OX 66 occasional surge

[scofflaw]

2001 sx225txrz. Intermittent surge between 3300 and 4000 rpm. Will go up and down on its own. Holds nice and steady above and below those speeds. Filters nice and clean. Have cleaned O2 sensor but did not test it. Could the O2 be the culprit here ? Would a cheap replacement work as well ? Like ngk/ntk 21006

[panasonic]

2001 sx225txrz. Intermittent surge between 3300 and 4000 rpm. Will go up and down on its own. Holds nice and steady above and below those speeds. Filters nice and clean. Have cleaned O2 sensor but did not test it. Could the O2 be the culprit here ? Would a cheap replacement work as well ? Like ngk/ntk 21006

I don't know if that is your problem. But as for the O2 sensor, does it have anything stamped on it? NGK or NTK are the same company. I don't know for sure but NGK probably supplies Yamaha with their O2 sensors.

I would Google any numbers seen on the original sensor and see what comes up.

[panasonic]

Here's what Rodbolt said about testing O2 sensors on another thread.Not sure if this is applicable to your engine or not. Good information though.




over time Yamaha found the flame test not very accurate.
that's why there are running tests to properly observe O2 sensor voltage.
one is at idle gear case submerged and engine at operating temp.
with the air box removed and the engine at normal temp cover the #1 cyl idle air bypass hole with a finger.
O2 sensor voltage should rapidly climb above about .8V.
remove the finger and it should drop to about .3V then start scaling between about .35 and about .65 V.
the other is a constant run at about 3000-3500 RPM and watching the O2 sensor voltage.
should scale in the .35V range.

[scofflaw]

Trying to get Rod Bolts attention on this one

Also if anyone has any OX test equipment they want to part with , I'm interested

[rodbolt17]

paper clips and a digital meter and some wire works.
I would hook it all up and run it at the failure speed and load and watch what the output is.

should vary between about .35 and .6V.

[scofflaw]

So to recap this...It is possible a bad O2 can cause these symptom in this 3300 to 4000 rpm range ? Don't own that winky blinky device yet, but since my idle rpm is 700 can I assume that I have no bad sensors ?

This engine never goes into a higher cold idle mode if that is any clue or not.

Thanks for looking

[rodbolt17]

the O2 sensor is not monitored for codes.
that motor should start cold at about 1200 then drop back as the engine goes above 113*F.

[scofflaw]

What could be causing the no high cold idle ? The boat is in SW Florida so that's not really a big deal. The surging can be annoying though

[99yam40]

I would think if the motor thought it was warmed up already it would not idle high for the cold fast idle.
Check the temp senders that talk to the ECU

[scofflaw]

I would think if the motor thought it was warmed up already it would not idle high for the cold fast idle.
Check the temp senders that talk to the ECU

Good point, Looks like 2 of them on my motor. Apparently they should ohm at 54-69 ohms at 68*. Don't have a measurement for 113* when ECU switches.

New plugs, CS

[Punch953]

I know the motors are way different but my Precision Blend 200 had the exact problem. I had a bad fuel pump.

[scofflaw]

Update....have confirmed that the O2 voltage values are out of spec. in my problem area. Seeing this is an old boat and motor, I'm attempting to cheap my way out with an O2 sensor that costs less than 10% of what Yamaha wants.
Will update again when installed and running