My car has header with downpipe without CAT, so best thing is to install after 2nd O2.

 

i think you are giving wrong information here, the difference of flow in the two O2 sensors would not throw a CEL. how do you think people run test pipes without getting a CEL? most use nonfoulers, which moves the second O2 sensor out of the exhaust stream (less flow), thus fools the engine to think that there is still a Catalytic converter and it's working properly. that is all the second O2 sensor does. If you install a cut out in between the sensors that would be ok also because you wouldn't be driving around town with the cut out open, that would cause the CEL to come on, but if you had it open for a minute or two that would be just fine

 

good deal!

 

Not true ..... the ECU has parameters for balanced flow between the two O-2 sensors. If the primary has X amount of flow the secondary must be within a certain percentage of that % of flow. If not there will be a MIL. The Fit system is so sensitive that simply changing a header will cause a MIL.

When using a MIL eliminator you are correct that you are moving the sensor out of some of the flow to get the two sensor readings back into the parameters of the ECU. However diverting a large percentage of the flow from the secondary O-2 sensor by using an exhaust cut out is a different matter. The much larger percentage of difference between the two sensors will cause a MIL.

You are correct in your description of the working of the secondary O-2 sensor in that it monitors the operation of the catalytic converter only. That is the reason you get a MIL if there is a significant difference between the two O-2 sensors flow readings. If the secondary O-2 sensor detects a LARGE difference in flow caused by opening an exhaust cut out you will get a MIL because the ECU will interpret the difference in flow is because the converter is plugged and that is what is causing the reduced flow because it doesn't know there is an exhaust cut out installed on the vehicle no matter how long the cut out is open for.

If you refer to your Honda repair manual you will find that a clogged or partially clogged catalytic converter is indeed a valid MIL fault code.

 

You are somewhat correct.

a primary does not measure any "flow" as in air volume. it measures oxygen content, as per Honda manual. This then feedbacks to the ECU. There is no "balance flow" between the sensors (in respect to air volume). Primary measures oxygen content for a/f adjustment purposes. Secondary measures oxygen content after the reaction with the catalyst, sending feedback to the ECU whether or not the cat is still in working condition.

In vehicles with OBD2, a secondary sensor is fitted after the catalytic converter to monitor the o2 levels. The ECU then makes comparisons to the readings of the two sensors. If both sensors give the same output (same oxygen levels), it will code for the catalytic converter is non-functioning, and must be replaced. You can do your research on how a 3-way catalyst system works and the sensors to go along with it. What do you say that code for a "clogged" cat is? Whats the exact code?

It does not, however, measure air volume as you seem to state. So as long as the secondary sees less o2 than the primary, it believes that your cat is still functioning, no matter how less the air volume. ie. defouler method takes the secondary out of the exhaust stream (less air volume, and less o2 content), everything still runs fine with no codes. This method is done on MANY OBD2 cars and have a huge success rate in preventing a code thrown from the secondary. So in no way does the sensors measure and perform a balancing act with air flow. If that were the case, adding an aftermarket exhaust alone would throw a code b/c air flow is increased with a bigger diameter setup.

And still, even if the secondary throws a code, it will in NO way, affect performance as you stated. Stop worry about ppl throwing codes for the secondary. People who often eliminate the cat or plan on messing further upstream of the exhaust system know the risks of CEL/MIL lights coming on. Heck, many people run with it on. Although its not good practice to, its no problem as long as you keep a regular check that no other codes are present.

 

im no expert or anything, but i do know enough to know that there is no such thing as a "balanced flow" between the two O2 sensors. what i've always known was the first one measures air to fuel ratio then compensates. the second one measures the "quality" of air after the cat "cleans" it. if it's bad polluting air it throws a code, if it's clean air then no code. they work pretty much the same way, but independent of each other. so if one uses a a cut out, as long as the second O2 does not detect "dirty,polluting" air then will NOT throw a code no matter how much of a difference in flow there is between the two sensors.
i just looked over the P code list again and i see no "clogged cat" as a code . i understand a clogged cat can cause it to throw a code but i don't think there is anyway an O2 sensor can tell you if there is a clogged cat or not.

 

HUH you just proved my point

Ok here we go again discussing a moot point as Kimo has decided what he wants to do.

But anyway pull up a chair here is the lesson again in simple English.

