several years ago it broke so clean tha motor would try ta run on 4 cylinders.. not to good but would still try ta run....
 

wells8696

Recruit
Joined
Mar 13, 2021
Messages
5
yes it could.. only crank i had break several years ago it broke so clean tha motor would try ta run on 4 cylinders.. not to good but would still try ta run....
I appreciate you letting me know that I’ve never been into one before so didn’t know what I was up against.....
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,904
It being #1 and #4 not moving I would look at ignition system reeeealy good
 
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