You don't necessarily need...
You don't necessarily need to know exactly what each sensor does. However, It's important to understand that that all of the sensors provide information that's correlated by the ECU, and that the ECU (#20) makes its fuel mapping selections based on that information. This system is fitted to the Kawasaki Versys 650 twin, and it's worth noting that the O2 sensor, (#19) is only installed on the European versions.
While most EFI systems operate in a similar fashion each one is a dedicated design fitted and mapped for a particular motorcycle. Fortunately, there's plenty of shared hardware to help keep costs manageable.
Yamaha, Suzuki and Kawasaki (with some exceptions) all seem to prefer Denso processors in conjunction with Keihin throttle bodies. Typically, at low speeds these systems use a Speed Density map, and shift over to an Alpha-N map at larger throttle openings. Normally these systems also utilize sequentially fired injectors and incorporate tip-over switches to kill the engine in the event of a get-off.
Kawasaki cruisers use/used a Mitsubishi ECU with a Keihin dual throat throttle body on their Vulcan 1500-1600 cruisers, though whether the latest versions still do I can't say. The Mitsubishi system, a Speed Density- Alpha-N, set up is particularly friendly to large V-Twins, so although I haven't tried to verify how many other bikes employ it, I wouldn't be surprised to find it's being widely used.
H-D uses a Delphi system and ironically, (or not, depending on your point of view,) it's likely the best, most sophisticated system in current use. Like the majority of EFI systems, it's a Speed Density to Alpha-N system, but one that can also operate in closed loop. Atypically it features ion sensing, which means it can use the spark plug as a sensor to tell it what's happening in the combustion chamber. This is a feature that no other EFI system uses-yet, and pretty much guarantees that H-D will be able to get their bikes through emission testing without problems for many more years.
There are also a few oddball systems out there, early Triumphs and the defunct Excelsior-Henderson used Sagem, a French brand now owned by Johnson Controls. New Triumphs, including the twins use Keihin throttle bodies and ECU's. BMW, of course, uses BOSCH and those guys won't tell you jack. Honda uses its own in-house brand called PGM-FI and last, but by no means, least there's the Magneti-Marelli system as used by Ducati.
Interested in more?
Try these:
Motorcycle Fuel Injection Handbook
- By Adam Wade, a lot to wade through, (pun intended), but extremely useful and more info per chapter than most of us can process at a single sitting.
Four Stroke Performance Tuning
- By A. Graham Bell. This one is car oriented but includes plenty of good solid info, and does have some motorcycle specific info included.