:agree: with your assessment that your dealer missed the mark. Your situation needs further analysis. An air leak upstream of the sensor would trigger an overly rich condition if there is a large enough leak and enough vacuum for the leak to pull air into the pipe. If the gas velocity was insufficient to cause a vacuum and pull air into the pipe, or if the leak was huge, the sensor might not have much exhaust passing by it, and the accumulating gases could cause it to go lean on the mixture. This seems unlikely. Small exhaust leaks usually have little effect on the mixture, IMO.
The first time this happened, the mechanic commented on the noise of the exhaust (I thought that it was just getting a nice burble), and so went looking for an exhaust leak.
The next time was right after the rebuild, and I assumed that the gaskets had been damaged. I had bought some Honda gaskets the first time (because there was a six week back order queue for the standard parts). I read in another thread recently that the Honda parts are a bit tricky to fit, so they might have been damaged. They were replaced with genuine parts.
In addition, a single O2 sensor in a combined pipe will not cause only one cylinder to go either rich or lean, it will affect both cylinders. Even if the leak is only in one of the cylinder's exhaust pipe, this is true, since the sensor reads the combined exhaust gas. It takes separate O2 sensors in separate pipes to affect a single cylinder or bank.
There are a lot of variables here, including the condition of the ignition system, the injector condition, and whether or not you have any mods. Tough to diagnose remotely, but they have jumped to conclusions, and they need to look a little further.
Yes, BUT... Every time they replace the Y pipe gaskets, the problem goes away. :dontknow:
What caused the previous engine seizing problem? If they did not isolate the cause, it could still be affecting your engine.
Another kinda mystery, NancysToy. The story that I took away was that a tooth was broken on second gear, and that debris from this got caught in an oil gallery and starved the motor.
I was brought up to believe that that was the kind of thing that oil filters were meant to prevent. I suppose if there was a *lot* of debris, then the filter would have been blocked, and the bypass operated.
It happened soon (like about 1000km) after the 20000km service, and there was no mention of debris in the reservoir gauze or in the oil in the service report.
It was unusual enough for a visiting engineer from Can Am to take pics of the internals.
My concern with the current blipper malfunction is that not matching the engine speed to the wheel speed on downshifts could have caused the broken gear tooth, so it might have been a long standing problem, and it might well happen again before we get a fix.