O2 sensor and closed loop operation? O2 sensor voltages?

Hello all,

So it seems our bikes are fitted with an O2 sensor from the factory (non USA models) don't run in closed loop at all. I've no idea what the O2 sensor actually does as it appears to be completely ignored and it runs rich all the time anyway. ~0.93v or so when measuring the voltage of the o2 sensor during cruise / light load conditions when fully warmed up. From what I can gather this means it's running very rich all the time.

I am using a Denso O2 sensor from another Yamaha which on appearance is exactly the same, two wire (blue and white) - so I don't think this would matter at all as I believe all o2 sensors run the same voltage range?

During deceleration with the fuel cut-off the voltage goes to around 0.2-0.4v. When adjusting the CO offset in the diagnostic menu I can see it go leaner or richer - so I now have the correct fueling below 2k RPM but above that goes to ~0.93v.

I've checked and the ambient air sensor and other sensors all seem to be reporting OK.

Has anyone else measured the voltage of the o2 sensor whilst running?

Many thanks,

Laurence

LaurenceGough wrote:

So it seems our bikes are fitted with an O2 sensor from the factory (non USA models) don't run in closed loop at all.

They do run in closed loop but only during steady state; during hard acceleration the air/fuel ratio is ignored (and that is true of all vehicles, not just motorcycles).

How did you determine that the bike is running rich? Is your mileage particularly bad?

johnkol wrote:

LaurenceGough wrote:

So it seems our bikes are fitted with an O2 sensor from the factory (non USA models) don't run in closed loop at all.

They do run in closed loop but only during steady state; during hard acceleration the air/fuel ratio is ignored (and that is true of all vehicles, not just motorcycles).

How did you determine that the bike is running rich? Is your mileage particularly bad?

Hi Johnkol,

Understood, as mentioned even during cruise / light load steady conditions the voltage is around 0.93v on the o2 sensor which is how I determined it is running rich.

May I ask how you know it runs in closed loop? That is the theory, as you say with most vehicles, but I've yet to see anyone with evidence on our bikes, it'd be awesome to know because I cannot find anything.

The milage is not too amazing, but it does have a Q4 exhaust and FMF powerbomb header, but it shouldn't make much difference if the o2 sensor was working.

Thanks

I don't know that it is running in closed loop, but that's the only reason to put a lambda sensor on an engine: to be able to run it in closed loop. Is it possible that Yamaha put a lambda sensor on Euro bikes just for giggles? Sure, but not very likely.

Mileage on the WRR can differ wildly depending on modifications: people have reported more than 80 mpg on a stock motor, yet others get  low 50s with an open airbox + fuel programmer + free flow exhaust, and none of them could be running rich. If you are below 50 though, then you are almost certainly running rich.

The only way to really know your air/fuel ratio is to take the bike to a tuner; if you have a fuel programmer, they will be able to adjust it for optimal performance and mileage. Alternatively, it can be measured during your MOT test.

Yes I too was thinking why would Yamaha fit one then, it doesn't make sense.

I was thinking actually, perhaps the previous owner fitted an aftermarket fuel pump or regulator as I believe the 2008 model sometimes had some issues with that. And as the quantum aftermarket regulator runs at 55 psi vs 35.6 psi it should be it might be running too rich due to this. I also need to find a better way to test the MAP sensor as that's a trickier one to test.

The bike runs just fine and seems to make great power so it cannot be too bad, but it's just on the rich side.

It might be too far off for the ECU to adjust.

If there is an aftermarket fuel regulator (and no fuel tuner to compensate) then you are definitely running rich; when I replaced mine the mileage dropped by 15%. Couldn't you check with the previous owner?

Be careful with measuring the sensors: the free service manual may not have the correct values, so even if a sensor measures outside the limits, it could still be good. E.g. while troubleshooting an engine problem, I found my air temperature sensor was outside the limits, got a new one, and that one too measured exactly the same; it turned out that both were functioning properly and the problem was somewhere else.