My F80 won't quit!

[MercuryBay]

Hi boaties.

I have a technical issue with my Yamaha 80 four-stroke, all other avenues have come to a dead end so hoping your collective wisdom may throw up some ideas!

My motor is an F80A model, unsure of vintage but likely 2002-2005 with around 600 hours on the clock. A while ago it developed a habit of not shutting off. It literally developed a life of its own – key off, dead-man’s switch pulled, battery isolation off, motor still ran! (Bit of a novelty after years of owning a Suzi DT85 that wouldn’t start, now my new motor won’t stop)! The problem is sporadic and unpredictable; maybe five out of ten times it won’t happen.

Predictably, the yard replaced the ignition/key switch/barrel, but this did not resolve things. Weirdly, I have found a way to stop the motor – turn the key to off as normal, then just touch the motor trim up or down and it stops. That, for somebody electrically minded, must be a major clue!

Not over yet though – along side this, when running at all speeds the motor has weird ‘moments’. The information on the twin Yamaha displays goes crazy and flashes, and the motor drops a thousand RPMs and runs roughly, almost as if it has dropped a cylinder. This is sporadic, totally unpredictable and has never resulted in a breakdown – just a bit of embarrassment as people think I am driving like a ****. I am convinced that these two problems are closely linked, and to state what must be obvious, that this is an electrical issue. It has occured to me - could this be the motor going into 'self-protection mode' - as if it was low on oil or overheating?

What have I done so far? I have checked all visible connections and earths; all that I can see are in good condition and tight. With the motor over-running and ignition off I have felt my way around much of the cabling, hoping to expose a loose/intermittent connection or broken wire. I have learned that the black/white wires are related to the ignition stop circuit, so focusing on this.

Any ideas, anyone?

[99yam40]

sounds like a bad connection in wiring .
might try disconnecting , inspecting , and cleaning every connection you can in the harnesses and battery cables.

I would try to locate the kill wire at the ECU and try grounding that at the ECU itself when the motor will not shut off

[boscoe99]

Take one problem at a time. Starting with the motor not stopping.

With the motor running, disconnect the ten pin connector at the front of the motor. On the engine harness side, find and jumper the white wire terminal to the black wire terminal.

The motor should stop. If it does, fix the problem in the ten pin harness or in the boat. The problem of the white wire not being grounded when the key is turned off or the kill switch pulled.

If the motor does not stop, come back here for further advice.

It would be nice if we had more of the story. What kind of control box are you using?

[rejesterd]

I would test the main relay to see if it's stuck. You can try tapping on it with a screwdriver after turning the key to OFF, or remove it and test it electronically.

[MercuryBay]

Thanks for the info guys, really appreciated. Got caught up with other things so was slow to tackle this while not having the boat on the water. I worked my way around the whole wiring loom, checking as much as possible end to end focusing on connections etc., checking for tightness and to ensure they are clean. Weirdly, the last time I had run the motor and experienced the not shutting down problem, a gentle tap on the ECU stopped it instantly. Since doing all of the above, I ran the bloody thing for ages and stopped/started over thirty times, couldn't get it to fail once. This, I guess, is good news, though of course it niggles me that I never found anything wrong. I also won't know if this is/was related to other problem until I can get her on the water, hopefully this weekend. But meantime, thank you for your advice.