for the guys that wanted the technical on O2 Sensors...

[HiTechRedNeck73]

How they work -Simplified
Titania sensors do NOT have the ability to produce a self-voltage. Instead, the engine ECU supplies a base reference voltage. If the air/fuel ratio is rich, the resistance in the sensor is low. When the fuel mixture is lean, resistance in the sensor is high. The ECU then uses this high or low signal to adjusts the fuel flow through the fuel injectors. The speed with which it can change from reading a rich to lean or lean to rich air/fuel mixture is called its cross count. The higher or faster the cross counts, the better the sensor.

How they work –Simple details
Your engine will produce the greatest power and the fewest emissions when the air/fuel mixture is kept at a ratio of 14.7 to 1. This is referred to as “stoichiometric”. To try to keep the air/fuel mixture at this ratio, the ECU sends a base or reference voltage to power the titania sensor. It then looks for the signal back from the sensor which will be measured by the amount of resistance ranging from a low resistance of 1000 ohms (when the engine air/fuel mixture is too rich) to a high resistance of over 20,000 ohms (when the air/fuel ratio is considered too lean). The ECU reads the resistance voltage being reported from the sensor and makes adjustments to the fuel through the fuel injectors accordingly. Unlike the newer zirconia sensor, the titania sensor does not require outside reference air to do its job, it is a sealed environment sensor

ok, so here is a wiring schematic of what your typical 4-wire sensor does...
http://www.supermotors.net/getfile/672743/fullsize/423.jpg

here is the closeup of the eletro-chemical schematic...
http://www.supermotors.net/getfile/672741/fullsize/306.jpg

here is what it sends back to the ECM (engine computer)...
http://www.supermotors.net/getfile/672740/fullsize/305.jpg

here is what it all looks like to us...
http://www.supermotors.net/getfile/672739/fullsize/304.jpg

basically, it measures the resistance across the ions of oxygen that make it into the sensor, and then uses that resistance to return a voltage (from the ECU reference voltage) back to the ECU for processing... the ECU looks the voltage up in the fuel table, and thinks it knows how much air and fuel went into the engine in the first place... then it adjusts accordingly....

[donnylynn]

Thanks for the explanation. Now a question.
How do the O2 extenders change the O2 sensor reading to make the ecu think it is running rich?

[HiTechRedNeck73]

Thanks for the explanation. Now a question.
How do the O2 extenders change the O2 sensor reading to make the ecu think it is running rich?

it doesn't make the o2 sensor read rich... it moves the sensor out of the exhaust stream and reduces the amount of exhaust (and o2) that reaches the sensor...

but, this doesn't work on all vehicles... for example, my car is a 2004 Dodge Intrepid SE 2.7L v6... my car has three cats, a muffler and a resonator... with all that on the pipe, there is a certain amount of back pressure created in the exhaust pipe... that would circulate the exhaust gases and reach the o2 sensor anyway... so I don't see where those would work on my car... they might work if I gutted the cats, and removed the resonator (not required for emissions, it's there to quiet the exhaust noise)... I could also reduce back pressure by installing bigger pipes, going from 2.25 to 2.5 or go to true dual exhaust...

now here is another issue... I wonder if there is truly more oxygen in the exhaust stream, or is the sensor being fooled from the beginning... based on the way it uses the resistance of the o2 to give a reading back to the ECU, if there was too much electrolyte getting into the exhaust (through the engine) or the high content of water (in the form of steam)... both have a resistance... and I'm sure it's much lower than o2 by itself, which is what the sensor is expecting...

food for thought...

and all the more reason to have o2 adjustment on the electrical end in stead of extenders...

[donnylynn]

but even if it is moved out of the direct stream of exhaust flow, it is still exposed to the content of the flow. It is recessed back. I am assuming that the sensor is not vented in any way to allow outside air access to the tip. If that is the case, it may be seeing a slightly lower temperature by not being in the exhast flow and the extender is allowing the sensor tip to be slightly cooler. Perhaps the sensor has a temperature coefficient that is being affected????

[HiTechRedNeck73]

but even if it is moved out of the direct stream of exhaust flow, it is still exposed to the content of the flow. It is recessed back. I am assuming that the sensor is not vented in any way to allow outside air access to the tip. If that is the case, it may be seeing a slightly lower temperature by not being in the exhast flow and the extender is allowing the sensor tip to be slightly cooler. Perhaps the sensor has a temperature coefficient that is being affected????

I don't think there is a problem with temp in today's engines... if most are like mine, all 4 of my o2 sensors are within inches of the cats... that gives all the temp they need, IMO... in fact, coming to mind is the procedure for checking o2 sensors... my factory service manual says to check the resistance across the heater and compare to a chart in the manual... it cautions to do this at room temp... so I have one sitting around and heat it up - it's out of spec... too much resistance... let it cool off - it's within spec... so there must be compensation for temp...

more info...

4-wire (90s tech) o2 sensors use a heater to heat up the reference air... 5-wire (latest tech) o2 sensors use an outside (ambient) temp sensor for reference...

the reference air is used to compare to... there is no telling what is in there... only the manufacturer knows... with as simple as an oxygen sensor is, I'd say the real reason for o2 sensors going bad is the expulsion of this reference air... it's the only thing that would make the whole device fail...