ox66 shut off

[Blue197320]

hi this is my first post but i will say that i have done research and used the search fuction. my motor is an 01 0x66 225. it has 3 new oem lp pumps, the injectors were just cleaned ultrasonically. has a new tp sensor installed. no water in fuel. the high pressure pump did seize up but i was able to free it up soaking it in fuel injector cleaner.

the boat will start and idle perfect all day. when it gets on plane around 3.5k to 4k rpm it will cruise there for a minute or two then just shut off like the lanyard was pulled. it will not build fuel pressure again unless you cycle the key off and back on. the mechanic and i water tested the boat with a fuel pressure gauge and test light. the fuel pressure is at 0 when the motor shuts off and he says ground is lost after the pressure falls. he says hes never seen this before. he determined high pressure pump based on the way it just looses pressure and given that it had seized before. i put a new oem yamaha pump and new vst screen in and water test the boat today. same exact thing happening. plane out to 4k and after 2 minutes shut off again. i have the factory manual and tested the inline high pressure pump resistor which is in line with the blue (negative) pump wire. spec is .53 to .57 ohm. it varies on my dvom from .5 up to .7 ohms. i was not able to check the resistance while the boat was running. i need this boat fixed asap, fishing tournament coming up and paid entry fee already. please help!!

[99yam40]

ECU controls fuel pump by switching the ground.
If ECU does not see motor running it shuts off pump,
I am not sure what it uses to monitor the motor running, manual should give that info

[Blue197320]

i have been looking over the wire diagram all day and i cant find where it goes to ecu to get ground. the blue wire on the negative side of the pump goes through the resistor and then looks like into the charge coil. the red/yellow wire appears to have alot of splices branching off to each injector and going to the main relay eventually that color wire goes into the ecu connector.

[rodbolt17]

above 1200 RPM the resistor is out of the circuit, the ECU takes the blue wire to ground directly.
carefully test the pulsar coil inputs to the ECU.
carefully test the ECU grounds.

[Blue197320]

a hydraulic steering hose blew on the water test yesterday. when i get that fixed i will be updating here with the findings. thanks for the replies

[Blue197320]

ok some news, the steering is fixed. the boat is still sad. fuel delivery has been eliminated from tank to vst. ecu has been eliminated. swapped in a different ecu with same result. by-passed fuel pump ecu ground and have same result. by passed power and have same result. eliminated a harness problem. now the mechanic is leaning toward ignition issue.

[Snow Bird]

I have triple ox66 250hp motors on my boat and pretty much experiencing the same problem as you with one of the motors.When motor runs under 4300 rpm motor runs fine, over that say 4500 and up motor runs 3-5 minutes and cuts out as if you turned off the key switch. Stop the boat it starts back up immediatly and goes again fine but just once you dont go over 4300rpm. Also cuts out if you idle motor around for say 10 minutes bringing boat into dock. Notice when engine running 4300 rpm water pressure gauge is higher than other motor could there be a blockage in the water passages causing motor to cut out at high speeds water or oil alarms never go off and are working fine. So i am watching this post for answers i have checked what you have checked already and switched ECU and no change also switched fuel pump relay and no change.

[Blue197320]

the boat is back at the shop, he is starting to think its a stator. we ran it last night at 3300 to 3500 rpm and it wont duplicate the problem. get it up to 39-4000 and it will shut down. he is thinking that with the load from the higher rpm the stator is getting hot.

[Lake O Hunter]

ox66 225 similar problem

I am not trying to highjack the thread, but I am having similar problems....my '03 225hp ox66 will run like a dream one trip out; next trip is soon as i throttle up to 2500/3000 rpms it dies. I can usually idle home with it only dieing once or twice, but its a long slow ride. I have:
-checked/cleaned vst filter - minor grime, but good now.
-replaced plugs
-replaced mechanical fuel pumps
-replaced battery cables and battery switch (not the yamaha engine to battery switch) just the cables from switch to battery
-replaced internal fuel filter
-replaced fuel/water separator

Each time it seemed to cure the problem for about two trips...mine sounds more and more like the bad ground referenced above....

[rodbolt17]

all the above are easily tested, check rail pressure at shutdown,monitor stator output at shutdown,monitor main relay voltage at shutdown.
measure pump amperage draw at shut down.
no spec on the draw but typically anything over 6 amps will cause the ecu ground path for the pump to fail.
loss of rail pressure will cause a shutdown similar to ign off.

[Lake O Hunter]

Thanks I will try to monitor all these things next weekend when I work on it; it sounds like it could be as simple as a bad ground?

[Lake O Hunter]

My problem rears its head after months of not being an issue; problem doesn't occur when boat is on trailer and running on rabbit ears....

So the ox66 is back to shutting off as soon as I throttle up to get on plane; roughly 2200rpms. Problem does not occur when I throttle up the engine while the boat is sitting on the trailer hooked to a hose?