Yamaha F115 problem

[coconutkey]

I have a 2004 Yamaha F115 with 150 hours. It's had regular service and was running fine until recently when it began to stall when decelerating to an idle. It would restart, run a little rough then smooth out and be OK. Yesterday when I slowed down to maybe 1500 rpm it began running very rough and missing. Fearing it would stall, I accelerated and it reluctantly picked up speed but was clearly not running quite right. As I began to slow when approaching my dock it just sputtered and died. No restart possible....it cranks fine but does not fire at all. It has the Yamaha digital gages and I saw no low oil or hi temp alarms. Cooling water indicator has a strong stream. So far I've checked the fuel/water separator (clean as a whistle), the fuel filter on the back of the motor (also very clean and no trace of water or sludge). In-line fuel ball is pumped up and not collapsed. Pulled the plugs and appears to be healthy spark. After reading several posts I began to suspect the idle control valve. On a hunch I advanced the throttle in neutral and it started but runs very rough and smokes and as soon as I reduce throttle it will die. I've examined all the wires and connectors and unplugged and re-seated them with no effect. I don't have a fuel pressure tester or a Yamaha code reader. Anybody have any suggestions on what to check next (aside from the obvious and expensive call to the nearest Yamaha dealer)? I also noticed something that may be totally unrelated or not: Recently, after slowing to idle after a high speed run there was a faint high-pitched squeal or whistle coming from the motor which would stop after a few minutes of idle or low speed running. The timing belt is nearly new and appears to be in excellent shape and I saw nothing which might cause it to make any noise.

 

[rodbolt]

Re: Yamaha F115 problem

make sure the dealership you take it to has a master tech.
I suspect that squel was a sticking ISC valve allowing to much air.
sometimes a sticking ISC will overheat the ECU and take that out with it.
hope not.
ecu is about 982 and the ISC is about 380.
its also why I started cleaning them with compustion chamber cleaner occasionally.
have the tech try the stationary test for the ISC and fuel pump.
if the screen shows the engine is running or in gear stand by.
to find a dealership in your area that emloys a master tech use the yamaha marine dealer locator function.
type in your zip code and expand the search as nessasary.

 

[coconutkey]

Re: Yamaha F115 problem

Thanks, Rodbolt. I appreciate all the insights you provided. Fortunately there is a local marina (Deep Creek Marina) where the owner is also the Yamaha master tech and I'll be taking the boat in for him to check out tomorrow morning. I'll be sure to post the outcome for the sake of education if nothing else. I really like this motor so I want to learn as much as I can about its quirks and potential problem areas.

 

[coconutkey]

And the problem was......

And the problem was......

Rodbolt: For the sake of education, the problem turned out to be a bad throttle position sensor. The tech found it fairly quickly but had to wait for a new one to come in as this part does not fail very often and they didn't stock it. Tech said this is only the second one they've replaced in 7 years. Interestingly, the electronics did not fail.... the unit had been physically damaged prior to my ownership of the boat. The tech found a code for the same problem had been set at 108 hours (I'm now at 151) and figures someone tried to adjust the position of the sensor improperly to compensate for an idle speed issue or something like that. Anyway, when he went to remove it he found a hairline crack which just fell apart when he took out the fastening screws. After getting it back running with a set of new plugs, he checked for any other codes and found everything to be working properly. I guess these are just the things you run into with a used boat...... we'll never know how somebody managed to damage it, but at least its fixed now. This does reinforce the value of some sort of code reader as the actual repair was quite simple and I could easily have gotten the part and done it myself for a quarter of the total cost if I had been able to tell what was wrong. Guess that's why techs command such a premium price. Hopefully it's not a problem that I will ever have again.