power commander and O2 sensors

Have a pciii installed on a 2000. I havent removed the O2 sensor. Can someone tell me why i need to do this?

Ive read conflicting arguments for and against.

The O2 sensors are used by the ECU to run the bike in 'closed loop mode' at low revs and also at small throttle openings. Disabling it by bridging the connectors with a (IIRC) 300 ohm resistor stops the ECU from switching into closed loop mode, so the PCIII can control the fueling right across the range. FWIW, running the VFR just with the O2 sensors disabled and no PC is a huge improvement, because it eliminates the surging present at small constant throttle openings (which is either it running lean, or constantly adjusting the fueling back'n'forth). The other bonus is it eliminates the momentary hesitation when the bike switches from closed loop to mapped mode, which is almost dangerous when for example you tip into a slow speed corner. Unless you feather the clutch, the hesitation can cause the bike to drop into the corner a little. (Adjusting the throttle to have minimal throttle cable slack is also useful for this).

Enzed's reply is not wholly correct. The O2 sensors are only activated by the ECU in the upper gears at steady throttle openings. Thus they have NO impact on the use of a Power Commander. If the PC is say adding +15 fuel at any point its doing so regardless of what adjustments the closed loop makes. If its too rich according to the closed loop, then the ecu will try to reduce it, but it only has a limited range of adjustment !

Ok, they're both kinda right.  A Y2K VFR EFI has only MAP, TPS, AAT, RPM, & ECT sensors. It runs a closed loop only at steady throttle, regardless of what gear you're in.  During closed loop the EFI will try to optimize your fuel mixture for best fuel economy and lowest emissions.  If you are running a PC and leave the O2 sensors in and the O2 sensors read that you are running richer than what the ECU fuel map at that steady state is calling for, the ECU will try to lean out your mixture.  The PC3 is going to intercept this signal to your fuel injectors and change it by whatever you have that engine condition cell set for, in Mohawk's example +15.  The end result is you will be running slightly less fuel under these engine conditions because the ECU is trying to lean out the mixture.  Will it make a big difference?  Probably not if your PC3 adjustment is large enough at this setting; but regardless, it certainly isn't the mixture you originally had it programmed for at that setting because now the ECU is adding less and the PC3 is adding a fixed amount.

And what about those areas of the fuel adjustment map where the PC3 adjustments aren't large?  In those cases it will certainly make a difference in the smoothness of throttle response.  Taking your O2 sensors out of service is easy and costs less than a couple of bucks.  There is a write up here on VFRD using Radio Shack 350 ohm (i think) resistors and jumping 2 of the O2 sensor harness wires so the ECU reads that the heater circuit in the O2 sensor is working so you don't get a FI error code.

Hope this helps :tour: