2003 f115

[hfhboats]

I have read a number of threads trying to find so answers to my issue. I have a 2003 F115. It starts easy and runs great. However, when you drop from a high to moderate RPM back toward neutral the boat stalls. This happens in both Forward and Reverse. The boat starts right backup without issue. It was suggest in other threads the neutral position switch may be the issue. I have changed the switch and still have the same issue. Can anyone shed some light on this for me.

[greasyshaft]

Does it only happen when you slow down rapidly? try easing off the throttle very slowly.
Could be a bad ISC valve, you should hear it resetting at key off (ticking noise better heard with cowling off) but could be different for your country.

If you have YDS that would tell you if you had a bad neutral switch (switch should be off when in gear)
Best to take it to a good dealer and have them diagnose the problem.

[hfhboats]

if I let off the throttle slowly it comes down fine and does not shutoff in both reverse and forward. It only happens in rapid deceleration.

[rodbolt17]

3 things to watch at rapid deacceleration.
rail pressure,to much and its way rich.
TPS Voltage.
and the ISC commands.
remember the ECU commands the ISC but doesn't know if it followed the command.
kinda like kids and dogs.

[hfhboats]

RodBolt thanks for the direction. I guess it is time to buy some diagnostics. i am a pretty good mechanic but new to Yamaha. I seven of them now. Time to bite the bullet.

[boscoe99]

3 things to watch at rapid deacceleration.
rail pressure,to much and its way rich.
TPS Voltage.
and the ISC commands.
remember the ECU commands the ISC but doesn't know if it followed the command.
kinda like kids and dogs.

Why would there be too much rail pressure?

The regulator only increases fuel pressure for acceleration I believe that I heard you say. If an acceleration event has not happened in many minutes time and the throttle is merely pulled back to decelerate the motor, then how is the fuel pressure coming into the equation?

[hfhboats]

A stupid question for those of you who know. Where is th ISC valve located. I have tried to locate it on the parts breakdown.

[boscoe99]

A stupid question for those of you who know. Where is th ISC valve located. I have tried to locate it on the parts breakdown.

Item 8 in this illustration

2006 and Later F115TXR Yamaha Outboard INTAKE 2 Diagram and Parts

[rodbolt17]

cause fuel return paths can clog and spike rail pressue and regulators can get sticky.
next question grasshopper.

this motor uses a stupidly simple speed density setup just like GM,yamaha,OMC,Volvo and many other stupidly simple EFI setups.
whats funny is the MOST critical thing is RAIL pressure yet its NOT monitored at all.
that stupid ECU ASSUMES its correct.
any one that's ever watched the Odd Couple KNOWS what ASSUMES means.