1989 90hp Merc 3 cylinder No spark on top cylinder when cold

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fossel

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My 1989 90hp Merc, 3 cylinder, won't spark on the top cylinder until engine warms up. After the cylinder kicks in the engine runs fine. I have moved coils around and the lack of spark stays with the top cylinder. I am waiting for a flywheel puller to be delivered so I can access the stator and trigger. Are the switch boxes a common issue with these engines? I don't have the DVM tester for the trigger, I'm trying to solve this myself before I take to a mechanic. Any ideas of where to concentrate my efforts?
 
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oldman570

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Re: 1989 90hp Merc 3 cylinder No spark on top cylinder when cold

I would guess the switchbox is the problem as the plug starts firing after a warm up time. The boxes on those motors are noted for going bad. A manual will tell how to test the trigger and other componets of the ing. system and are needed if you plan on working on it. Sort of a must have and not that expensive.
Oldman570;)
 
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CharlieB

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Apr 10, 2007
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Re: 1989 90hp Merc 3 cylinder No spark on top cylinder when cold

It is NOT the stator.

A trigger wire can be broken and as the throttle is moved the ends abut and start firing.

Test spark on all cyls, switch trigger leads on the switchbox to see if the 'no spark' changes, if yes it is the trigger, if no it is the switchbox.
 
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1nebel0

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Nov 28, 2005
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Re: 1989 90hp Merc 3 cylinder No spark on top cylinder when cold

Almost always going to be the switchbox...trigger fail rarely but as Charlie says above, testing is alway best rather than throwing parts at it..
 
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fossel

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Re: 1989 90hp Merc 3 cylinder No spark on top cylinder when cold

Thanks for the help men. I have narrowed it down to the switchboard. The leads coming from the trigger all have power going into the switchboard. The leads leaving the switchboard going to the coils 2 out of the 3 showed signs of life, the one to the top cylinder was dead until the engine warmed up and the top cylinder kicked in. Then there was power leaving the switchboard to all three coils. Also the switchboard was now warm to the touch. I've ordered a new switchboard, when I receive it I'll know for sure. I'm pretty confident the switchboard is the problem. Again thanks for the replies. Jim
 
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fossel

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Re: 1989 90hp Merc 3 cylinder No spark on top cylinder when cold

Damn autocorrect. Replaced switchbox with switchboard
 
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