PCIII O2 Sensor bypass

[mlm]

I got a PCIII USB on my 06 F4i a few months back. Part of the installation was to disconnect the O2 sensor. From what I understand, the factory computer uses the O2 sensor to lean out the mix, which is a good thing for emissions and fuel economy.

The bike is stock. Got the PC partly to get better throttle response, possibly get a minor increase in midrange, and to play with. Using the stock (not neutral) map for now, and noticed the fuel economy dropped slightly. Was hoping that putting the O2 sensor back in the loop would rasie it back up.

I'm guessing the only effect would be that the factory ECU would
lean out the mix on steady throttle. I thought I read there was a lag on the correction, so any gains in resposne and midrange should be retained...just a loss on WFO which doesn't concern me.

Is there any chance this could do any damage? Biggest worry is that it could make the bike run too hot?

[paroxysm]

be very careful when leaning out your bike. In my mind plugging the 02 into the stock ECU would lean out what the PC has already taken care of.

Though, don't ask me, 'cause I've had a PC for 20,000 miles without getting it tuned :) It ran GREAT until I took the smog stuff off (stopped backfiring...) but my fuel economy took a shit. I'm finally taking it in this weekend to get a map done.

[mlm]

I've been reading some more which is making me think I should go ahead and reconnect the O2 sensor. Someone let me know if any of this sounds wrong:

1) OEM ECU will use the O2 sensor to lean out the mix to 14.7 when throttle is closed or slightly open.

2) PCIII is a closed loop system (doesn't self adjust). Just increases or decreases the amount of fuel injected at a given RPM and throttle position.

3) Oxygen sensor will interfere with dyno tuning the PC since it would keep negating any fuel increase mapped in at low RPMs.

[insider]

Dynojet sells the 02 Eliminator plugs to set the stock sensor readings

[mlm]

Originally posted by insider
Dynojet sells the 02 Eliminator plugs to set the stock sensor readings
Thanks for the reply, but please explain.

I'm still getting conflicting information on the web. My main concern is getting back fuel economy while retaining some midrange and throttle response improvements.

[insider]

With a PCIII installed you have to expect fuel economy losses. All the thing does is to dump extra gas into Combustion.

Remember, a PCIII is used to enhance performance, the only way to get more bang out of the cylinder is to stuff more gas into it....

What makes you think the bike is running lean? Have you had an experienced eye to look at the plugs?

The o2 sensor plugs always sends the o2 values to a perfect condition for Stoichiometric Combustion. This aids in smoothing out throttle response.

[mlm]

Question answered from Dynojets web site. I feel kinda stupid for not seeing this the first time.

http://www.powercommander.com/powercommander_iii_usb/powercommander_faqs.aspx
My Power Commander came with O2 eliminators, should I use these and what are they?
On bikes that use an O2 sensor in the stock exhaust have a closed loop area that can not be adjusted by the Power Commander alone. If you make adjustments with the PCIII in the closed loop area the O2 sensor will sense these changes and the ECM will alter the fuel curve accordingly. If you want to have full fuel control over the entire RPM range of your bike then you will need to bypass the closed loop area which the O2 eliminators will accomplish. If you are looking for the best fuel economy and not worried about making changed to the closed loop area you can leave the stock O2 sensors connected and still make changes outside of the closed loop area with the PCIII.

[Thirdnalga]

The O2 should do more than just lean the engine, it should also richen it when appropriate. It senses oxygen (duh) in the exhaust and from the amount it sees, send a 0-1v signal to the PCM from which the mixture is inferred. Closed loop is not a type of system, but rather a state of the system, meaning that it's getting feedback from the O2 which the PCM then sends to the Airflow or MAP sensor (however your bike is equipped) and then the cycle repeats (in a loop). Disconnecting it is fishy at best, if you ask me. Though I have no specific experience with PCIII, I can only imagine that you're just dumping fuel down the intake, now.

[Dopesick]

I can tell you 100% that if you DO NOT use the PCIII to lean the system out (further then stock would be a ludicrously BAD IDEA) you will NOT gain any better fuel mileage.

The realistic purpose of the PCIII is to adjust the fuel injection system to rid lean and rich spots in application to the modifications you have done to the bike. Otherwise a factory bike is just lean enough to pass import/export emissions qualifications.