Both sensors monitor the OXYGEN content of the spent exhaust gases (that's why they are called O-2 sensors) FLOWING past them, no flow no readings. If there is no FLOW of exhaust gases there is no correct reading.

During normal operation of the two sensors they both sample the flowing exhaust gases for OXYGEN content and the primary then relays this information to the ECU for a variety of uses and the secondary sensor JUST monitors oxygen content to insure normal catalytic converter operation.

During normal operation lets say the primary measures X percentage of oxygen remaining in the spent exhaust FLOWING past the sensor head.

This same exhaust flow then passes through the catalytic converter where the catalytic action changes the percent of oxygen remaining and the secondary sensor then reports Y percentage of oxygen remaining in the gas that flowed past it's sampling head.

Notice the amounts of oxygen measured IS NOT THE SAME but that is NORMAL operation. The ECUs parameters allow for and expect these readings to be different that is normal and that is "the balance between the readings".

Now if the primary reading is a normal X percentage of remaining oxygen but for some reason ..... lets say someone opens an exhaust cut out between the two sensors Z (a large amount LOWER ) not Y as normal, the ECU will see the NOT NORMAL DIFFERENCE between what is standard operating values but an abnormal amount of difference and see that as a malfunction of the converter and cause a MIL. Not dirty yucky air but the difference in remaining OXYGEN content as reported by the two sensors in the spent exhaust gasses FLOWING past the sensors.

 

I have change and the resonator, so the flow is much than before (stock) until the last muffler.

 

You are still wrong. Quang means if a clogged cat throws a code, it does not specifically mean its clogged. It could be clogged and still running fine with no codes, as long as the secondary o2 sees what it wants to see: lesser o2 content. You could hang the secondary o2 out of the exhaust flow completely and it will not throw a code for about 20miles. Readiness codes are not set right away so it takes time for it to realize that its not plugged into the cat.

Again, what is that magical code that says "Cat clogged"? You wont find it.

The sensors DO NOT measure air/o2 flow VOLUME as you say it does. Its not possible in the way the sensor is designed. If it wanted to measure FLOW volume, it would be something like a MAP/MAF sensor, which is placed before the engine. So a drastic change in flow in between the sensors will NOT throw a code. I guess u have no experience in this field to know. If what you say is true, you have still yet to show why defoulers/nonfoulers work so well. B/c it obviously takes it out from the exhaust flow.

Believe me, i've made up my own electronic o2 simulators for the secondary for myself. If anyone's worried about the secondary o2 throwing a code or the defouler method did not work, you can buy the electronic o2 simulator for a fair price. It basically goes in between the secondary's o2 electrical connector, works for all make/models.

Again, you lead this topic astray with almost-true, but still false information.

 

yeah i wasnt trying to be technical bro, the catalytic converter reduces pollutants (what i like to call "dirty" air) and no need to explain how a Cat works to me, im a bio major and in my Chem class we had to learn how it works down to the reactions it goes through, in the different stages of the cat converter.
you are just beating around the bush about the clogged cat code plus, is there a site where i can learn about the "balance in the 2 sensors." i want to learn more about it.
one more thing, correct me if im wrong but the computer doesn't even read the O2 sensors at WOT.

 

"The sensors DO NOT measure air/o2 flow VOLUME as you say it does."


I said they measure the percent of remaining oxygen in the gasses flowing past the sensor go back and read the post.

"During normal operation of the two sensors they both sample the flowing exhaust gases for OXYGEN content and the primary then relays this information to the ECU for a variety of uses and the secondary sensor JUST monitors oxygen content to insure normal catalytic converter operation." post #47

 

Easy peasy if you know how to use the manual..... Now that I did the work for you enjoy some light reading...

DTC Troubleshooting: P0420 (67-1)

DTC P0420 (67-1): Catalytic System Efficiency Below Threshold

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then recheck for DTC P0420.



P0137, P0138: Secondary Heated Oxygen Sensor ( secondary HO2S) (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
1.Reset the ECM/PCM, then continue to 2 through 5 to reset the readiness code.

2.Start the engine. Hold the engine at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on.

3.Drive for about 10 minutes without stopping on a highway or freeway. Your speed can vary.

4.With the transmission in 4th gear, drive at a steady speed between 80-100 km/h (50-62 mph) for 30 seconds.

