I'm moving my air temperature and pressure sensor from behind the headlight to on top of the airbox, where there are a couple of convenient unused threaded holes.
That got me thinking. The sensor itself is a Bosch MAP sensor - a manifold pressure and temperature sensor. It's designed to sense absolute manifold pressure, and the sensor element is even in a little tube with an O-ring, which is clearly designed to be plumbed up to the manifold.
This makes sense. If you're measuring things to work out how much fuel to inject, manifold vacuum and temperature are a good thing to know - there's a quite straightforward, direct relationship between the vacuum and temperature and the amount of air for each charge, making fuel metering easy.
But instead Ducati put this sensor outside the manifold, on a little purpose-made bracket behind the headlight, plumbed up to nothing. So it only measures ambient air pressure and temperature.
Does anyone know the reasoning here? Is it perhaps some sort of legacy thing, so they could use existing carburetted manifolds/airbox/whatever?
When are you going to put "Suzy" on the tank of that bike? ;)
IMO you are WAAAY overthinking this. Even a performance car gets by with one MAF and although the intake is common, the cylinders still don't all breathe the same, even with some intake tuning in the plenum. I only wish the bike had a knock sensor although Ducati probably found that unnecessary. Maybe an F1 car would benefit from each intake being metered, but the complexity makes my head spin.
Consider how different a bike is vs a car too. The engine is exposed to the elements and is air or air/oil cooled. Under the bonnet is a more stable environment for a car engine. My K-bike engine was almost there! 8) Water cooling and all.
Anyway, I doubt they use this method to save $10. Many other EFi twins also get by with simple ambient air measurement including my Triumph, so that MAP is doing what they need.
Since you are an accomplished engineer, if you had cold winters out there, it would be fascinating to see what "Suzy EFi" might be like! You might even be able to get both cylinders to run at the same temperature although I can't recall ever seeing my plug readings varying much between cylinders in any of the Dellorto fueled bikes I owned and maintained.
All speculation of course...
By Bosch part number it may come up as a MAP sensor, I never checked, but on your injection system it is used as an ambient air pressure sensor to help the EFI compensate for altitude change.
Not a legacy deal, as the carbie manifolds and airboxes are different from the EFI stuff.
The MM IAW5.9 ECU uses the ambient air temp and pressure (really for altitude) as a 'trim' on the mixture.
Seems you could mount it poking into the airbox, and it would give better mixture control.
My concern would be that the pressure fluctuations in the airbox would beat the air pressure sensor to death.
Or give a noisy signal to the ECU.
Or maybe it's filtered and has a near-infinite fatigue life.
Perhaps you could put a 'scope on it with it poked into the airbox and the engine running. ;D
(Geebus I type and think slow...)
Quote from: Speeddog on June 25, 2012, 09:20:38 PM
(Geebus I type and think slow...)
Think we can start a club then? 8)
Quote from: Curmudgeon on June 25, 2012, 09:28:40 PM
Think we can start a club then? 8)
Seems two of like mind is more coincidence than club. [laugh]
I'm not putting it _in_ the airbox, as then it'd read a lower pressure than ambient, and it'd lean the mixture out (which is the absolute last thing I need). I'll put it on top, with the little sensor orifice sticking up in the ambient air just in front of the snorkel.
It just struck me that they'd gone to great lengths to put the sensor in a really annoying place, right behind the headlight jammed in with every other cable in the sun, and I couldn't think of any reason why.
Quote from: suzyj on June 25, 2012, 10:26:12 PM
I'll put it on top, with the little sensor orifice sticking up in the ambient air just in front of the snorkel.
No idea whether it would make any difference but wouldn't it get a lot warmer sitting over a hot engine while parked vs having it behind the headlight?
Quote from: suzyj on June 25, 2012, 10:26:12 PM
I'm not putting it _in_ the airbox, as then it'd read a lower pressure than ambient, and it'd lean the mixture out (which is the absolute last thing I need). I'll put it on top, with the little sensor orifice sticking up in the ambient air just in front of the snorkel.
It just struck me that they'd gone to great lengths to put the sensor in a really annoying place, right behind the headlight jammed in with every other cable in the sun, and I couldn't think of any reason why.
Behind the headlight protects it from the wind and isolates it from engine/solar heat. Are there other places just as good? probably. The carbies with electric float bowl heaters had an ambient temperature sensor mounted there to keep the heaters off when not needed. That worked, why not continue? If you want to move it find a location that is quiet air and reflects ambient temperature.
THIS:
Quote from: howie on June 25, 2012, 09:18:42 PM
By Bosch part number it may come up as a MAP sensor, I never checked, but on your injection system it is used as an ambient air pressure sensor to help the EFI compensate for altitude change.
and THIS:
Quote from: howie on June 26, 2012, 04:11:23 AM
Behind the headlight protects it from the wind and isolates it from engine/solar heat. Are there other places just as good? probably. The carbies with electric float bowl heaters had an ambient temperature sensor mounted there to keep the heaters off when not needed. That worked, why not continue? If you want to move it find a location that is quiet air and reflects ambient temperature.
I'll just add that over the years there have been plenty of speed/density EFI systems that utilize an ambient pressure sensor instead of a "manifold" sensor, it's not that odd.
I'd definitely consider NOT relocating it as a hotter sensor is going to lean the mixture too.
i think it would definitely have been nice to have a map sensor on these bikes. i understand what the atmospheric pressure and temp are used for but with a map sensor we could run real tunes that have variables for revs, throttle %, and engine load! i believe that would improve the low end response and fueling on these bastard motors quite a lot. but it would require a less basic ecu and i suppose Ducati considered that an unnecessary expense.
but yeah, as I'm sure Suzy understands, putting this sensor into the manifold with its current setup would be bad. but if we could magically add a third fueling parameter and attribute it to this sensor i would love my bike just that little bit more.
makes me think, i wonder if my new Ignijet ecu can be set up to accept a map sensor...... [evil]