Are you running catalytic converters or not with boost?

[markmurfie]

One skilled in the art is capable of performing such experiments without further explanation.

A fore-aft oxygen sensor (FAOS) fuel control system. The control system uses an A/F bias for trimming the closed-loop operating point of a pre-catalyst A/F feedback controller. The A/F bias is generated by a proportional-integral feedback signal from a post-catalyst EGO sensor feedback controller fed by the output of a post-catalyst Exhaust Gas Oxygen (EGO) sensor.
A substantial time delay is associated with the post-catalyst feedback loop. Therefore, this control system is subject to some A/F errors. A/F errors result in catalyst breakthrough and higher emission levels, making it difficult to meet the stringent emission regulations.
In an attempt to improve the performance of the FAOS control system, it has been proposed to use a modelbased feedback controller. In the model-based system, the inputs to the system to be controlled are also applied to a model. The model is adaptively updated based upon a comparison between the output of the model and the output of the actual system. The output of the model is used to generate a real-time corrective signal to rapidly compensate for potential, or present, system response errors. The accuracy of the model is important to the success of the modelbased system.

FAOSC Rich excursion correction factor

FAOSC Lean excursion correction factor

The referred to figures these correction factors were derived from.

Im pretty sure disabling FAOSC just changes from using these or something very similar, to a constant oxidizing and reducing species for the A/F Bias. Nothing to do with correcting for the age of sensors, but likely monitoring the age of the catalyst and its storage capacity to throw one of those efficiency codes.

With out correction factor vs with correction factor post cat AFR model vs measured.

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[K4fxd]

Mark are you saying turning off FAOSC will not cause A/F drift?

 

[wingnutt]

Yep…gonna need a TLDR on that one

 

[WildHorse]

Mark are you saying turning off FAOSC will not cause A/F drift?

HAd to look it up. Boils down too catalytic process :

The model-based system uses the information from these sensors to ensure the catalytic converter is functioning properly and efficiently reducing harmful emissions. The accuracy of this model is important because it directly affects the system's ability to detect potential problems with the catalytic converter and maintain proper emissions control.
By comparing the readings from the fore and aft sensors, the system can determine how well the catalytic converter is performing. If the difference between the two readings is too large, it could indicate that the catalytic converter isn't working as efficiently as it should be, which would throw a code(s).

In plain English, this means that there's a system in place that uses a mathematical model to predict how a certain process will behave. As the system operates, it compares the actual behavior of the process to the predicted behavior from the model. If the model detects any errors or differences between the predicted and actual behavior, it quickly sends a signal to correct or adjust the processes actions.
The accuracy of the model is crucial because it helps ensure that the corrections being made are appropriate and effective. If the model is not accurate, the corrections might not be accurate either, leading to potential issues with the catalytic process ... In the event of system codes, the model will go to another table and disregard said process.

 

[K4fxd]

My question to Mark really is if we remove the cats and turn off the rear sensor will the system drift? If so can we keep the rear sensors and FAOSC? without cats

 

[WildHorse]

To put his first paragraph in another way :

The pre-catalyst sensor provides real-time feedback to adjust the fuel-to-air ratio to a desired level. The post-catalyst sensor checks if the catalytic converter is effectively reducing harmful emissions by comparing the difference in oxygen levels before and after the converter.
A computer model helps to improve the performance of this system. The model takes input from both oxygen sensors and predicts how well the catalytic converter is working. If there's a difference between what the model predicts and what's actually happening, the system adjusts the fuel-to-air ratio to reduce errors and maintain the best performance of the catalytic converter. The key to this model's success is its accuracy. If the model can accurately predict the system's behavior, it can help minimize errors and maintain optimal fuel-to-air ratios, which in turn helps to minimize harmful emissions from the vehicle.

It's self explanatory. O2's are gonna drift with age/deposits/etc., weather there's 1, 2, 4 or 10 o2's, the logic has no way of telling if the fore o2's are 'drifting' .

 

[K4fxd]

What I'm seeing is pulling the cats does not screw with the front wide band. The rear sensor is strictly for emissions and not WB calibration like has been told and re-told for years.

Looking at some other patents the rears do calibrate the fronts

 

[WildHorse]

Looking at some other patents the rears do calibrate the fronts

As said here: https://www.mustang6g.com/forums/th...-or-not-with-boost.206006/page-3#post-4131446

Calibrate for what purpose ? Emissions ? Speak or show a link.

 

[markmurfie]

What I'm seeing is pulling the cats does not screw with the front wide band. The rear sensor is strictly for emissions and not WB calibration like has been told and re-told for years.