5.Repeat step 4 three times. Between each repetition, close the throttle completely for 1-2 seconds. If the engine is stopped during this part of the procedure, go to 3 and do the procedure again.

6.Check for a Temporary DTC with the scan tool.
Does the scan tool indicate Temporary DTC P0420?

YES - Check the TWC. If necessary, replace the TWC.n

 

Wow all that just to install the cut open

 

P0420-meaning your cat is below efficiency; meaning primary and secondary both read close to the same amount of o2 levels. "low efficiency" meaning its not doing its job of catalyzing, ie. hole in honeycomb b/c excess burning of the catalyst. NOT b/c its "clogged". Like i said, it can be partially clogged, but still be efficient, but you have other problems to worry about if its clogged at all. If/when a cat is totally clogged, your car wont run for long due to excess backpressure.

P0141-happens when u dont plug in your o2 sensor to the connector (or loose/cut wiring) or if the sensor is defective and not activating the internal heater.

Thanks for proving my point. Easy peasy if u know how OBD2 works. Please do your research.

And no, you do not have to go thru the readiness process. Its for emission testing purposes if u're about to go thru the OBD2 test and recently reseted ECU. (ie. taking off battery terminal, etc) The ECU will automatically set the readiness codes to "Ready" status if u drive around for a while. You only need to do the above procedure for emissions testing. You can disable the whole OBD2 system and your car will still run fine.

Claymore, you stated they measured o2 flow as if u meant in volume.
-WRONG and there is abosolutely NO WAY anyone here can clog a catalytic converter without running leaded gasoline or running a HUGE amount of fuel additives. So get the idea of "clogging" out of your head and this thread. The sensors do not look for a "difference in flow" b/c there is ALWAYS a difference. Air before the primary moves faster than after the cat and secondary o2, so theres your difference in flow already.

Please clarify your definition of "flow" b.c i keep thinking that you're calling it "total air volume" instead of o2 content. And i think i'm starting to sound hostile again.

But in the end, a MIL is nothing to worry about if its from the secondary. Cutouts are pretty much only beneficial to USDM models, or if the non USDM relocate the primary sensor further upstream as claymore stated. May sound like a lota work but it really isnt. Just have your local muffler shop do it all. They know how to deal with the stuff on a daily basis. A good substitute is just to get a testpipe

 

Keep looking there are several more codes this one is just an example of one for reduced efficiency.

Like I said in the more technical post ""During normal operation of the two sensors they both sample the flowing exhaust gases for OXYGEN content and the primary then relays this information to the ECU for a variety of uses and the secondary sensor JUST monitors oxygen content to insure normal catalytic converter operation." post #47

Like I said in post #49 Notice the amounts of oxygen measured IS NOT THE SAME but that is NORMAL operation. The ECUs parameters allow for and expect these readings to be different that is normal and that is "the balance between the readings".


But anyway my recommendation is that if someone wants to install an exhaust cutout that works and does not cause a MIL just disconnect the standard exhaust system AFTER the secondary O-2 sensor. Get two pieces of straight pipe the same diameter as your exhaust system about a foot long.

Make one pipe end into a flange and mount one section of pipe so it is going straight out the back of the converter in the stock pipe location taking into account the lenght of pipe you need leaving room to mount the second pipe to the side.

Mount your exhaust cut out on the end of this new pipe so that if you open the cut out and look into the pipe you should be looking directly into the converter. Mounted this way is much more efficient than just slapping one on the side of the pipe so the flow has to make a 90 degree turn to exit.

Then take the other piece of pipe and angle cut it so it is pointing toward the rear of the vehicle as close to the cut out and original path of the exhaust as you can get it. Mark and cut a hole in the side of the first new pipe and weld the second new piece onto the side of the first pipe. Then bend and match the old exhaust pipe and connect them together.

Trouble free operation without MILS and having to reset your ECU. Open it when ever you want but be warned it is going to be LOUD.

Others may disagree so take your pick but the amount of power loss to the converter will be minimal if you mount it past the secondary O-2 sensor you will have MIL free operation, and still be legal ( as long as the cut out is closed) not like if you give up and mount a test pipe.

 

In that picture it also show that few gass can still flow to the muffler.

 

If you can draw it will be nice.