2003 Yamaha F90 dies when approaching WOT

GGuerry

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Mar 10, 2016
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2003 Yamaha F90 runs fine on the trailer with water hose, can reach WOT, no problem. Also will do WOT on the trailer in the water at the landing in gear and run for hours... however when leaving the dock, the engine consistently dies when speed goes above slow idle. Engine dies completely, no stutter, no rough running, it just dies as if the key was turned off. This happens every time at just the same level of throttle. The engine will not restart before sitting for 15 minutes or more, it will then restart and I can idle back to the dock. I have rebuilt the carbs, installed new water pump, thermostat and temp. sensor. None of these repairs have fixed the problem. Any suggestions would be greatly appreciated and I am committed to sharing final results here. Thank you
 

lmuss53

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Sep 9, 2008
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Can be lots of stuff. I would get a 6 gallon tank and a new hose and try to run it on that. I had a similar issue on a Starcraft once and found a kinked fuel hose between the tank outlet and the motor. Get someone to pump the ball up hard and keep pumping while you try it. If it runs OK then look to the fuel pump. Running on a hose or even in the water at the ramp doesn't use any where near the fuel that trying to get going in the water requires, The 15 minute thing also suggests a blocked fuel tank vent or possible electrical issues that come out once the engine gets warm. Try pumping the ball, and then a new tank and hose, easy to do and cheap.
 

99yam40

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Sep 7, 2008
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you need to test things when it happens
is there spark to all or some of the plugs?
what about fuel pressure.

Does your alarm system work?
how did you test it to make sure?
 

robert graham

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Are you running the motor in neutral on the water muffs at 6000 RPM's?.... Just curious here...
 

GGuerry

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No, i wouldn’t over rev the motor on the water muffs, I just wanted to point out that the motor would rev up to higher rpms without shutting down as it does on the water. And no, I don’t think the alarm system is working. One odd, possible coincidence is that the first time the shutdown occurred, I had just demonstrated to my grandson how the emergency shut-off lanyard worked. I’m beginning to think this may be a computer issue.
 
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99yam40

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well, 1st thing I would do, would be to fix the alarm system.
it might help in the troubleshooting and it is a system that should be working always.

That being said, have you thought about checking to see if the kill wire is damaged and grounding when moving the controls?
 

GGuerry

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Mar 10, 2016
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Making some progress, I have eliminated the cdi and rectifier: Swapped out the cdi, no improvement. Tested the rectifier, checks out OK. Same issue, runs fine at low rpm, and higher rpm at the dock, in and out of gear. Consistently dies when going over 2000 rpm while under way. Yesterday, I borrowed a friend?s wiring harness and ignition key setup, and amazingly, boat now will operate properly. Today I will try to determine if it is the wiring harness or ignition key by switching them out individually.
 

tommarvin

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Nov 22, 2015
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When old ignition parts get old they won't hot start until they cool down? About 10-15 min.
 

GGuerry

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Mar 10, 2016
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Problem Solved! The culprit is the wire harness extension which goes from just outside of the engine to the console where it connects to the ignition key assembly. I don?t know why it went bad. I may be able to tell when I pull the old one out.
 

GGuerry

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Mar 10, 2016
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No Title

Squirrels!
No kidding, I removed the bad wire harness and discovered that a squirrel had bitten into the cable, doing serious damage in an under deck location that was not visible but apparently very cozy for the squirrels. I have no way to tell just what was happening with the engine, just know that the new cable fixed the problem and I will try to keep the critters out of the boat in the future. Thanks for the helpful suggestions.
 

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tommarvin

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Nov 22, 2015
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999
Wow, that happened to a friends car, but I've never heard of it happening to a boat.
Thanks' for sharing that with us.
 
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