Downstream O2 values

Hello group,

I'd like to ask you what post cat O2 readings do you consider a normal, good reading. Do you see any differences between manufacturers? (for example x brand typically hovers around 0.7v while z brand settles at 0.3v)

Do you see relevant differences between idle and higher rpm, given the engine is at normal operating temperature in both scenarios?

Thank you!

I generally agree that .7V tends to be the norm for a healthy cat and a functioning fuel control system. .6 - .8V is the rule-of-thumb I've run with for awhile, and it seems to work well.

Nissan is sometimes an exception, in my experience. They're not always running the downstream heaters when you're expecting them to. That can mislead you to see a lean downstream sensor, when really the sensor just isn't warmed up. They also like using some pretty intrusive O2/cat tests that can throw you for a loop if you don't understand what's happening.

If you are an Escan user, Bernie has a catalyst efficiency test built into the tool.

BUT......if you can get the generic O2 data, to perform Bernie's Cat Efficiency test is as follows:

1.Warm up Cats

2.Obtain Max/Min Voltages for S1 and S2 @ 2500 RPM Hot Engine

EG: B1S1 Max = .905v, Min = .07v, Max minus Min is 0.835v
B1S2 Max = .705v, Min = .02v Max minus Min is 0.685v

1 - (0.835v minus 0.685v) X 100 = 85% efficiency.

This formula has been obtained from Bernie's patent which is available online.

As Tyler stated it makes good sense to use his rule of thumb, because 0.6-0.9v on an S2 is a healthy cat.

And there is an exception to every rule because Nissan designed a cat with nearly half of the precious metals of a conventional cat!!!!

"Nissan has developed a catalytic converter that uses roughly half the amount of precious metals current models use. The catalytic converter is an exhaust chamber that is filled with a mix of platinum, rhodium and palladium. It captures harmful toxins in a car's exhaust such as nitrogen oxide, carbon monoxide and hydrocarbons by triggering a chemical reaction. Engineers at Nissan developed a technique that prevents the gathering of the precious metals in the catalyst under high temperatures. The result is that less of the metals are needed. The benefit to Nissan is a tremendous cost savings." - Wired.

So it would make sense the voltages are lower with Nissan on S2, thanks Tyler I did not know this!!!!!

Cheers

Paul P. wrote:

If you are an Escan user, Bernie has a catalyst efficiency test built into the tool.

BUT......if you can get the generic O2 data, to perform Bernie's Cat Efficiency test is as follows:

1.Warm up Cats

2.Obtain Max/Min Voltages for S1 and S2 @ 2500 RPM Hot Engine

EG: B1S1 Max = .905v, Min = .07v, Max minus Min is 0.835v
B1S2 Max = .705v, Min = .02v Max minus Min is 0.685v

1 - (0.835v minus 0.685v) X 100 = 85% efficiency.

This formula has been obtained from Bernie's patent which is available online.


Cheers

I am not sure to understand the logic of this efficiency calculation though. A not working cat where S2 follows S1 would result in 0 difference, indicating 0% efficiency loss, hence poining to 100% efficiency??

, I come up with a delta of 0,989 V for S1

S1 Max = 0.905v
S1 MIN = 0.07V

Max minus min 0.905-0.07=0.835V

and delta = 0,703 V for S2

S2 Max = 0.705v
S2 Min = 0.02v

Max minus min 0.705-0.02=0.685v

Now one step at a time;

0.835v - 0.685v = 0.15

and 1 - .15 = 0.85

and 0.85 times 100 Equals 85 %

I am not sure to understand the logic of this efficiency calculation though.

Here is the Link to Bernies Patent;

patents.google.com/patent/US8280578B1/en

I wonder how the Escan would fair out on a Nissan Cat like Tyler mentions. I certainly didn't dream this up!!!!!
But maybe Bernie has a much better understanding of how the OE's have to program the tests for Mode #6 using the O2 sensor voltages, and maybe now even temps are included in the calculation.

If you took the time to read the patent I also you Bernies formulas in Excel for Theoretical airflow calculations, they are for the most part "Bang-On" for MAF and Speed density systems ( with a speed density you will compare theoretical aitflow to the vehicles ABS loading values)

Sorry to leave you feeling confused.

Cheers

Thanks for your response. I noticed my fault for the delta values and edited my post before your reply was published.....

Nevertheless with regards to the formula:

A downstream sensor with the same swing as the up stream sensor would result in delta S1 - delta S2 =0, then 1-0=1, equaling 100%??

I'll have a look at the link you shared, thank you.

A downstream sensor with the same swing as the up stream sensor would result in delta S1 - delta S2 =0, then 1-0=1, equaling 100%??

Sure it would, but at that point there isn't any catalyst efficiency is there. Im certain Bernies tool "knows" this.

I doubt it would run a CAT Efficiency test with an oscillating post O2.

Cheers

Paul P. wrote:

Sure it would, but at that point there isn't any catalyst efficiency is there. Im certain Bernies tool "knows" this.

Cheers

Indeed,there would be no efficiency. And that is what it makes hard to follow the approach.

Independently from absolute values and logic thresholds
that may or may no be programmed into the tool's software:what stands out with the given formula is the tendency to report higher efficiency the closer pre and post O2 sensor readings are to each other. This just seems to be "the other way around".