WR450F 2012 real time AFR


26 replies to this topic
  • Texas2Smoker

Posted February 03, 2016 - 11:55 PM

#21

It's a weird setup, using a closed loop Lambda sensor capable ECU to run in open loop mode, w/o any feedback regarding AFR she's producing, but apparently the accuracy of the MAP sensor combinend with TPS and a lot of test runs enabled YAMAHA to create mappings/algorithms that produce a very stable carburator impersonation.

Regarding hot start: That's exactly what I had to endure. Before taking the to me new bike onto one week of off road vacation to Italy, I "fine tuned" the CO setting some 5 notch towards rich, because I've read so on the net and wanted to improve hot start.
That week was a dreadful torture. Bike would mostly start on third(!) button stab or first kick in neutral.
I tried a lot of e-start procedures, including but not limited to rolling on the throttle, holding it open a tad like in TT600 times, blipping it etc.etc.
Buddy on 450EXC would shook his head at my sorry e-start attempts on my then new bike, courteously not commenting on YAMAHA vs. e-start.

Things became happy again only after returning home and playing with the FI diagnostic tool in the direction of what I then regarded as "crazily lean".
Today I know better, and in hindsight find it amazing, that the bike back then did startup by button press at al.

I'm just wondering how the bike accounts for elevation and adjusts accordingly in extreme changes without an O2 sensor.

  • chu

Posted February 04, 2016 - 01:27 AM

#22

The O2 level is estimated from the intake air temp and MAP sensors rather than measured.  The ECU doesn't know if it's running rich or lean without an O2 sensor, it just does what it's programmed to do.



  • WRF-Rowdy

Posted February 04, 2016 - 03:04 AM

#23

I'm just wondering how the bike accounts for elevation and adjusts accordingly in extreme changes without an O2 sensor.

The map sensor's output is absolute pressure, hence elevation measurement can be done

"while the crank stands still" e.g. at every stall or after ignition on and before start.

Maybe even "right before " the intake valves open one could measure "static" intake pressure,

but I doubt that at higher rpms the intake tract airpressure has enough time to settle to ambient pressure.



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  • chu

Posted February 04, 2016 - 02:27 PM

#24

The ambient pressure will always have an effect on the manifold pressure though.  If you're running at zero vacuum at sea level there's going to be a higher MAP voltage than there would be running zero vacuum on top of a mountain.



  • Texas2Smoker

Posted February 04, 2016 - 06:12 PM

#25

Ok yall lost me

  • chu

Posted February 05, 2016 - 06:56 AM

#26

A MAP sensor is like a barometer.  It measures the air pressure.  A vacuum guage measures the difference between manifold pressure and atmospheric pressure.  So with the bike just sitting there with the engine off, a vacuum guage would read zero no matter if it was on top of a mountain or at sea level.  The MAP sensor would read whatever the barometric pressure is.  If the bike is pulling 5 psi of vacuum the MAP sensor subtracts that from the ambient pressure.  So the MAP reading would be higher at sea level than on top of a mountain even though both would be 5 psi vacuum.
 



  • Bass Mechanic

Posted February 05, 2016 - 09:24 PM

#27

A MAP sensor is like a barometer. It measures the air pressure. A vacuum guage measures the difference between manifold pressure and atmospheric pressure. So with the bike just sitting there with the engine off, a vacuum guage would read zero no matter if it was on top of a mountain or at sea level. The MAP sensor would read whatever the barometric pressure is. If the bike is pulling 5 psi of vacuum the MAP sensor subtracts that from the ambient pressure. So the MAP reading would be higher at sea level than on top of a mountain even though both would be 5 psi vacuum.

What chu is trying to say is that a vacuum gauge is a relative measurement it is manifold pressure relative to ambient or actual pressure.
Where as a MAP is absolute (manifold absolute pressure)
At sea level and at 15 degrees Celsius standard sea level pressure is 29.92 inches of mercury.
If temperature changes it will affect the density of air
We use this measurement as a reference standard of air pressure.
As you go up in altitude the pressure drops.

When your talking about a vacuum there really is no such thing as a vacuum unless you have removed all the air but we refer to a vacuum when the pressure inside is less than outside a container. But in reality the pressure relationship between inside and outside is just different.
To make things easier let's say that 29.92 inches of mercury is equal to about 14 psi

At my elevation we feel about 11 psi of air pressure. A vacuum gauge on an engine might show only 5 psi
The fact is 5 psi is still more than 0 so it still has pressure, just not as much as the outside (static) air pressure because when the piston goes down on the intake stroke it creates a larger internal volume and the air molecules have more space to occupy. So the density of the air decreases and thusly the pressure drops.
(The 5 psi is called a vacuum relative to static)
A MAP sensor is calibrated to read 0 in a complete vacuum so a map sensor reads exactly what the pressure is inside the intake manifold. If your at sea level and the throttle is wide open it will read 29.92 inhg or about 14 psi and when the throttle closes there is still some air getting past the throttle to allow the engine to idle and the same map sensor may only read 5 psi or about 10 inhg
But that is still a positive number so it is not a vacuum just a lower pressure than standard pressure.

A vacuum gauge on the other hand indicates a vacuum or more accurately a difference in pressure inside the intake verses outside the intake.

Mathematically if you have 2 map sensors,1 inside and 1 outside you can subtract the 2 values and end up with the same reading as a vacuum gauge.

Now getting back to the bike, I have not looked at the sensor diagram but in reality only a map sensor is needed to calculate the amount of air and fuel needed.

All you need to know to determine air density is the barometric pressure inside the manifold, the temperature and the humidity.
Those 3 things = the exact amount of air density. Since opening the throttle changes only the manifold pressure the humidity sensor is usually in the ecu and just needs a tiny hole to get the reading.
There is no need to get the barometric pressure of the ambient air because unless your trying to display a vacuum gauge this information is meaningless to the ecm.

The air temperature is usually read right after the air filter as it enters the engine so air density can be calculated.
Once calculated the ecm can inject the fuel necessary based on a programmed table that takes the air density and engine rpm into consideration and any additional tuning you have programmed into the tunable ecm with the power tuner.

As a pilot, we are taught to read manifold pressure (map)
the airplane displays the map on a gauge. The reason for this is that in a turbocharged airplane engine, the turbo is only there to restore the lost manifold pressure when at altitude, not to make additional power!
It fools the engine into performing as it would while still at sea level.
So if your at full power the gauge will still read 29.92 inches of manifold pressure and the engine still makes the rated power even at altitude.
Any pressure lower than this is expressed as % of rated power, it you might say the manifold pressure is 15 inches for example is about 50% of full power.
With this logic you can very accurately determine how much power the engine is making.




 
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