O2 Sensor question

[txoutlaw]

Are the pre cat and after cat O2 sensors really different or do they just come with different connectors and jack up the price at the dealeship?

[WS6FirebirdTA00]

what is this for? fbodys are interchangeable front and rear, just the wire length is different

[EC_Tune]

The sensors are constructed the same. Zirconium matrix.
Here's something I pulled down about them (not on the web anymore...)


Oxgen and Air-to Fuel Ratio Sensors for Automobile

1) Potentiometric Oxygen Sensor
Attachment 129
When a Pt/YSZ/Pt cell with a U-shape lies between the two different oxygen partial pressures, one can get the electromotive forces(Vmax) across the YSZ as follows:

• Vmax=(RT/4F)ln[Po2(air)/Po2(exh.)]

where R, T, F, Po2(air), and Po2(exh.) are gas constant, absolute temperature, Faraday constant, oxygen partial pressures at the air and exhaust gas, respectively. The e.m.f. of this sensor changes abruptly at the stoichiometric point. Therefore, this sensor has been widely used for the stoichiometric control of an automobile engine.

Related Links

• Oxygen Sensor Information by Rick Kirchhof
• NGK Oxygen Sensor
• Delphi Oxygen Sensor

2) Limiting Current-Type Oxygen Sensor
Attachment 130
The oxygen concentration of a gas can be determined by the limiting current of a electrochemical pumping cell witha diffusion barrier. This sensor is called as 'Limiting current-type oxygen sensor'. The figure shows the principle of this amperometric sensor. In the low voltage region, the oxygen pumping amount is less than the gas diffusion from the ambient toward the cathode.(region 1) However, the oxygen pumping amount is limited by the gas diffusion above the certain voltage.(region 2) This current is called as 'limiting current'(Ilim) and can be expressed as follows assuming the Knudsen type gas diffusion:

• Ilim=(4FDo2sP/RTl)Xo2

where Do2, s, P, l, and Xo2 are the diffusion coefficient of oxygen, the cross-sectional area of the pore, the pressure of the gas, the length of the pore and molar fraction of ambient oxygen, respectively. Therefore, one can get the limiting currents proportional to the oxygen concentrations.

Related Links

• Limiting Current Type Oxygen Sensor by Fujikura
• Amperometric Gas-Phase Sensor

3) Wide Range Air/Fuel Ratio Sensor
Attachment 131
The wide range air/fuel ratio sensor can be set up by combining the potentiometric and limting current sensors. The current of the pumping cell was controlled for getting the constant e.m.f.(generally about 450mV, that is, Po2 at cavity is about 10-10) at the sensing cell by feedback algorithm. In the fuel-lean region, the oxygen concentration at the ambient and cavity is relatively high. Therefore, the oxygen should be pumped from the cavity to the ambient to get Po2(cavity)=10-10. And the oxygen pumping amount increases with A/F ratio because the oxygen concentration is higher at the more lean A/F region. On the other hand, in the fuel region, the oxygen should be pumped toward the cavity. And the Po2=10-10 is attained by the oxidation reaction between the reducing gases at the cavity and oxygen pumped from 1 to 2. So the oxygen pumping amount increases with decreasing the A/F ratio because the more oxygen is needed in the oxidation reaction with the reducing gases(CO, H2, and CmHn) at the richer region. Therefore, the A/F ratio can be measures by the amount and direction of the oxygen pumping to get the constant e.m.f. across the sensing cell.
Related Links

• NGK Wide range A/F Sensor

[EC_Tune]

