2003ox66 250 2 stroke high rpm.

[Millerc3]

Motor was cutting off while having run at idle for 10 to 30 minutes. No spit sputter. Taken to dealership and took them 2weeks to duplicate issue. They recommended a new wiring harness. ( based on the fact that they could get the motor to cut off by jiggling the wiring harness close to the ECU.) the wiring harness had to come from Japan and was on back order and would not be available til June 26. ( wiring harness is a 2 piece harness)
When I spoke to the technician he told me that there was a second issue and that was.. advanced timing that caused the motor to high idle(1500-1600 rpm and that it run at 1100 rpm after warm up and go no lower)
I couldn't wait till June 26 so I took the motor to some one else. He swore it was the ECU. So i had him replace the ECU and the wiring harness that attaches to it.
I thought it might be the TPS but everyone one said it checked out ( not sure if there are two TPS for this model)
This motor has been the most reliable one i have ever owned. Never had a problem. I guess it is my turn in the crapper.LOL.
I could use some help. ONE NOTE WHENEVER THE MOTOR CUTOFF AT IDLE IT WOULD IMMEDIATELY START BACK UP. CURRENTLY I DONT KNOW WHAT THE HECK IS GOING ON. Thanks

[99yam40]

well how does it run now that you replaced things?

[TownsendsFJR1300]

And the NOW high IDLE is since the first tech dinked with it?

It idled normally (short of stalling) before?

[Millerc3]

Millerc3

Before the tinkering the motor started at around 1300 rpm then down to 700 rpm when warmed up. Since parts change there has been no difference... still starts at 1500 and down to 11 when warmed up.
BTW this motor has always and still does start quickly on the first key turn.

[Millerc3]

Millerc3

And yes the motor idled normally with the exception of it randomly shutting down at idle. I would start out the day run about 10 miles to get bait ... idle back through the shallows to get to fishing hole and occasionally it would just cut off.

[99yam40]

Did any of these Yamaha techs hook the motor to a Lap top to see what it was seeing?

How did the last shop get the wiring harnesses if the 1st one had to wait for so long??

Does it still have advanced timing while this is happening?

[TownsendsFJR1300]

First, I would NOT operate the engine, shifting at 1,100 RPM's as that's really hard on the lower unit.

Someone else more knowledgeable will chime in and help...

[rodbolt17]

well if you buy a harness and ECU your most likely going to have spare parts.
use the Yamaha dealer locator function.
find a dealership with a master tech.
take it there.
there is no sensor that will stall the motor.
in fact any sensor you unplug will cause the ign timing to go to 7*BTDC and the idle speed to about 1100 RPM.

[Millerc3]

Millerc3

I took it to the dealership to begin with and they had it for 3 weeks . It came back with the high rpm issue and the fix was a new wiring harness which for that motor comes in two pieces. One they had and one was on back order from Japan and would not be available until June26 2017. I became suspicious when i went to the Pro Marine and inquired about the harness and they showed me on the computer where japan had more than five. I used the part number that the dealership gave me and we checked thru pro marine and it was the right number. I picked up the boat. The tech said it was running 7*btdc. He said the harness would fix it. At home i checked the motor and found a plug unplugged.
It had a pink,black,orange and a white wire. I plugged it in The motor still ran 1500 rpm.

[Millerc3]

Millerc3

I got the avail harness and took it to a local mech. To have it hooked up. I said he could wiggle the ecu and the rpm fluctuated. We replaced the one piece of harness and the ecu.. no change.
This is not the problem I had when I took it to the dealership.

[Millerc3]

Millerc3

Thanks Rodbolt. I will look for another dealership. I took it to the one that i originally purchased the motor at. They. Have done lions share of the maint.

[rodbolt17]

do they employ a master tech?

like I said any sensor left unplugged or failed or a bad harness will fix base ign timing at 7*BTDC and it will idle about 1100 RPM.
a quick check with the diagnostic test lamp will show what.
I would bet on either the fuel pump/wiring or the main relay. but first you gotta find the tech induced fault.

the master tech test is not like the old merc and jonnyrude stuff that was open book or avalible for purchase.
it is very tough,requires a minimum of 6 other courses before you can take the test. the test has about an 85% fail rate.
I took it and passed march of 06.
out of the 18 of us that qualified to take it only 4 passed that day.

most master tech's are rather anal about testing and they understand the systems and how they interact.

[Millerc3]

Millerc3

Ok will do.i will ask about the master tech thing. The tech I talked to also mentioned something about diodes that were burned out. Might have pertained to the he fuel pump but he said the 2 part harness was all i needed. I will. Talk to him one more time to get the story straight and look for master mechanic. Thanks again.

[rodbolt17]

only diodes I know of on that motor are contained in the regulator/rectifier.
there is a resistor for the fuel pump at low speeds(below 1200 RPM).