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What do you think the non-foulers are?????????????
 

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Interesting, never seen spark plug defoulers that used for that purpose. Did you try using one on the downstream O2 sensor only?
 

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Discussion Starter #23
Yes. I understand why the code is being thrown. =)

This is why I used non-foulers on the downstream O2 sensor. It backs the O2 sensor out of the path of the exhaust to throw off the reading enough to trick the ECU into thinking its functioning properly. This is the same trick and method that people have been using for years on other cars when they install long tube headers. It has worked for me on a few other cars I've owned. I don't understand why its not working on my focus though. Which makes me think it could possibly be something else.

I read another thread on here where a guy tried the same thing and it would not work. So he packed some steel wool into the nonfouler with the sensor and that did the trick. Sounds strange but I will try it when I am changing the alternator this weekend. It's almost like its needs even more blockage from the exhaust to trick it. IDK. If it doesn't work, I am getting the code disabled. I hate throwing parts at a car just to clear a code when it's operating perfectly fine.
 

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Had this on my escort. Check top of sparkplugs for trapped water. Trying to recall if I actually fixed it or just kept going in to emitions at 20miles when the computer set before the code came back.
 

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Discussion Starter #25
I replaced the alternator this weekend and that cleared up my intermittent battery light issue. So glad that's over with.

I did the steel wool trick and packed some into the non-fouler. 150 miles so far and no code. I am not out of the water yet. I will not be confident that it worked until 300-500 miles. I will report back if it comes back or not.
 

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Discussion Starter #26
Battery light has not come back since alternator change so I am pleased with that.

Check engine light came back on. So given that I have two non-foulers and steel wool in there, I can't imagine the cat is still causing this issue. I did some general searching online for that code and found a variety of things that can cause it like dirty TB, dirty MAF, too much or too little fuel pressure due to vacuum leak. I actually did clean the MAF over the weekend so I can rule that out. I honestly don't want to spend a ton of time on this car trying to track this down. Like I said before, it runs and drives great. I filled up this morning and that tank was 33MPG which I believe is pretty good. Really close to just going and getting the code disabled.
 

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o.o cats cant be that expensive from a scrap yard... yeah used cat but would of been cheaper and easier then the time invested removing and reinstalling the o2's

and yes i have a scrap yard cat on my SAP after i melted the old one and parts of my engine running a pzev ECU on my car.. paid $40 for the scrap yard cat.
 

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Only 100k. Its hard for me to believe this is normal if the cat is the problem. I've owned two vehicles that I bought brand new and put over 200k miles on them and never had to replace an O2 sensor or cat on either of them.

107,xxx miles on my focus. It has a dual cat. Top and bottom sections. My top cat crumbled and clogged my bottom cat. Don't be surprised by a failing cat
 

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107,xxx miles on my focus. It has a dual cat. Top and bottom sections. My top cat crumbled and clogged my bottom cat. Don't be surprised by a failing cat
o.o do you still have said dual cat vehicle?? would like to see any pictures of it?
 

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Yea. It's the zx5 I have. The tube on the outside looks like a normal cat. But the inside is more like a peanut shape. Each circular part has the honeycomb catalyst with an o2 in the middle. Literally the top part crumbled and clogged the bottom.
This is the only pic I have of it. It's emptied now
https://ibb.co/nk208G
 

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Discussion Starter #31
Wow that's nuts! I would think there would be a noticeable performance difference there with the blockage. Was there?
 

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Discussion Starter #32 (Edited)
So, bringing this back. Still have my code. I finally have a new OBD scanner. I did some logging and the down stream O2 sensor voltage is stable most of the time which is good, but it periodically dips down real low which is not good. From what I read the upstream sensor goes up and down in voltage, then the downstream one should be steady, if the cat is working properly. So I don't know what to make of it the fact that the down stream one tends to be good, then dips down real low. It seems to do it more under load. Maybe I should look for scrap yard cat.
 

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Usually when a cat fails, the downstream sensor starts switching similar to the upstream. The reading from the downstream sensor should be relatively steady when all is functioning properly. Have you checked for small exhaust leaks forward of the sensor?
 

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With all the struggling and trying to trick the system you've done, why havnt you tried a new O2 yet?

Yes the upstream will jump up and down quickly in the range of 0.1-0.9V, downstream should be steady. With your issue, it's either loose wiring that's moving when it's under a load and loosing connection, or a bad O2.
 

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Discussion Starter #35
Thanks for the replies guys. I did try a new O2 sensor actually and the problem persisted. If the downstream sensor was mimicking the upstream I would say bad cat for sure. I don't know. It is nice and steady then most of the time under load it will drop down, but will not go up and down like the upstream one. Will keep poking around. I have not checked for an exhaust leak yet. That could be it too.
 

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Discussion Starter #36
I collected some more data. What is this "fail" on "$21 - Catalyst Monitor Bank 1. TID $80 - Manufacturer Defined". Is it saying the value 0.8594, but the max expected is 0.7617? Is this my problem. I also attached a pic of the freeze frame data. Nothing in there seems off to me, but I could be missing something and I also don't know what every single field is and what a good value is for it. To my understanding the freeze frame data is a snap shot basically of the conditions when the code was thrown. Let me know if anyone has any insight.
 

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I collected some more data. What is this "fail" on "$21 - Catalyst Monitor Bank 1. TID $80 - Manufacturer Defined". Is it saying the value 0.8594, but the max expected is 0.7617? Is this my problem. I also attached a pic of the freeze frame data. Nothing in there seems off to me, but I could be missing something and I also don't know what every single field is and what a good value is for it. To my understanding the freeze frame data is a snap shot basically of the conditions when the code was thrown. Let me know if anyone has any insight.
So looking at your freeze data, you have too much emmisions in your exhaust after the cat. That is your fail. Your cat is deffinately your issue. Im having the same thing on my 05 focus 2.0 right now
 

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Discussion Starter #38
I finally got the code to clear. My car has three O2 sensors which I knew. I can't remember if I shared that in here. I never knew what the 2nd sensor was for or what it did so I have only been messing with the 3rd one. Well I found out the 2nd one also reads cat efficiency. I added a non-fouler to that one too and code has been cleared now for several hundred miles. The car runs fine and gas mileage is good. I don't see a reason to replace the cat until performance starts to be affected. I just wanted to write a follow up saying that I finally got it to clear and what I did. I read a lot of threads on here where people have issues and the thread dies and you never find out what the fix was. I didn't want to be that guy. [:)]
 

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I’ve replaced a number of cats over the years. Never once saw a 420 be a sensor. The computer is already doing the wave form comparison for you and that is why it threw a 420. Otherwise it would have coded the sensor. Sorry but it’s a new cat or a cheater rear o2 stand off if you live in a state that that doesn’t produce a prison sentence.
-Robert
 
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