Originally Posted by BrianG
Sounds like somebody is missing the boat out there in "aftermarket land". Actually, I'd say they fell off the darn thing altogether.
The whole benefit of closed-loop EFI
is the fact that a computer can monitor a number of issues at the same time. It can then make the BEST changes to all of the parameters over which it has control, with the result being the best power and/or economy for a given situation, as determined by the fuel/ignition map programmed into the ECU.
Should any significant sensor input be lost, the ECU drops into "limp-home" mode, which is open-loop, and which is totally reliant on a predetermined fuel/ignition map that makes MANY assumptions, and therefore sub-optimal (usually rich and spark-retarded) settings.
Reverting to open loop EFI
is about as smart as reverting to carbs, since you lose the consideration for engine warm-up, and atmospheric conditions that the O2 sensor info provides. It might work OK for the conditions that it is designed in, but it can't possibly work as well in LA and Denver without map changes.
So these guys suggest that their conversion to open-loop EFI
is better than remapping the closed loop system?? That's simply GARBAGE! It might be easier to do, and it might work in some small and well controlled environment that can't resemble the real world. I'd say that Barnum was right!!
My understanding is that on the bikes, the O2 sensor is used to trim fuel ratio to stoichiometric, i.e. 14.7:1, under part-throttle/cruise conditions only. This is NOT the best ratio for making best power. It is the best ratio for emissions/fuel economy. It would seem that most knowledgeable tuners will go for an air/fuel ratio of about 12.5:1 - 12.7:1 for best performance/power. Fuel mileage will go down, but who give a
unless you bought your bike for commuting, in which case you probably wouldn't bother with something like a PCIII
in the first place.
If you really want to make best power/performance with a closed-loop system, you'll need a "wide-band" O2 sensor and a computer designed to work with it, such as Accel's DFI, FAST Electronics' or MOTEC's ([HOMER] mmmmm.... MOTEC[/HOMER]
) system. These systems are programmable to feed back info from the wide-band O2 that will tell the ECU exactly what ratio is being measured at the sensor.
This is unlike the standard O2 sensor, which is really only designed to tell the ECU if the fuel ratio is richer or leaner than stoich -- not the actual air/fuel ratio. The standard systems, even on most cars, do go into open-loop under full-throttle conditions. This is because 14.7:1 is too lean for full-power and will cause detonation problems and along with them, possible melt down.
w/o O2 sensor IS a better system for performance applications than the stock ECU w/sensor, as it will allow an experienced tuner with a wide-band O2 sensor and a dyno to run the bike under simulated load conditions. The tuner can then make changes to the open-loop fuel table/map to adjust for best performance. Yes, if anything major changes, and this would include altitude, it might need to be remapped. I say "might", as our bikes incorporate a "MAP" (Manifold Air Pressure, IIRC) sensor, that can adjust for altitude changes, as the pressure readings will change with changes in altitude.
As always, YMMV. And if anybody else (OnTheEdge) more knowledgeable about EFI
systems than myself would like to chime in to correct any of my possible errors, please do.