2001 ox 66 250 hp twins acting up help

[Whalure]

Yesterday coming home had run boat over 60 miles with no problem, had been crusing 3800 rpms at 27kt on a 27 whaler, when my temp alarm goes off on port motor. Temp indicator was flashing on tach, along with steady alarm.

I killed port motor, and kept putting trying to figure out what was going on. It was peeing great and not any hotter than starboard motor. As i was checking the starboard motor started cutting out rpms, and surging.

I recranked port motor and throttled up, alarm stopped and boat planed. Port motor was running great again, 4400 while other motor was only getting 2800 to 3100. I had to keep pulling trottle back and forth and it gradually started building up more rpms.

Did this for a few miles, dropped dad off at his dock, and when I pulled off both motors throttled up and ran great again, crusied at 4400 rpms for probably 15 miles.

They did the same thing again, I pulled to marina and stopped for a few minutes. Pulled out hit gas and they ran great again rest of way home for 10 miles.

What could be my problem that would cause both motors to act funny at the same time and then start running so good again?

Thanks in advance

 

[MikDee]

Re: 2001 ox 66 250 hp twins acting up help

UFO's!

Actually a lean condition would probably cause overheating, & stumbling, temporarily taking out both motors.

 

[ghind]

Re: 2001 ox 66 250 hp twins acting up help

Lean fuel conditions are about the only thing that makes these motors go boom.

Get it fixed, do not use it like this.

There is lots of info on here about these motors, do a search for ox66.

If you run into this again, slowly drive straight back or you will be replacing powerheads on one or both motors.

 

[Whalure]

Re: 2001 ox 66 250 hp twins acting up help

Whats the best way to check for lean condition? Pull plugs? I read several threads on ox66, most talk about cleaning o2 sensor, vst filters and low pressure fuel pumps, which I plan on having mechaninc clean and replace.

Thanks

 

[JUSTINTIME]

Re: 2001 ox 66 250 hp twins acting up help

pull the plugs and look at them

 

[Whalure]

Re: 2001 ox 66 250 hp twins acting up help

I posted this thread in August, and after taking boat to shop, and replacing low pressure pumps, cleaning 02 sensors, and vst filters boat ran great for proably 60 hours. Had it out 20 miles offshore last week and exact same thing happened as last time.

This time noticed that buzzer alarm did not work on starbd tach. Even though rest of tach worked fine. Took it to mechanic, he ran diagnostic check on both motors and compression check on both motors and said compression was about same on all 12 clyinders around 110 to 115.

Also said it was actually the starbd motor overheating. Motors are on bracket and when it happened both times I had them trimmed up and was running around 4800 rpms. He is replacing starbd water pump, as port pump was done in August, changing plugs as he said they were pretty black, doing a decarbon on the motors, and cleaning o2 sensor again, also replacing buzzer.

I have babied these motors and he told me to run them hard the last few miles of every trip to burn carbon off.

My question does this sound like it will be the correct fix? Also what should compression be? My guess they will go up some after the decarb. Motors have 702 hours on them.

 

[rodbolt]

Re: 2001 ox 66 250 hp twins acting up help

my guess is you only do maint when they break
and they will
what is the O2 sensor output voltages?
cleaning them is great,usless if you dont test the output when your done.
on twins the DES switch will reduce RPM on both engines if one goes into RPM reduction.
on a properly maintained rig you will never NEED a water pump.t-stats or poppit valve nor VST cleaning nor low pressure pump nor water seperator replacements as its done.

 

[Whalure]

Re: 2001 ox 66 250 hp twins acting up help

Rodbolt,

Thanks for the reply, I bought boat in august, and original problem happened when I was bringing it home. Not sure about previous owners maintance on the motors, thats why I had all the stuff done.

Whats the point of twins if the yamaha des switch wont let you plane boat on one motor, if one motor is acting up? I will ask mechanic if he tested the 02 sensor output voltage. What other Pm should be done on these motors now while I have it in the shop?

Thanks

 

[rodbolt]

Re: 2001 ox 66 250 hp twins acting up help

just dont run them till they quit, preventative maint is always cheaper than corrective.
the 3.1L motors tend to eat low pressure pumps, replace them every 3rd season just cause.
the O2 sensor maint is every 200 hours OR once per year.
after cleaning its imperative to check the output voltage. out put voltage must be checked in the water and in accordance with about 3 tech bullitens.
VST maint must be done at least yearly.
water pumps,T-stats and pressure grommet should be done yearly or at 200 hour intravels whichever comes first.
keep the power head sprayed down with fluid film or its eqivalent.
look in the marine technical guide, it has the maint schedule for your EFI motor.