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Oxygen sensor

2579 Views 4 Replies 5 Participants Last post by  nightrob
I hope you will not mind my question, since I need your inputs in order to understand the difference between the EFI bikes' exhaust systems (and the work of ECMs, engines) with oxygen sensors, and the older-style EFI bikes' exhaust systems (and the work of ECMs, engines) with NO oxygen sensors.

OK, oxygen sensor needs to determine the AFR by analyzing exhaust gases. Then, utilizing input from the sensors, the ECM's adjust fuel delivery to maintain factory-set AFR.

So, if we have O2 sensor, why we still need a DFO/Power Commander/SERT etc when we install after market parts (slip ons and high flow air filter)?

We also need a DFO/Power Commander/SERT on the bikes with no oxygen sensor, but with after market parts (slip ons, air filter) added. This is OK.

How come that older EFI bikes did not need/have the oxygen sensors? Is this just an improvement over the bikes with no oxygen sensors in order to enable better ECM and engine response?...I still don't get it.

Thank you very much for your comments.
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I believe there is a service bulletin floating around somewhere that says you do not have to adjust the ECM when you add the standard Stage 1 (Air Cleaner, exhaust). Plus, many technicians have reported such in some Harley related publications.

However, keep in mind that ECM's fuel management is not unlimited. There is only a narrow band with which the ECM can adjust. (i.e. +/- x%) In addition, as AirGlider has mentioned, there are times in which the O2 sensors input is discarded and the fuel management system relies on an open FI map.

In my humble opinion - nothing beats a good tune, be it with a SERT/TTS, Powercommander, or one of the ECM replacement tools.
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