This is an interesting read for me as I had no idea other tuning devices removed the o2 sensors. ( I have a direct to ecm tune) I just replaced my 02 sensors yesterday. I was getting an occasional check engine light for the rear sensor and have noticed that it hasn't been running as well and my gas mileage has fallen off 3 or 4 mpg's. I assume that the computer is holding the default setting. Seeing how mine has fallen off with bad o2 sensor, I couldn't imagine taking them out of the tuning loop. As others had mentioned, the ecm will only know the map installed and wont be able to read the exhaust and compensate for anything different. With so many factors affecting the way the engine runs such as different brands of gas, air filter cleanliness, temperature, altitude, etc... why would you want to get rid of the 02 sensors preventing the computer making adjustments to get to the AFR you tuned it for? I'm dying to see how she runs tomorrow and get my gas mileage back.

 

Why would you want to get rid of the O2 sensors and run open loop? Good question.

The stock AFR table for my '09 Nightster is set to 14.6 almost throughout the entire map. This setting for AFR - 14.6 - is not only a set point for AFR, but it's also a switch that tells the ECM to run in closed loop (use the narrow band O2 sensors for feedback). This may make the EPA happy, but an AFR of 14.6 is not good (too lean) for most of the operating bands that the bike will find itself in. So, if you want to run the stock setup in closed loop, you have to run at 14.6.

So what to do? Well you can run in a part open loop, part closed loop configuration. You can set the AFR tables to something more appropriate (richer) for power bands etc. and leave it at 14.6 were you can get away with a leaner AFR. In fact the stock map already does this to an extent. At the extremes (0% throttle, WOT, RPM above 5000) the AFR's in the stock map are set to a much richer setting (13.0 to 12.5), and with these settings - something other than 14.6 - it's running open loop in those regions.

But what if other areas of the AFR table should be set to something other than 14.6 (and they should be)? Well you then have to increase the operating band that you will be running in open loop. Problem is, how do you know that any particular set point in your AFR table is being achieved (after all there will be no feedback)? This is were tuning your Volumetric Efficiency (VE) tables come in. For simplicity sake, think of the VE tables as a model of your engines "air" component in the Air to Fuel Ratio calculation. If those VE numbers in the VE tables are an accurate model for your engine, then you can be reasonably assured (notice that I didn't say absolutely) that you are achieving the desired AFR being set. So with accurate VE tables, you can expand the range in your AFR table that is operating in open loop, leaving the 14.6 switched closed loop ranges to areas where you can get away with it (idle, cruising under little load, etc.). Powervision Autotune Basic, Autotune Pro (with wideband O2 sensors), and Autotune with Target Tune (also with wideband O2 sensors), can be used to tune the VE tables. You will have to come up with an appropriate AFR/spark tables via other means.

So, if I greatly expand the area of the AFR tables to something other than 14.6, necessarily running in open loop, then why bother having any area set at 14.6 (running in closed loop)? Is there any area in the AFR table where it's really ideal to run at 14.6? Opinions may vary, but there are no cells in my current AFR table set to 14.6. So therefore - if I still had narrowband sensors - the bike would be running in open loop all the time (not using the sensors at all). Many people choose to run custom maps that don't have any cells set to 14.6, so they simply just eliminate the O2 sensors. If they have well tuned VE tables and appropriately set AFR tables, they can certainly get away with this setup and live happily ever after.

Personally, I run with a Target Tune and wideband O2 sensors. In my view, it's the best of both worlds so to speak. I have full time closed loop operation and have a custom AFR table that is appropriate for the bike. Closed loop with widebands allows the system to compensate for whatever conditions you may be riding in (changes in altitude, whatever). If there was no Target Tune, or similar option, then I would probably also eliminate the O2 sensors so that I can run with a more appropriate AFR table.

 

could you just alter the enrichment table and have the best of both worlds... power when you romp on it and gas mileage when criusing