[scottpellegrin]

Over the last few weeks my engine would misfire on occasion when at wide open throttle. Some times just a little blip, other times I would have to go to 3/4 throttle to get it to stop misfiring. Just last night I ran 3 miles across lake wissota with no trouble at all. I stopped and fished for about 45 min then started the engine again and was going to head up just a little farther. As soon as the boat got on plane the engine killed as if I had turned the key off, no spit or sputter at all. I checked for spark when I was on the water and there was none. Tonight when I got home from work I thought I would put the muffs on it and try to start it. Soon as I turned the key it fired and ran perfect. I let it run for about 5 minutes and then shut it off and wrote this message. Where do I begin with this thing, or what do you think the culprit might be? Just a note I worked on helicopters for 5 years so don’t be afraid to put me to work with troubleshooting this thing. Any help would be greatly appreciated.

[Chris1956]

First I would eliminate the SLOW system as a problem. Start and warm the motor. Run the motor at 3/4 throttle and feel the heads. If they are not overheating, you may have a bad temperature sensor. Now disconnect the port temperature sensor, and try that WOT run. If the miss disappears, you have found the culprit.(bad temp sensor)

When you lost spark, did you lose it on both sides of the motor? The shift assist module kills spark to one side. You may need to disconnect that and see if that is the culprit.

Other than those two possibilities, make sure your getting enough fuel flow.