90hp Johnson 2005

Hello everyone I have a 90hp out board Johnson an it runs great for about 3 min maby less and then it just starts cutting out. The guardian kicks in I have to turn off the boat an then it will work again for a small amount of time. Cant figure it out can any one help!!!!! I have replaced the impeller an the thermostats it was getting hot an I would get an alarm form that. This is when it all started after that it has gone down hill. An when I put in gear some times it dies i have to punch it an then ease back quickly because I'm in a no wake zone and then normally its ok. I am thinking it might be the coil or the temp switch but I don't always get a hot alarm, how would some one go about testing the coil. I know today when I took it out it wouldn't start once I was on the lake an got that alarm an truned it off. went to turn it back on an I had to disco the battery an then it worked ok for a bit then started to do the same thing. An some times seems to idle a bit rough so I'm leaning towards the coil but don't know to test to see witch one is bad. Any advise would be greatly appreciated. Thanks

Have you tested the spark on each cylinder? That's the first thing I'd do...if you don't have a spark tester, Mr. Joe Reeves has discribed how to make one on this forum. Let us know what you find.