Mercruiser 7.4 L burning out ignition coils

crownline98

Recruit
Joined
Jun 12, 2012
Messages
1
I own a 98 Crownline with a 7.4 L mercruiser. I've had the boat in multiple shops and keep having the same problem. Everytime we take it out on the water it starts up perfect and runs great for about an hour or so. After that, the boat starts sputtering and will die without my control. It will keep restarting and doing the same thing for a little longer then will eventually not even start. Everytime this happens I come home with it and test the coils and they are burnt out. It has had new alternator, ignition module, and multiple other hail mary parts thrown into hoping to fix it. I have exhausted everything I can think of. PLEASE HELP!!!
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,621
Re: Mercruiser 7.4 L burning out ignition coils

Post the serial number of the engine, as that will help with the understanding and diagnosis.

Does the mere replacement of the coil immediately fix the problem? or are other parts being replaced at the same time?
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
Re: Mercruiser 7.4 L burning out ignition coils

Are you sure the coil is failing? voltages and alt check out for overvoltage, replacing it makes it work again but did it fail internally or externally.
check the coil towers on your bad coils for cracking. use a magnifying glass too.if you lose a plug wire that 40,000 volts needs to go someplace, if not thru the wire to a sparkplug, then thru the coil tower to the metal casing of the coil.spits ,sputters and finally quits.
 
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