Looking at some other patents the rears do calibrate the fronts

From a different patent:
"This invention includes using two exhaust gas oxygen sensors (HEGO), one located upstream of a catalyst and one downstream of the catalyst, wherein the downstream HEGO sensor provides a feedback signal for learning control of the air fuel control system. The HEGO bias term learns based on the rear HEGO voltage. The bias term is used in an air fuel ratio limit cycle (oscillation) control to shift the air fuel control to operate in a catalyst window. "

"Referring to fig 2. an air/fuel ratio feedback control system includes an A/F bias table which supplies, through a summer, a bias signal to an A/F feedback controller for changing the integrator gain of the proportional integral (PI) controller (A/F feedback controller) as a function of engine RPM and torque of the engine. The Bias signal corrects for the different operating characteristics of the front HEGO sensor at different engine RPMs and torque. Summer also receives a signal from a rear HEGO sensor feedback controller, which has the effect of modifying the bias table signal. This moves the table values up or down and is done primarily to correct for the aging of upstream HEGO sensor. "

This correction that people are are saying is FAOSC, is a sub routine and not a main part in the bias FAOSC uses. The specific state that FAOSC needs to be in and other criterias for this to be allowed is described in fig4 a thru i in this patent. With out cats, FAOSC goes into a ineffeciency state, and this sub routine is disabled. This sub routine isn't effecting fueling based on the all criteria needing to be meet. If defoulers (they dont work IMO and experience) are keeping the rear O2 from detecting this ineffecient state, the system would be working to figure out whats happening with the cat, It wouldnt be accurate enough for adjusting the front sensors.

Sensor responce slows down as they age, this compensates for that, and maintains an accurate rate for air fuel ratio limit cycle (oscillation) control.

FAOSC is described in the patent I was referencing in my previous post.

 

[robvas]

I was next to a 3V Mustang with cams and no cars today in traffic...sounded great but man did it stink. I don't miss that at all

 

[WildHorse]

@markmurfie nailed it, then nailed it again.

 

[ben1]

I happened upon this thread and though some of you may find the following test results useful in regards to the long term trimming of the forward O2 sensor by the rear. About a year ago I tested and confirmed this issue with multiple logs over the course of several weeks using a catless S550 with something very similar to defoulers for the rear sensors. With FAOSC turned OFF the fuel trims would stay very small +/-3% both immediately after a KAM reset and after several drive cycles. With FAOSC turned ON, right after a KAM reset the fuel trims would start off small but then they would gradually worsen after a few drive cycles to the point where they were over 10%.

 

[DougS550]

have seen a couple of people say no issue running cats and quite a few say it’s a time bomb if you don’t get rid of them.

trying to plan my stage 2 whipple build on what all I need to do when adding blower vs what can wait.

not opposed to running no cats due to no emission checks down here.

My state does not have EPA inspections, but I went on and got the high flow cats with my LTH headers.

 

[cbrtrx]

Lots of very smart answers here and quotes from patents almost 20 years old. If you remove the cats the rear O2s will no longer correctly adjust for FAOSC. I've been testing this for years on coyotes. Another issue some longtubes will have multiple slip connection points between the front and rear O2s which potentially could have leaks and cause even more discrepancy with FAOSC enabled. If you're very worried about drift replace the front O2s every year or so.

 

[markmurfie]

If you remove the catalytic converters, leave FAOSC enabled, the rear sensors will no longer have any delay in its responce to lean/ rich excursions compared to the front. The capacity of ox/ redox species in the catalytic converter will be assumed to be 0 and failed.

Think about this:
Whether the front sensors are a narrow band(as described in the second patent referenced and pictured below) or a wide band, the adjustment the rear sensors can make through its feedback loop will be the same bias voltage. The criteria of when this correction can be determined is different. This adjustment over the life of the front sensor and catalytic converter is very small, happen only in very rare conditions, and has limits imposed on it. All for extremely strict emissions control standards.

You dont need to replace your O2 sensors more often, as they will be detected bad via the normal methods. Removing the catalytic converter is not going to cause the sensor to wear out any slower or faster. When an O2 sensor deteriorates, the period of the cycle of O2 sensor output becomes longer. A/F deviates to the rich side. This is because the period from lean to rich is different from rich to lean. Hence the patent I first referenced explaining how to model the rear O2 differently for rich excursion and lean excursion in a FAOS fuel control system to make it a FAOSC model. Finally, from what the second patent references and what this minor correction is for. Under normal operations catalytic converters are expected to out live many HEGO sensors.

Ben:
You won't see + or - 10% over time in fuel trims. You won't see anything, but a trouble code. If the front sensor was drifting that much.... How would it tell you that in a log via fuel trims, but not say the sensor is bad being that inaccurate?
Take it from Bugasu, Eco boost tuning guru nearly 10 years ago, if not from me.

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