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Old 02-03-2011, 06:10 AM   #11 (permalink)
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Rich exhaust causes oxygen to flow from outside into the exhaust stream, and lean exhaust causes this flow to slow or even stop.
What? (can you draw a picture?)

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Old 02-03-2011, 06:33 AM   #12 (permalink)
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That's how an O2 sensor works. It works off of the diffusion of oxygen from one side of the sensor to the other. If there is a condition where extra oxygen is demanded and there is none present in the exhaust stream (such as for a rich mixture), oxygen flows from the air outside of the sensor into the exhaust stream. If there's an excess of oxygen in the exhaust stream, that flow slows down, or stops. Higher oxygen diffusion rates cause higher voltages to be generated by the O2 sensor, up to a point.

We're talking about minuscule amounts of oxygen, though.
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Old 02-03-2011, 01:54 PM   #13 (permalink)
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t vago -

Do you mean the outside air is "diffusing" through the membrane (shown below)? :

Oxygen sensor - Wikipedia, the free encyclopedia

Quote:
Zirconia sensor
The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere. An output voltage of 0.2 V (200 mV) DC represents a "lean mixture" of fuel and oxygen, where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). An output voltage of 0.8 V (800 mV) DC represents a "rich mixture", one which is high in unburned fuel and low in remaining oxygen. The ideal setpoint is approximately 0.45 V (450 mV) DC. This is where the quantities of air and fuel are in the optimum ratio, which is ~0.5% lean of the stoichiometric point, such that the exhaust output contains minimal carbon monoxide.
The voltage produced by the sensor is nonlinear with respect to oxygen concentration. The sensor is most sensitive near the stoichiometric point and less sensitive when either very lean or very rich.
The engine control unit (ECU) is a control system that uses feedback from the sensor to adjust the fuel/air mixture. As in all control systems, the time constant of the sensor is important; the ability of the ECU to control the fuel-air-ratio depends upon the response time of the sensor. An aging or fouled sensor tends to have a slower response time, which can degrade system performance. The shorter the time period, the higher the so-called "cross count" and the more responsive the system.
The zirconia sensor is of the "narrow band" type, referring to the narrow range of fuel/air ratios to which it responds.

Quote:
Wideband zirconia sensor
A variation on the zirconia sensor, called the "wideband" sensor, was introduced by Robert Bosch in 1994, and has been used on a lot of cars in order to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance at the same time. It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas pump current to keep the output of the electrochemical cell constant, so that the pump current directly indicates the oxygen content of the exhaust gas. This sensor eliminates the lean-rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry this sensor is also called a UEGO (for Universal Exhaust Gas Oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air-fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems, and can now also be used in diesel engines to satisfy the forthcoming EURO and ULEV emission limits.
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Old 02-03-2011, 11:23 PM   #14 (permalink)
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02 sensors detect combustibles not 02

the "wide band AFR sensors" do cycle
like an 02 sensor

you can not measure it with a low resolution scan tool but i have graphed and logged AFR sensors cycling rapidly
when they stop cycling

they are deader than dog poop , as they are used on newer systems , the system will set a DTC ... well before you need to start checking
unless they loose the zero and start misreporting actual conditions

monitor LTFT and watch for LTFT and STFT to be on opposite sides of zero by upwards of 10 percent
of course
a misreporting rear 02 sensor or an exhaust leak near either the AFR sensor or rear 02 sensor can send fuel trims to opposite extremes.

yes
newer systems with AFR sensor DO trim on the rear 02 sensor as well as the front AFR sensor


alternately
if you are using a HIGH RESOLUTION scan tool with a FAST update rate
you can graph STFT , tighten up the upper and lower limits to bracket the range of cycling
since STFT responds to inputs from the AFR sensor , graphing STFT is almost as good and will show if the AFR sensor flat lines

you can also look at
MODE 6 for system testing to monitor AFR sensor condition s like range and response time and heater condition

if you do not have a hi res scope and a hi res scan tool for your system
best to not be tampering with this


Last edited by mwebb; 02-03-2011 at 11:29 PM.. Reason: AFR trim R02 trim
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Old 01-03-2013, 09:56 PM   #15 (permalink)
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Quote:
Originally Posted by t vago View Post
Now, my question is - If an EFIE device is supposed to trick the engine computer into running leaner than before, by modifying the O2 sensor signal to make it appear that the engine's running more richly than it really is, how can you maintain control of the air fuel mixture if the O2 sensor output only goes to 15:1? Because it seems to me that if you're going to go beyond 15:1 (where real fuel economy gains would be realized), you're going to need something other than a device that merely changes the signal coming from a sensor that is limited to 15:1 on the lean end. Otherwise, you have no idea what the AFR is, and you'll eventually end up burning something up inside the engine due to an unanticipated over-lean condition.
I read that an EFIE adds a bit of voltage to the O2 sensor signal (like 0.2v for example), to basically skew the median to a leaner value. I agree, just installing this gizmo, dialing in a guesstimate voltage, and not having something to accurately monitor the result is not a good idea. However, I expect that is what several people do...and will be surprised when something goes ka-boom.
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Old 01-03-2013, 11:50 PM   #16 (permalink)
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Well, I've been thinking, on and off, of using a WBO2 controller to control a WBO2 sensor, and passing the output through a microcontroller to generate a simulated narrowband O2 signal for the stock engine computer. The circuit would modify the WBO2 signal as required, taking throttle position and MAP into consideration, to fool the engine computer into running lean.

