2004 Mercury 115 EFI four stroke

by Colin BC
(Queensland Australia )

My mercury 115 EFI four stroke develops an engine miss at around 5000 rpm.

The rpm drops approx 200 to 400 rpm. This miss comes and goes.
It appears to be an electrical the way it comes on very abruptly and returns to normal as quickly.
Engine coil. ?

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Jan 03, 2021
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starstarstarstarstar 		2004 Mercury 115 EFI ignition coil problems.
by: Anonymous

I’ve experienced this issue with both coils recently.
A reasonably reliable way of testing the coil/s is to load the engine ie with a high rpm as you’re doing and when the engine starts to miss retard the throttle. If the miss goes away after repeated doing this it’s going to be a coil.
The Mercury 115 is actually a Yamaha power head.
If your unable to purchase the Mercury part you should be able to source a Yamaha part. I was unable to purchase either here in Australia due to COVID and purchased two Mitsubishi lost spark coils with identical resistance in the secondary and primary coils. They work perfectly, cost less than 50 bucks and have been running faultlessly for over six months.

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