Yamaha 225 OX66 shuts down

[BOAT DOCTOR]

i have a yamaha 225 OX66 the motor willrun50 to 75 yards and then shuts down when i mean shuts down as if you would have turn the key off but only will shut down between 3200 rpms and up anything under motor run great all the way up to the point where it shuts down and soon as it shuts down it will restart and run 50 yards and kill again went through whole fuel sys. clean and change fuel filters all except high pressure filter but fuel was never bad had trash or water.compression good.also used a another good control box eliminating main harness tried new 6 gallon gas by bypassing boat fuel tank still shut down also clean the oxygen sensor samething shuts down running out of ideas any suggestions

 

[99yam40]

Re: Yamaha 225 OX66 shuts down

An inductive timing light should show if the spark is going away .
If it is not spark lose then chase fuel issue. Have you measured fuel pressure as the problem appears?
Does that motor have a low speed and a high speed pulsar coil?
I am not sure how that works but I have heard of motors having them. Just a thought

 

[BOAT DOCTOR]

Re: Yamaha 225 OX66 shuts down

fuel pressure 38 psi when turn key on and while running fuel pressure stays between 38 to 40 psi.i think that is within spec.check all grounds they are tight and clean.check continuity on main harness all checks out.

 

[99yam40]

Re: Yamaha 225 OX66 shuts down

Still does not say if the fuel pressure drops when problem occurs or if spark goes away

 

[rodbolt]

Re: Yamaha 225 OX66 shuts down

your describing a classic fuel starvation on an EFI motor.
drop rail pressure below about 25 PSI with the throttle open and it shuts down just about like you switched the key off.
really dont care what the rail pressure is at idle,what does it do at the problem RPM under a load.
that engine does not use a high and low speed charge coil, its one charge coil for each cyl bank.
it does use a resistor for high and low speed VST pump operation and if the pump attempts to draw more than about 6 amps it will shut the ECU down.
it also uses 6 pulser coils sharing a common ground.
lose the pulser coil assy ground and it shuts all 6 cylinders down.
ign issues are incredibly rare,fuel system issues are common with todays fuels.
when was the last time the lift pumps were inspected and the VST filter cleaned? has to be done as periodic maint just like the manual says.

 

[BOAT DOCTOR]

Re: Yamaha 225 OX66 shuts down

fix it it was high pressure fuel pump.pump was $900 dollars yamaha must proud of there parts thats a crazy price for a fuel pump.

 

[rodbolt]

Re: Yamaha 225 OX66 shuts down

told ya, your describing a classic loss of rail pressure issue.
sorry it was the pump. pump failures are rare to, usually it will age and draw excessive current and the ECU cant supply the ground anymore so it shuts down.
pump amp draw above 1800 RPM should be less than about 6 amps. much more and the ecu ground goes away.