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In a vein attempt to isolate the poor performance of my 1998 ox-66, and with the help of this forum and Google, I just pulled and checked my O2 sensor per the downloaded instructions. After removal, I couldn't help noticing that the bottom portion of the sensor was completely black with what appeared to be wet oily carbon. More oily than carbon though. Upon inspecting the O2 block, I noticed it is all gummed up with wet oily carbon throughout. While there are schools of thought on cleaning an O2 sensor, is it your best advise to replace it?, it does appear to be well-used. No knowledge of age. Also would like to know if my 1998 Yamaha 225 2 stroke ox-66 has a drawtube in the block behind the O2 plate? The O2 removal instructions I have states that removal and inspection of the drawtube was needed. When removing O2 assembly, I did not see one in the block. Additionally, when the mechanic rebuilt the powerhead, he over oil'd it pretty good, for the break-in period, I mean lotz of oil! I read that mega quantities of oil after rebuild can render the O2 sensor useless due to the oil signal sent to the ecu, thereby breaking up the motor, quite like 90% of the symptoms I am having regarding poor performance,rpm loss etc... What are your thoughts on this issue with the O2 sensor, and if you agree with replacement without testing due to its present condition, where is the least expensive place to find one. I am finding them in the 300.00 range. Thank you for your dedication to us boaters.
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make sure you use the correct O2 sensor holder parts at reassembly, as a runing change in mid 2003 the holder and attaching gaskets changed.
if the block has ben replaced since 03 the original parts wont work correctly.
if the insulation in the cover is contaminated it MUST be replaced.
I would clean and test your setup and find/replace the draw tube.
that o2 sensor is simply a fuel trim.
only signal the ECU recieves from the O2 sensor is the oxygen density in the exhaust.
there are no failure codes associated with the O2 sensor.
if its dissconnected the ECU fixs fuel rich at low speed and lean above 4000 RPM.
DO NOT run above 4000 RPM with a defective or dissconected sensor. -
1998 yamaha O2 sensor
Can I compression test the motor with the O2 sensor off the motor?, and do you recommend that ALL plugs be removed and WOT, prior to testing cylinder pressure?Comment
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