O2 Sensor

[BUCKET]

Isn't the O2 sensor supposed to tell the puter thingy to let the injection thingy know how much fuel to send to the combustion chamber thingy.so when we pput aftermarket pipes on why do we have to remap.A friend told me that there is 2 types of puters,open loop and closed loop circuit,i said huh.Please explain oh wise ones. :hammer:

[Gnome]

Just buy a Power Commander and lose the sensor all together, get it mapped by a dynojet tuner and book a weekly visit with your doc - to help remove the smile (aches after a while)

.GNOME.

[TrackerOldGuy]

Gnome's summary is correct. I am not a tech expert but basically the stock o2 sensor is narrow band which means
it only allows the stock map to make small adjustments to the not too good stock A/F ratio map. The dyno guys use a wide band sensor to do an accurate custom map for the TuneBoy/PowerCommander systems. Then the stock o2
sensor is permanently disconnected because the new
tune/program/map doesn't like it/need it. Also the dyno boys disconnect the Secondary Air Injection system during the custom tune so the wide band sensor doesn't get confused
by more air getting pushed by it upon occasion ( like deceleration---popping) thus you can remove the SAI system and put in block off plates if you want.

I am sure that you will get a better explanation from some other folks ( ps---when prefectly set up an electronic fuel injection system will run like a good carburetor----that should cause a fight ).

[JW69ers]

A good tuned fuel injection system will out perform a carb.

Tuneboy will still use O2 sensor. Power Commander needs to eliminate O2 sensor otherwise it will loose its (adjusting) function.

Ask Dr Gallup if the system is open or closed loop, he helped design it ... where are you Dr?

[BUCKET]

Interesting,very interesting,thanks people. :hammer:
Ps:Now my brain has to start thinking again,***** youse. :-D

[Avi8or]

Open loop=fuel injection with no feedback. All fuelling is according to the mapped memory.

Closed loop=fuel injection with feedback, ie the O2 sensor reads the actual mixture and then 'instructs' the injection system to apply the neccesary correction to supply the correct mixture.
In actual fact the only time the S3 works in closed loop mode is during light throttle and steady running conditions ie cruising. Seems that this is so 'cause the o2 sensor lags quite a bit and could be giving injectors wrong instructions, at the wrong time, potentially leaning off the mix, when rich is required. Bad news.

[dr_gallup]

Well, you're all part right. The S3 does use a narrow band O2 sensor, just like nearly every catalyst equiped car or motorcycle sold recently. The narrow band sensor only tells the computer if you have excess oxygen or not, ie rich or lean from stoichiometric air fuel ratio (~14.7). Stoichiometric A/F is necessary for the exhaust catalysts to work efficiently. Fortunately for all of us, the regulatory emmission tests are run using a driving cycle that only encompasses light throttle and moderate RPM, like ideling, driving around town (without the wheelies) and crusing on the highway. So that is the only part of the engine opperating range that is closed loop. The rest of the time, the engine goes open loop. The ECU just reads a lookup map and determines the fueling based on pre-programed values. This is where you need a wide band O2 sensor (or more advanced exhaust gas analysis). Typical best power A/F will be in the 12.5 to 12.0 range.

The Tuneboy lets you reprogram the lookup map. It also lets you change everything in the ECU programing including spark timing. The Power Commander just intercepts the ECU injector drive signals and adds or subtracts injector pulsewidth depending on the map that you put in it. It can only change fueling, nothing else.

PS I only designed the SAGEM injectors.

[Curmudgeon]

Great post, David!

[BUCKET]

So Dr,with this new stumpy can i have put on does the standard puter have enough in it to be re mapped to suit.From what i can gather it should be right at the levels you have suggested,highway,round town cruising,but not under fast accelerating.The pipe seems to have given it a lot more bottom end and doesn't seem to be leaning out up top.I designed these mid pipe so the standard O2 sensor could still be used so people didn't have to buy a aftermarket puter.Please explain again. :hammer:

[dr_gallup]

On 2006-09-11 12:43, BUCKET wrote:
So Dr,with this new stumpy can i have put on does the standard puter have enough in it to be re mapped to suit.From what i can gather it should be right at the levels you have suggested,highway,round town cruising,but not under fast accelerating.The pipe seems to have given it a lot more bottom end and doesn't seem to be leaning out up top.I designed these mid pipe so the standard O2 sensor could still be used so people didn't have to buy a aftermarket puter.Please explain again. :hammer:

Most people find that just downloading the TORS tune will work reasonably well with aftermarket exhausts. Certainly Trident & Zard, don't know what you have cooked up. Of course, if you want to optimize it then dyno time and a Tuneboy or PC is needed.

Derek - with the Tuneboy you can change the target A/F values and the ECU will totally ignore the O2 sensor, open loop all the time.

Most people do not have access to 4 gas analysers nor the ability to make sense of all the data. For the typical small town speed shop a wide band sensor and an inertia dyno are all that is available. You can still get pretty good results with that, much better than no data at all. The discrepancies between 4 gas EGA and wide band O2 sensor usually is a function of cylinder imbalance. The O2 sensor is always going to respond to the leanest cylinder since it is only reading O2. The other cylinders can still be stinking rich (high CO) but the O2 sensor will read lean if there is excess oxygen.