Testing no spark on a 1991 3 cyl 75 hp Merc

Gary H NC

Fleet Admiral
Joined
Dec 1, 2005
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I don't have a manual for this motor and need to figure out why there is no spark to any cylinders.
I am good on the Johnny Rudes but these Mercs get me confused.
Any tips to test the power pack?
Its on a pontoon that the owner had passed away and i would like to get it running for his grand kids without throwing parts at it.
Any help on where to start testing the electrical would be appreciated..
 

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: Testing no spark on a 1991 3 cyl 75 hp Merc

Pretty hard to test the power pack but you can test everything around it and via process of elimination confirm a bad pack.

The ADI system in the older 70hp is pretty much the same as yours so the troubleshooting info in this recent post will apply:

http://forums.iboats.com/showthread.php?t=331015

Check stator resistance, trigger resistance, coils' resistance, pull the kill wire(s) from the pack, if you find nothing to indicate problems with those components, probably the pack.

If you have access to a DVA meter it'll likely be of great help in a diagnosis. Otherwise resistance checks are pretty reliable.

HTH & let us know what you find.........ed
 

Gary H NC

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Joined
Dec 1, 2005
Messages
8,972
Re: Testing no spark on a 1991 3 cyl 75 hp Merc

Thanks for the reply Ed,
I will be checking it over in the morning and post what i found..
Thanks for the link too...:D
 
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