Hey guys, been a member for a little while now, been doing lots of reading but this is my first post. Im a marine mechanic by trade, but primarily only work on Mercruiser sterndrive go fast stuff; Fountains, Formulas, Cigarettes etc. (500hp, 500efi, 700sci, so on and so on). So my experience with yamaha outboards is limited to water pumps and oil changes for the most part so bear with me. I have a 2003 F115 that belongs to a family member of mine, that Ive been fighting a run issue on all season and its driving me absolutely insane. It runs great at WOT 6000rpm and all other rpm no issue. However at idle, in or out of gear the thing can barley keep itself alive. Coughs, sputters, and stalls frequently. And has a hesitation or stall when you nail the throttle from idle. So far, SP have been done, all filters including VST have been replaced. Lift pump replaced. Injectors sent out, cleaned and flow tested to be within spec. ISC replaced with genuine yamaha. Cylinder drop test shows all cylinders making power. Fuel pressure runs between 35 and 40psi, and will default to 40psi if i take the reference line off the regulator. TPS shows steady increase in resistance through the sweep and 0.732 reference volts at idle. Fuel is good and have run on portable tank with the same issue. The one thing I have noticed is if I unplug the TPS it seems to idle much better. I know some people have had issue with thermostats but the issue seems to be prevalent hot or cold. Used to be a saltwater boat but its in fresh now and nothing appears to be horribly crusty on the engine. Im on the verge of giving up and tossing a match at the thing but Im hoping someone here can help out.
THANK YOU!
THANK YOU!