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Old 09-09-2008, 02:50 PM   #11
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Joined: Apr 2003
Location: Long Beach, CA
Oddometer: 11,887

Originally Posted by Carlos M
I had to sketch this to completely figure the whole thing
Well done. I'm sure that drawing will explain things for a lot of people.

I now understand why the two sensors at the Hall sensor plate!
That's it. Do you see how either of the cylinders can be removed to form a single cylinder motor, and the ECU operation stays exactly the same? Something else... 2, 3 or 4 Motronics can operate a flat-4, flat-6 or flat-8 motor. The only wiring change is the Hall sensor wires to one (or 2 on the flat-8) of the Motronics are swapped (TDC-for-BDC) because some pairs of pistons are 180 'out of phase'.

And thanks Grok and MJS, I was having the same doubt as Terry.

I had no idea that half the injection was being made into a closed admission duct... it sounds somehow inefficient.
The fuel sits for 1/2 a combustion cycle in the intake tract and vaporizes. The fuel must vaporize to be burned. What doesn't vaporize sits on the intake tract walls in sort of a 'film reservoir' and evaporates at a rate according to the conditions in the manifold. (Wall temperature, manifold pressure, and intake airspeed.) The quantity of fuel in the 'film reservoir', and the vaporization rate, is calculated by the ECU. All of the fuel injected eventually makes it into the cylinder, but there is sort of a 'variable delay period' in the fuel film reservoir on the intake tract walls.

The identical fuel film effect happens with carburetors, though a carburetor cannot dynamically adjust itself to account for the fuel fuel film reservoir and as a result performance, efficiency and emissions each suffer to a degree.

If you want to find out more about the above, here is what's considered one of the best primers on the topic: US Patent 4,388,906.pdf

Now let's move to the Hexhead... ... Has the hexhead moved away from batch ignition and wasted spark?
Yes, because of the camshaft sensor the new ECU on the 1200 motor operates the injection and ignition 'sequentially'. Or if not sequentially, at least with cylinder-to-cylinder differences in spark timing and injection duration. The main impact of this felt by the rider is more consistent crankshaft speed which makes for a smoother running motor. The 1200 also has a counter-balance shaft to reduce vibration. Smoothness and vibration are not the same thing.

I do not know if it does how many camshaft sensors?

Where are they?
Right side camshaft.

Can the bike work on some sort of limp mode without these?
Sure, though it really wouldn't 'limp' much. The ECU could operate with batch ignition and wasted spark. An industry standard for all motorcycle motors so far. Just recently moving to sequential fuel and spark because among other things the high rpms do not allow enough time for an ignition coil to charge up twice per combustion cycle.

- Jim


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Poolside screwed with this post 09-09-2008 at 02:55 PM
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