2000 250hp OX66 shuts down at high RPMs

[Capt Picon]

Hi Everyone,

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

Motor runs fine for a while (15-25mins) at all speeds and RPMs (wot @ 5500-5700), soon as it gets warmer and it hits 4000rpm or over, shuts down, like if I turn the key off!!

After the shut down, motor starts right away, when cycle the key off-on !

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 at idle.
3 new low preasure pumps and gaskets.
TPS voltage check, 0.50v fully closed
Compression 110 all 6.
High-Pressure Fuel Pump Resistor: 0.70 ohms.
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.

Still need to check pressure on rail soon after shut down and HP pump amp draw.

Just order a winky blinky harness from SIM to check on the other sensors, should be in by the end of the week (12/24/2015)...

Any other suggestions??

Thanks,

Eladio

[DennisG01]

Is it overheating? I don't know the answer, just wondering outloud - will the computer shut down the engine for an overheat, or just reduce power? I would suspect a buzzer to go off, but possibly the buzzer in not working?

[99yam40]

Monitoring rail pressure and HP pump voltage and amps should tell if it is the problem.
It is not designed to shut down unless you turn off the key.
So you are loosing fuel due to loss of voltage to pump, pump locking up,no fuel in VST for it to pump, or no spark to plugs causing shut down

[Capt Picon]

Buzzer works fine, as far as I know no overheating.

Thanks for the reply!

Is it overheating? I don't know the answer, just wondering outloud - will the computer shut down the engine for an overheat, or just reduce power? I would suspect a buzzer to go off, but possibly the buzzer in not working?

[Capt Picon]

Monitoring rail pressure and HP pump voltage and amps should tell if it is the problem.
It is not designed to shut down unless you turn off the key.
So you are loosing fuel due to loss of voltage to pump, pump locking up,no fuel in VST for it to pump, or no spark to plugs causing shut down

That's my next task...will be done tomorrow. Fuel pump amp when hit the key on is 4.65 amps. Didnt measure voltage !!

Will report results tomorrow.

Thanks!

[bajakeith]

oxy's

I love those motor's, btw..... U might want to just sub out the fuel line to a good known portable fuel cell and test run

[Capt Picon]

I love those motor's, btw..... U might want to just sub out the fuel line to a good known portable fuel cell and test run

Gas tank is brand new, new primer bulb, new gas lines, and new racor filter. And yes, when they are running...they are really good motors.

thanks for the input.

[rodbolt17]

monitor fuel rail pressure at the failure RPM and load.

[Capt Picon]

monitor fuel rail pressure at the failure RPM and load.

Will do tomorrow. I'll report back the findings.

thanks!

[Capt Picon]

monitor fuel rail pressure at the failure RPM and load.

Just came back from test ride:

Fuel pressure at the rail when shut down: 0 psi !!! If I cycle the key OFF-ON goes back to @ 38-40 PSI immediatly.

Fuel pump amp draw when I turn the key is: 4.65 amps.

Hook up the test harness (winky blinky)code 1 Normal operation.

Whats next? Bad pump? bad relay? bad resistor??

any suggestions ?

What's next

[99yam40]

Monitoring rail pressure and HP pump voltage and amps should tell if it is the problem.
It is not designed to shut down unless you turn off the key.
So you are loosing fuel due to loss of voltage to pump, pump locking up,no fuel in VST for it to pump, or no spark to plugs causing shut down

if pressure drops to 0 you need to find out why
does it loose voltage?
do the amps go up do to locked up pump
do they just go down but still have some current indicating pump is running but not pumping anything?

[rodbolt17]

you can fugget about da resistor.
it aint bad.
my guess is your running out of fuel in the pump due to a clogged VST filter.

that motor needs a minimum of 25 gallons an hour past the injectors at or near WOT. if it cant get it it sometimes shuts down violently.

[Capt Picon]

you can fugget about da resistor.
it aint bad.
my guess is your running out of fuel in the pump due to a clogged VST filter.

that motor needs a minimum of 25 gallons an hour past the injectors at or near WOT. if it cant get it it sometimes shuts down violently.

Got you. I will re-check the VST and get me a new VST filter. My lowrance gas flow meter (mounted in between the primer bulb and fuel/water separator filter) does not show that amount of fuel being draw. Its showing @ 7-8 gph max at wot.

thanks

[boscoe99]

Got you. I will re-check the VST and get me a new VST filter. My lowrance gas flow meter (mounted in between the primer bulb and fuel/water separator filter) does not show that amount of fuel being draw. Its showing @ 7-8 gph max at wot.

thanks

Does the gauge work correctly?

I can't imagine any 250 HP engine that can run on 8 gallons per hour. Or anywhere near that amount.

Ruff rule of thumb is that fuel needed will be at or near 10% of the HP output. 250 HP at WOT would equate to 25 gallons per hour. The OX66 is known as being a thirsty model by the way.

Something is not adding up.

[rodbolt17]

over the years I have personally ran enough 250 OX66 motors to tell you at or near WOT it consumes 25-29 GPH. it how they work. 2 or 4 stroke.
last summer I took a boat out with triple 350's, at 5400 the flow was 94 GPH.