Question about O2 Sensor on '97 OX-66 250

[FishJack]

New Member - Great Forum!!

I have a (1997) OX-66 Fuel Injected S250TXRV - It still has the original O2 Sensor. I have read just about every post on this site and it appears that several upgrades have been made to the O2 sensor and some tube behind it?? Anyway I have taken my O2 sensor off and cleaned it in an attempt to improve the slow idle (1000-1200rpm)and the surge when breaking the 2000rpm range. I belive this engine runs on 4 cyl below 2000 then kicks in all 6 above 2000rpm but the surge has gotten a lot more noticable.

Should I fork up the bucks and replace the O2 and tube? Or just attempt to clean again.
It also has the original t-stats should I replace them as well? and any other parts - The motor has about 500-600 hours.

Thanks and sorry for the long post..

Jack
Gulfport, MS

[boats.net]

Your dealer can test it with a volt meter while running or you can replace it, which it probably needs to be replaced.

[Ken]

Jack,
Welcome to the forum - if you are going to be doing your own maintenance, get yourself a Yamaha shop manual - go to www.yamahapubs.com and they will deliver to your door.
You can remove the thermostats and clean and test them per the manual - might save you a few bucks. Also, be sure to use new thermo cover gaskets when re-install.
If it has been at least three years since last water pump repair, you might want to consider it -even if you have good water pressure, the lower unit bolts can corrode fairly quickly in salt water. Be sure to use a good quality bolt thread sealer (I use Permatex 14A thread sealer with Teflon) where indicated per the manual.
Good luck,
Ken K

[FishJack]

Thanks Ken
Yes I do all my own maint/repair and already have the Yamaha shop manual for my 250.. I am going to test the O2 sensor tonight. Testing voltage as per the manual. While I'm at it I guess I'll remove the thermostats and test as well.

After starting this thread last night I ran across this online -

http://www.boatsetup.com/O2sensor.pdf

Might try his technique to clean/test..
From what the local dealer tells me the only upgrade was to the tube that vents the #1 cyl to the O2 sensor.

Thanks again.. Will post back with results.

[FishJack]

I removed the O2 sensor cleaned the carbon off the vented housing with the assistance of Ring-Free and a copper brush - tested the O2 sensor with a multi-meter and it tested fine (well within spec). The plastic cover that is on the O2 sensor had a good bit of black oil in the bottom and it had soaked into the foil/foam insulation??

Is this normal? I got all the oil out of the housing that I could.

I also removed the tube that feeds the O2 sensor from the #1 cyl - it was clear but had some carbon build up so I cleaned it as well.

Re-installed the O2 assembly - ran the motor on the trailer. I know that this is not a good test. I will have to water test sometime in the next couple of days. Did "seem" to idle better though.
Thanks,
Jack