OX66 O2 Sensor - Results Good or Bad?

[funtastic]

Cleaned my OX66 250 O2 sensor. The Tube was SOLID Carbon, took me over 30 minutes to get it out with varying drill bits! Black oil like substance in everything. Having owned the engine for the second year, I am doubting anyone ever cleaned it?
QUESTION - I ran Testing per the Standard O2 PDF. Results at Idle ran about .6 volts. Covering the hole caused it to increase about .1volt to .7volts. Removing finger from hole caused a quick second spike to .75/ .78 and back to .6 volts.
The Lowest Reading was .55 volts and the Highest reading was .78 volts.
Who can tell me if my O2 Sensor is operating correctly?
My gut is it is "Barely" working....and I felt I should have seen it much lower than .55 esp. after altering the airhole on #1 Cylinder?

 

[rodbolt]

Re: OX66 O2 Sensor - Results Good or Bad?

sounds like it overly maintained.
I hope you did not try to drill the passage in the block.
I do know where one OX66 motor is with a 1/8th hole in the piston skirt.
it should scale between .35 and about .65 if everything is working correctly.
engine MUST be at the proper operating temp,MUST be at the proper load,3000 to 3800,AND the gearcase must be submerged or most readings are worthless.
yours is working,cover the #1 air bypass hole and you force it rich, the O2 sensor wil react by showing .8 to .9V then will attempt to lean out the fuel.
uncover it and now its lean.
the sensor wil try to correct it again.
the ECU isnt smart enough to know someone is playing with the bypass air.
sensor maint is once per year OR every 200 hours,whichever occur FIRST.
that sensor can and will blow a piston if not maintained.

 

[funtastic]

Re: OX66 O2 Sensor - Results Good or Bad?

To clarify, I used a drill bit by hand to clear Carbon in the brass tube. I then had to chip off carbon from sensor tip.....still concerned at sludge that was still seeming to be inside of tip protective cover. (ps it's a 99 engine)
Test- lower unit was in water, I let it run at idle....revving engine to warm up. Are you telling me that unless I run it on the go at 3ooo+ rpm........that my testing at idle was unreliable?
Thus...run it on the go......and over 3000 rpm....if I don,t see voltage fluctuate between .3 to .6 volts.......the it's bad?
Thx

 

[rodbolt]

Re: OX66 O2 Sensor - Results Good or Bad?

its either bad or the engine has other issue if it doesnt scale.
glad it was just the tube, had a guy drill out the block pasage only to realize he drilled through the piston,luckily it didnt hit a ring and is still running about 5 years later.

 

[airwo.lf]

Re: OX66 O2 Sensor - Results Good or Bad?

where is the o2 sensor located?

 

[funtastic]

Re: OX66 O2 Sensor - Results Good or Bad?

Rodbolt, The engine is/has been running really well, 5500 to 5700 Rpm, the only signs I was dealing with were loosing 1000 Rpm at WOT from time to time......but not always. I replaced the 3 LP Fuel pumps (at least 1 leaking) and still had RPM loss here and there WOT only! My guess was the O2 was causing the RPM loss.....and likely why it is smoking at idle so much. I'm going to do a last test running open water at 3000+ to see if sensor will fluctuate outside of .55 to .75 Volts. Last question, Am I at risk for engine damage if the sensor is running as I've stated?

 

[rodbolt]

Re: OX66 O2 Sensor - Results Good or Bad?

most likly not.
your numbers indicate its working and on the rich side.
the higher the voltage the richer it is and the ecu tries to correct it slightly.
have you checked fuel rail pressure at the failure RPM and load?
have you checked/cleaned the injector filters?

 

[funtastic]

Re: OX66 O2 Sensor - Results Good or Bad?

Since I cleaned the O2 Sensor......at WOT it has NOT seen a loss of RPM. Fuel Injector screens,,,,,,,,no I have not cleaned them.....I haven't really seen any posts on how to clean them....but I think I recall it being a relatively easy task? I'll be puchasing the Yamaha Tech Manual this winter for sure!

 

[rodbolt]

Re: OX66 O2 Sensor - Results Good or Bad?

the manual wont help,it doesnt show the injector screens nor does yamaha offer them. you can use the mercruiser 7.4 MPI screens from about a 94 MPI engine.
or you can send them out for service.