After thinking and thinking about it, I've come to the conclusion that I well and truly hate this idea. Why? Because decent off-the-shelf WBO2 controllers cost at least $150 apiece, and I'd need to install 4 of them into the Magnum (2 pre-cat and 2 post-cat). That's on top of the 4 each WBO2 sensors themselves, which I think are about $50 a pop. That's at least $800, all told.

Alternately, to test the WBO2-controller-as-EFIE idea, I could go install my other ancient PLX WBO2 controller into the truck (for the post-cat O2 sensor), but... why? I don't drive it that much any more.
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Old 01-04-2013, 01:25 AM   #17 (permalink)
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the AFR "cycles" for two very important reasons....

#1 being that it's how the narrowband sensors are used to correct for fueling. if the sensor is constantly sitting near any one value, it's indicating that the sensing element is dead, it's not up to operating temperature or an extremely rich or lean condition is present. by forcing the AFR to "swing" around stoich, the ECM will cause the AFR to average stoich by attempting to make the time above and below the reference voltage equal.

#2 is the cat itself... supposedly they operate more efficiently when they are put into situations of slighty rich followed by slightly lean.... i really don't understand why, but it's been suggested that it needs some extra oxygen inside it to help the reactions. if this were the case, an AIR system that pumps air into the cat nearly all of the time would probably work quite well. or at least get it hot and keep it that way very quickly, though it wouldn't hurt to estimate cat temp so not to overheat it.
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Old 01-04-2013, 02:13 AM   #18 (permalink)
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Quote:
Originally Posted by RobertISaar View Post
#2 is the cat itself... supposedly they operate more efficiently when they are put into situations of slighty rich followed by slightly lean.... i really don't understand why, but it's been suggested that it needs some extra oxygen inside it to help the reactions. if this were the case, an AIR system that pumps air into the cat nearly all of the time would probably work quite well. or at least get it hot and keep it that way very quickly, though it wouldn't hurt to estimate cat temp so not to overheat it.
This is primarily why modern engine computers have AFR swing around stoich as you described. It's to get rid of air injector pumps that would be driven as an engine accessory - one less drain off the engine's output. The extra oxygen is pumped into the cat substrate during a lean cycle, and is then used to reduce the slight amounts of NOx and CO in the exhaust stream. This stored oxygen does not normally get depleted under normal operating conditions, but will get depleted when AFR goes rich (as with hard acceleration).
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Old 01-07-2013, 11:28 PM   #19 (permalink)
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Quote:
Originally Posted by t vago View Post
Well, I've been thinking, on and off, of using a WBO2 controller to control a WBO2 sensor, and passing the output through a microcontroller to generate a simulated narrowband O2 signal for the stock engine computer. The circuit would modify the WBO2 signal as required, taking throttle position and MAP into consideration, to fool the engine computer into running lean.

After thinking and thinking about it, I've come to the conclusion that I well and truly hate this idea. Why? Because decent off-the-shelf WBO2 controllers cost at least $150 apiece, and I'd need to install 4 of them into the Magnum (2 pre-cat and 2 post-cat). That's on top of the 4 each WBO2 sensors themselves, which I think are about $50 a pop. That's at least $800, all told.

Alternately, to test the WBO2-controller-as-EFIE idea, I could go install my other ancient PLX WBO2 controller into the truck (for the post-cat O2 sensor), but... why? I don't drive it that much any more.
I did find the Zeitronix ZT-2 has a wideband O2 sensor that has an adjustable narrowband output. So you could skew it lean as you like. But as you indicated, with a Dodge V8 you'd need at least two for the pre-cats. I asked Zeitronix and that's what they told me. Said I might throw a code from the post-cat O2s when running leaner. The truck doesn't get inspections (OK licensed) so that wouldn't be an issue, just annoying. At $300 each, I am inclined to just bite the bullet and blow my money on other things...like a lighter dampner or lighter wheels or something.
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Old 12-14-2013, 12:54 PM   #20 (permalink)
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Dust, dust... *cough* *cough*

I found this interesting thing... It's an open-source wideband O2 sensor controller, which uses an AtMega8 as the brains. They even provided the source code! Provisions for heater circuit and Nernst cell PID controllers are provided, as well as input signal processing and narrowband output simulation.

I may be able to adapt this controller to control 4 different WBO2 sensors. If this is possible, then I may be able to fool my Magnum's engine computer into going to 16:1 AFR for cruising.

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