Why do my ignition coil keep going bad after I replace it

[Nai]

Hi there i have a 87 bayliner capri with a us marine 85hp force outboard. I've been having problems with my ignition coil going out on me I replace it an run for about 30 mins an start it back up an the top coil stop sparkling I replace it 3 times already on the same cylinder. After I replace the coil it will start an runs fine once I take it out it will start an runs normal after I get to my dissertation I shut off the motor then later I go to start it up an the coil is out an i will have to drive it back with 2 cylinder going about no more then 5mph. I can't figure out the problem any help will be great thanks

 

[pnwboat]

It's not very common for the ignition coils to go bad. I would guess that you either have a bad connection on wiring for the CD Module, or a CD Module that is failing after it heats up.

 

[gm280]

:welcome: Nai to iboats. Nice you could join us...

Obviously the only reason any coil opens up is it burns open. And that means too much current flowing through the coil. Is there any ballast resistors missing or anything like that in the top ignition setup? I would swap everything from the top circuit to one of the other cylinders and see how that works out. And I would even change the spark plug as well. If that doesn't fix the top cylinder problem, you need to check what is feed that top coil. That would be the next item to test and/or replace. JMHO

 

[alldodge]

Howdy

Was the coil replaced with new, and did it come with a new plug wire?
Have you replaced the spark plug?
Is there a even air gap between stator and flywheel magnets?

 

[Nai]

Hi you guys thanks for the reply. I did replace the coil with a brand new coil before an took it out 3 times and it went bad an the spark plug has been replaced after 10 runs on the water. I do have new spark plugs into them right now. The first time it went bad I replace it with a used coil that coil last me 1 year in half then it went out on me so I order a new coil not used new an install it an last it me 3 runs on the water and then it went out so I decided to replace it with a used coil an now it only lasted me 1 time didn't even last the whole day I was 5miles out an had to run it on 2 cylinder to get back to the dock.i will be doing what gm280 said an will get back to u guys an thanks for the help I will keep u guys update

 

[sam am I]

Remembering back to my old TV repair days when the 2nd anode, due to a Flyback transformer failure, would do the Tesla thing, corona glow and all.....Arcing like mad until the x-ray circuit kicked in (if it kicked in). Only got bit once over those years, 40KV must have been..............should of stopped then but, noooooooooo

Thinking it's either the stator (exciting coil) and/or the CDI (Switch Box).

Basically, the CDI Ig. uses the induced voltage (magneto if you will) generated from the flywheel's perm magnets passing by the specific exciter coil's in the stator to charge a capacitor (some use an internal oscillator tanking at some resonate LC freq, whining away). that lives in the CDI box (Switch Box)..The "C" (capacitor) in the CDI box is in series the the primary side winding of the ig. coil.

To fire the plug, the charged up cap is discharged (SCR (or FET) grounds the cap via signal from the "other" flywheel stator trigger winding) through the ig. primary coil winding and through the magic of Faraday's Law, the "turns ratio" creates a proportional stepped up voltage on the secondary winding of the ig. coil of say 20KV that arc's at the electrode of the plug.

Say something like 1:100, so if the cap normally charges to say 200VDC on it the secondary of the ig.s coil would have 20,000VDC

If that capacitor becomes over charged somehow by a fault/s in the stator 's (shorting winding's and the like) exciter coil's and/or internal to the CDI (rouge oscillators etc, who knows) and say the cap ends up with 400VDC, then you end up with 40,000VDC and so on and so forth.

At some point, with excessively high voltages, the insulation resistance rating of the rubbers/plastic etc all used to make the ig. components is exceeded, things start to ionize and arc'ing (Tesla coil style) starts happening all over the place...Super high voltages have magically ways of getting out/through stuff

I'd bet if you measure the primary voltage in the Ig. coils, its waaaaaaaaay high. Just a guess though

 

[pnwboat]

Try measuring the resistance of the windings in the coil. That may help determine whether or not the coil is bad. You can also measure the output of the CD Module to determine if it's within specs. Also make sure you're the correct surface gap spark plugs. This version of the Prestolite ignition system requies a boost gap plug. NGK BUHX, or Champion UL18V.