What are the symptoms of a bad coil?

[stelladallas]

How will my 70hp Johnson run if I have one bad coil?

 

[jbjennings]

Re: What are the symptoms of a bad coil?

A bad coil can go in and out and cause power surges when you get spark on the dead cylinder. It can just lack power totally because one cylinder is dead from no spark. OR, it can run fine, then when the motor warms up and thermal expansion causes you coil to go out, then lose power.
I would think that the simple way to find out would be to check spark, then switch coils and see if the spark failure followed the coil. If you have intermittent spark because the coil goes in and out, it's harder to diagnose. Lots of times, you can pull the plugs and see which one is dirty/oily to find out which one isn't getting good spark.
Good luck,
JBJ

 

[francistran7]

Re: What are the symptoms of a bad coil?

I think i have a problem with my coils on my 175hp mercury. it starts first try cold but once it gets warm it wont start for anything. i know its been a long time since this thread has been posted on but if you could, could you give me a update on if you got it to work and what you did? thanks.d

 

[archcycle]

Re: What are the symptoms of a bad coil?

I think i have a problem with my coils on my 175hp mercury. it starts first try cold but once it gets warm it wont start for anything. i know its been a long time since this thread has been posted on but if you could, could you give me a update on if you got it to work and what you did? thanks.d

Check out the Mercury section of iBoats:
http://forums.iboats.com/forumdisplay.php?f=25

You can check the coils by putting a timing light on the plug wires while running the engine in the same situation you normally experience the problem. Good ones fire steadily and bad ones miss or don't fire at all.

 

[kenmyfam]

Re: What are the symptoms of a bad coil?

Very old thread to go at again. Suggest you start a new thread stating the issue. Mod's will likely close this one.