2000 Yamaha 250hp OX66 shuts down

[agropic]

Hi Everyone,

2000 Yahama SX 250hp OX66, 3 blade prop 15-1/4"X15"-M.
Boat: 1989 Mako 231 with A&J bracket.

Motor runs fine for a while (15-25mins) at all speeds and RPMs, soon as it gets warmer and hits the 4000rpm or over, shuts down, like if I turn the key off!!

Motor cranks right away if I cycle off-on the key!

This is what I checked and replaced so far:

O2 sensor brand new and clean.
VST filter clean, preasure regulator screen clean.
New VST gasket.
Inline fuel check valve gutted (I was good, but removed just in case).
Injectors clean (fuel injector man).
Fuel preasure on rail @ 40psi.
3 new low preasure pumps and gaskets.
TPS voltage check, 0.50v fully closed, 3.8v at WOT.
Compression 110 all 6.
New spark plugs.
Spark gap good.
Gas and tank are brand new, all filters are new, and new yamaha primer bulb as well.

Motors idles fine, minimun smoke.

At this point im clueless!! Just order a winky blinky harness from SIM to check on the other sensor...

Any suggestions??

Thanks,

Eladio

 

[tommarvin]

Does your motor have a computer on it, to plug in a cable to your laptop for trouble shooting, like a check engine light on a car ? If not , I would guess a sensor, vacuum leak, or air lock in fuel line, or a safety shutoff, electrical problem, I would take the cowling off and and look at every little thing.

 

[N1NE1]

My engine used to go into limp mode due to a bad poppit valve which caused overheating.Is the motor getting too hot?

 

[yamatech43]

Ok, one he doesn't have the software so what good would a laptop do? Two limp mode and shutting down the engine are two different things...now, if you are still checking to see if you actually get an answer....one thing stands out in my mind on this when I read your symptoms and it is that it will run up at high rpm and all for 20 minutes or so.....sounds like you may have high vac developing, could be a plugged vent on gas tank, too small(or too long) a gas line, too small a filter or separator, etc.....I would hook up a cheap vac gauge to motor with cowling off and have someone watch it...at twenty minutes i think you'll start seeing the vac go above 4 and a half inches....maybe

 

[yamatech43]

oh, should say this....when the motor sees five inches vacuum it will shut down, but will usually lose all power, then cut in....then cut out...but if it's the tank itself, due to it's volume of vac....it may shut down completely.