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Post Info TOPIC: 2008+ Europe market Yamaha WR250X/R AIS/O2 and ECU


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2008+ Europe market Yamaha WR250X/R AIS/O2 and ECU


I have a great motard 2008 Yamaha WR250X, and I going to uncork bike's performance by doing AIRbox mod and Slip-on exhaust as described on many forums as well as at Yamaha's GYTR pages.

I've doing a small research to figure out why EU models of WR250X/R equipped so well (?) with narrow-band (found info somewhere) O2 sensor and how it affect Fuel Injection while bike is running to do a "smart" upgrade, not just cut one piece and install another by step-by-step instructions.


Many USA/JP bike owners first of all remove their AIS/Flapper/EXUP systems as useless prior to installing aftermarket exhaust and some fuel programmer. Almost all manufacturers of fuel programmers/commanders says that their products can't be used with EU models ( - "Note: NOT for European models with O2 Optimizer.").

Question: O2 Optimizer? Optimizer of what? With AIS? To get lambda=1 for CAT? What is O2 sensor is getting at idle? Do O2 sensor used to control Air/Fuel mix then AIS in insufficient (at 3000+ RPM)

This is a cut from official EU Yamaha's service manual:


and no mention of O2 sensor..

AIS, another interesting thing. It injecting fresh air to exhaust to help burn fuel in CAT. Effective RPM range while WR250X's AIS type can do their job - under 2-3x1000 RPM, so this is the range there O2 sensor can be used..

AIS - pulse(aspirator) type, as Wikipedia says:

The aspirator provided advantages in cost, weight, packaging, and simplicity compared to the pump, but the aspirator functions only at idle and so admits significantly less air within a significantly narrower range of engine speeds compared to a pump. This system is still used on modern motorcycle engines, e.g. the Yamaha AIS (Air Injection System).

And why at least on EU models some systems duplicating each-other:

  1. CO tuning in diag mode - affecting idle speed a lot


  2. Idle screw - affecting idle speed too.

I've heard that disconnecting O2 sensor doesn't light up engine trouble light, as well as whole AIS disconnect (at lest this is true for WR250X/R).

My thoughts is that similar architecture of pollution components can be found for each FI model of Yamaha, so may be any can give me a ray of light in this dark dumb questions..

Thank you in advance!

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