225 ox66 alternate o2 sensor success... so far

[family affair]

Issue: rich running engine
Diagnosis: possibly o2 sensor, but it almost passed most of the Yamaha service manual checks.
Result: being hesitant to try a $300 part that might not take care of the issue, we searched for alternatives. A $42 NTK o2 sensor of almost identical design has greatly improved fuel consumption, nearly eliminated smoke at idle, allowed us to hit max rpm, and eliminated surging... amongst other things.
Knowing this part can foul from low speed operation, being able to replace the sensor for a resonable price makes owning this engine more tolerable.
Hopefully this will help others struggling with engine diagnosis.

 

[seasick]

What was the model number and what do you mean by original sensor passed MOST Yamaha checks. There aren't a lot, two perhaps.

 

[family affair]

NTK 21006
The old sensor passed the flame test. It also read between .5 and .6 volts when the engine was warm. It did not however increase voltage when I placed my finger over the #1 cylinder throttle plate bleed hole.

 

[seasick]

NTK 21006
The old sensor passed the flame test. It also read between .5 and .6 volts when the engine was warm. It did not however increase voltage when I placed my finger over the #1 cylinder throttle plate bleed hole.

 

[Tucker]

I'm running the same sensor. Passed idle tests but have not yet run the high speed test: 3000-3500 RPM, .3volts steady. Have you performed this test yet family?? Sounds like it should pass with flying colors. Need the long test harness though. I'd like to get a couple old sensors, splice in the $42 jobs every year. One of the most cost effective maintenance chores we OX66 owners can do.

 

[family affair]

Tuck,
Some might regard it as reckless, but I did not test voltage at high rpm. There are only so many ways to make an o2 sensor like ours. I'm not worried about it. We ran 20 miles at 4200. Flawless operation. You have read posts from others doing this. Not a single one has had an issue.
As long as you have made quality connections you should be good to go. Even of you didn't the worst that should happen is high fuel consumption. The system is fail safe.

 

[Tucker]

Family not sure where you got the info for that sensor. I got mine from a long thread on THT and learned a lot. There are 2-types and this thread had lots of posts differentiating the 2. I agree and think you got the correct one. But, be advised: If the Yamaha ECU detects a no-signal or bad-signal it richens the mixture to about 4000 RPM's, then leans the mixture. Running at high RPM with the wrong 02 sensor or a bad one could burn pistons. Since you ran at 4200 for 20-miles it's probably safe to say you nailed it. It's just my cynical nature when dealing with aftermarked parts to be tight-ass. I have the long test harness and will report on the running test shortly. I am impressed with your trouble shooting procedures though. I bet most guys would have moved onto something else after it passed the flame test. My symptoms were'nt as extensive. I could achieve max RPM but fuel burn was twice that of the good engine, no surging. Strange beast this 02 sensor....

 

[family affair]

But, be advised: If the Yamaha ECU detects a no-signal or bad-signal it richens the mixture to about 4000 RPM's, then leans the mixture.

Is this in the Yamaha service manual? I have read about this on other forums, but have not been able to find anything in print regarding this statement. I can't find anything on this in my SELOC and I have practically read half of it! I would be surprised that the default fuel map (without an O2 reading) would run lean enough to risk engine damage. On a car the system resorts back to reading off the MAF, TPS, and IAT. Since this engine is without an MAF, I would think a fail safe design would simply resort to throttle position and air temp.?

I bet most guys would have moved onto something else after it passed the flame test.

The story is long, but we took care of about every other part before resorting to the O2. I still suspected it bc the engine was running so rich that the engine was guzzling gas, smoked more than what I thought was reasonable, and every plug was soaked! What also sealed the deal was a Yamaha tech that told me he has come across OX66's that had good O2 sensor readings, but still caused the engine to run bad. Replacing the O2 sensor in those cases resolved the running issue after eliminating all other possibilities.

Something else I learned is that TPS is ridiculously sensitive! You can tap that baby with a screw driver after tightening it down and it will affect the signal. Spot on TPS=better running engine!

 

[Tucker]

These OX66's are different than a car. Cars uses MAF and IAC. The OX66 is strickly speed and density. I've also read this on several forums. No, the manuals don't say anything about that. Hee, hee, know what you mean about reading half the book. I got the Yamaha shop manual under my bed and read it to sleep. Wife thinks I'm nuts...

 

[Tucker]

Yea, and no kidding on the TPS! First time I did it took about 15-minutes per engine. Get it right on .5 and the freaking thing would move when I tighten down the screw. You poped off the throttle linkage to fully close the butterfly right?

 

[family affair]

Yes I did take the linkage off to set the tps. I actually reset all of the throttle plates. Believe it or not, they were not set correctly from the factory. Each plate was very slightly opened.

 

[Tucker]

Yes I did take the linkage off to set the tps. I actually reset all of the throttle plates. Believe it or not, they were not set correctly from the factory. Each plate was very slightly opened.

They're suppose to be slighly open with linkage connected. Idle adjustment screw should be out about 1-1/2 turns.

 

[family affair]

I know what you mean. With the idle screw backed out and the linkage disconnected, some of the plates were still slightly opened. My dad didn't believe me till he saw it himself.