yamaha ox66 225 issues
 

i have a 2001 yamaha 225 ox66 that has been giving me trouble for a while now. intermittent issues randomly idles high in neutral, at low rpms chugs likes is missing and randomly at cursing speed will drop 2 to 3 hundred rpms and pick back up. cannot idle through no wake zones when its happening just chugs like crazy.
i have replaced spark plugs, vst filter, fuel filter on side of engine, fuel water sep filter. low pressure pumps, o2 sensor and cleaned out sniffer tube. will run fine for a day no issues then all of a sudden it will act up. any help would be appreciated.

Bad coils or wires maybe? Sounds ignition related to me.

Have you put a fuel pressure guage on it and checked the high pressure pump output? Idling high in nuetral and chugging under load sounds like fuel starvation to me.

ok so new low fuel pressure pumps new o2 sensor and good fuel pressure throught rpm range
seems like is dropping cylinders when its not supposed to
while it was acting up i pulled wires on the plugs and the top left and bottom right were not firing

I have been plagued with a very similar problem recently with my ox66. I was absolutely certain I found the problem by cleaning my injectors, but nope as of yesterday the problem is back, and that's why I'm up at 4am frankly.. it's got me losing sleep over it. !! I will now be putting a pressure gauge on it and see what that brings as Ferm suggests, but just because I decided to check my work and go over everything I've done already yesterday I pulled all 6 new spark plugs and found the bottom right ( not sure what number cylinder) plug to be spotless unlike the other 5, which makes me think it could be as Bradford mentions ,I'll let ya know.

I'm no expert but I do know that the OX66s don't idle in neutral on all cylinders. They purposely shut some down.

that ive seen but no body can come to a consensus on how it actually works.
changed the pllugs and ran great trolling and running for most of the day then started acting up again on the way home to the point of coming off plane.
at my limits with this motor not sure where to go from here.

Any progress? Always interested in any knowledge I can gain about OX66s.

You don't get buzzers or alarms...your buzzer works?

Could this be related to temperature? You say it runs great for a while...is it always good cold?
Maybe electronics acting up when hot?
Maybe an electrical connection?

Try a can of electronics freeze spray on various parts when it acts up.
(a can of "computer dust cleaner" will work in a pinch, its pretty cold).

What is the output of the regulator? greater than 12.8V?

the next step i am taking is to send the injectors off to injector rehab and have them gone through. i have checked and cleaned all grounds and power terminals on the motor and battery. does not drop below 12.8 at all and its just so random when it does act up. sometimes its from the time i start it up first thing sometimes i can go days without any thing happening. sometimes it comes and goes in the same day. it doesnt seem to make a difference between hot and cold temps. until recently this motor has been 100% reliable.

been a while but i sent the injectors off to be professionally cleaned in December of 2018 and have never had a problem since.