A new catalyst monitoring sensor
Attachment 132 The three-way catalyst has been successfully adopted to gasoline engine to reduce pollutant emission. The engine is generally operated at the stoichiometric air:fuel ratio (A:F, about 14.7) by using a lambda sensor in order to maximize the efficiency of catalytic conversion from CO, Cm Hn , and NOx into CO2 ,H2 O, and N2. It has been reported that the catalytic activity gradually decreases under the exposure to high temperature or chemical poisons such as lead or lubricant derived phosphorus. However, the catalyst degradation is hardly detectable unless a malfunction indicator is in-stalled. Therefore, the monitoring of catalyst degrada-tion is important in order to maintain low emissions of CO, HC, and NOx . Many researchers have studied the catalyst-monitor-ing algorithm. Typically, two A:F sensors were placed before and after the catalyst and their signals were compared in order to check the changes of A:F due to the catalytic reactions. A pair of lambda sensors or wide range A:F sensors have been suggested to be installed for this purpose.
The lambda sensor measures electromotive forces between the exhaust and the air across a stabilized zirconia tube. This potentiometric sensor shows an abrupt signal change at the stoichiometric point of A:F because the concentration of oxygen in the exhaust changes extensively around this point after the equili-bration of gas phase over the Pt catalyst attached to the sensor. This feature makes it easy for one to control the engine at the stoichiometric point. The cost of lambda sensor is fairly low owing to successful mass production and the sensor stability has also been confi-rmed. On such background, the two-lambda sensor method has been proposed to detect the deterioration of catalyst. However, limitation of this method has been pointed out: When the HC conversion efficiency goes down to less than 70%, both of the sensors pro-duce the similar sensor signals in the fuel-lean or the fuel-rich regimes leading only to a small difference of EMF in between.
The wide range A:F sensor consists of an oxygen pumping cell, a sensing cell, a gas diffusion barrier, and a feedback control circuit. The last one controls the direction and amount of oxygen pumping according to the electromotive forces of the sensing cell. This sensor can detect even a small A:F change within the fuel-lean or the fuel-rich regime because its signal is almost proportional to A:F. So the catalyst monitor using the sensors of this type can detect the degradation of HC conversion efficiency down to 40%. However, the sensor has been fabricated by stacking several layers of YSZ and other materials which are very different in property and/or structure from each other. It is not easy to co-fire the laminates due to the differences in shrinkage during sintering. Furthermore, the operating algorithm is not simple, needing a complex driving circuit.


Attachment 133 In this study, a new sensor based on the limiting current principle was designed to detect the catalyst degradation. Unlike conventional YSZ devices, the sensor utilized a layered porous composite of YSZ and Al2O3 , which could work as an oxide-ionic conductor as well as a gas diffusion barrier. The sensor was fabricated by stacking three layers of identical YSZ-Al2O3 composite with Pt electrodes being inserted in between. The stacking gave rise to an oxygen-pumping cell sandwiched between gas diffusion barriers, the limiting current of which was almost proportional to the concentration of O2 or CO in CO2 -containing atmosphere. Being easy to fabricate and simple in driving algorithm, the new sensor seems to fit well to the catalyst monitoring system. In this paper, the limiting current characteristics of the sensor were measured in CO-CO2-N2 atmosphere (fuel-rich condition) and O2-CO2-N2 (fuel-lean condition). Finally, the sensors were installed before and after the three-way catalyst in the exhaust line from a gasoline engine to confirm the applicability to the catalyst monitoring system.
Attachment 134Attachment 135

[txoutlaw]

My question was relating directly to cost!, the vette's have different connectors fr to rear so what i really was looking to do is save some people money simply by changing the connectors out if they are the same! the cost from the dealer is double for the rear!

which brings me to my next question what is the best route when working on hybrid cars (LSx in Whatever) with a stand alone harness and ECM. delete the S1 or S2 when dealing with using only one set of O2's.

[EC_Tune]

You can drop the S2's & turn `em off.

[jmoody66]

Emission controls question. I live in Texas and want all of my emissions systems to be on...HP gains are minimal and I dont think polluting our air is worth my smiles for some extra hp. The previous tuner turned everything off...I believe the COTand air pump. Well that didnt allow me to pass emissions due to several "not ready" status notices on the test station. So Im looking at my tune and see "EGR" disabled. Shouldnt this be enabled? Is there anything else that I can turn back on that would ensure ALL emission systems are active? Thanks

[AdubZ28]

Your car didn't come with EGR

[EC_Tune]

COT won't hurt you unless you truly overheat the cats. (WOT for 10 miles.... )
Do you have a stock cal as a go-by?

[anymanusa]

COT won't hurt you unless you truly overheat the cats. (WOT for 10 miles.... )
Do you have a stock cal as a go-by?

sometimes it only takes a few donuts in an empty parking lot... Much less than 10 miles worth.

[jmoody66]

COT won't hurt you unless you truly overheat the cats. (WOT for 10 miles.... )
Do you have a stock cal as a go-by?

There is no EGR..forgot that one.....I didnt have a stock tune to go by. I bought my car modded but the guy that sold it to me had already done some tuning on it therefore I have never seen the stock tune.
I dont think I took long enough to respond to this thread.....

[anymanusa]

COT won't hurt you unless you truly overheat the cats. (WOT for 10 miles.... )
Do you have a stock cal as a go-by?

uh, all it takes is a couple seconds worth of WOT donuts and they're toast.

Miles, and maybe your exhaust melts into a pile of molten steel.

[EC_Tune]

There is no EGR..forgot that one.....I didnt have a stock tune to go by. I bought my car modded but the guy that sold it to me had already done some tuning on it therefore I have never seen the stock tune.
I dont think I took long enough to respond to this thread.....

Heheh, You can probably find a stock file for comparisons purposes in the repository.