1999 225 OX66 02 Sensor Testing

I have 2 of these outboards and this weekend I cleaned both sensors using the methods described in this forum. Although I didn't have a test harness, I soldered 2 test wires on each O2 sensor so I could read the voltage (across the black and grey wires). Once warming up they both settled in around 0.5v to 0.6v. When I plugged the top cyl throttle plate hole they only changed from, say 0.52v to 0.59v ... and when I unplugged the hole it swung to 0.50v and then selled in on 0.52v. From what I had read in the testing descriptions I was expecting a much larger voltage swing. Does this indicate I have 2 bad O2 sensors?

Re: 1999 225 OX66 02 Sensor Testing

your sensors have failed<br /> they went to long between cleanings or they just went south.<br /> happens with age<br />just idling it should constantly scale between anout .4 and .7 v. with the air hole plugged it should go to about .9v then go to .3v or so after the air hole is unplugged. if they have not been cleaned then remove the o2 sensor and holder. soak the sensor tip in a capful of combustion chamber cleaner. soak the holder and draw tube in a carb dip basket. DO NOT allow the crimped portion of the sensor to be submerged or it will Drown. the sensors are about 325 dollars or so.takes 15 dollars worth of gaskets to clean and a torque wrench and the proper sized adapter on the sensor. pay careful attention to the draw tubes as they do tend to clog.

Re: 1999 225 OX66 02 Sensor Testing

Thanks rodbolt,<br /> I cleaned them as you described using the Yamaha spray decarbon stuff. The draw tubes which were clear and the holder had carbon but not too excessive. The testing I ran was at idle and on flush muffs. Both sensors acted the same. The sensors cleaned up good and the "tip" inside the shield has a brownish color. Looks like I'm out 700 bucks or so fo new ones.