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  #11  
Old 07-11-2020, 03:28 PM
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Quote:
Originally Posted by Big "J" View Post
Might be in left field but, what about the gas?

My 4.8 had the P0420 (Post CAT bank 1) SES recently and had to clear it a few times with my scanner. Thought my O2 sensor was going bad as well but, wasn't sure what changed all of the sudden.
Like you, it was running good and no similar issues. The only thing that was a common factor and kinda made sense, was the gas.
Oil companies went from summer blend to winter blend which, I believe contains more ethanol than the summer blend and will jack with our sensors.
So, to help narrow down possibilities I put a half bottle of seafoam in the tank and the other half used for an injector cleaning thru an intake vacuum line (brake booster hose). No more SES, better mileage and that V8 has new life at 182K.

Good Luck!
Big J, I am having the same issue with my 4.8iS 120k miles and got the P0430 twice in about 10 days. No running issues or other codes. O2's appear to be in good working condition based on analog values in INPA. I'm hoping it's a gas issue as well, as a Cat for this car is $$$$.
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  #12  
Old 07-11-2020, 07:18 PM
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Unfortunately it looks like Big "J" left us in 2017 with the sale of his 4.8, that said, I'm sure there's still enough brain-power on here to get you some good feedback.



I
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  #13  
Old 07-12-2020, 07:30 AM
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Originally Posted by Purplefade View Post
Unfortunately it looks like Big "J" left us in 2017 with the sale of his 4.8, that said, I'm sure there's still enough brain-power on here to get you some good feedback.



I
Thanks, I didn't get mine until 2017.
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  #14  
Old 07-12-2020, 10:44 AM
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Found a guy in YouTube that used spark plug non foulers to remedy a similar problem as yours, apologies, should have posted it last night when I had it, I will look for the link again this afternoon.

Basically he added a spark plug nonfouler to each O2 sensor, with a good coat of anti seize and screwed them back into the O2 bungs. His logic was that it pulled the O2s up and out of the direct exhaust path which kept them from recarboning after he cleaned them up. Cost him nearly nothing, may be worth a gamble if your issue is that bad.

Good luck and I’ll take a peek when I get a few more minutes.


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  #15  
Old 07-12-2020, 05:22 PM
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Originally Posted by Purplefade View Post
Found a guy in YouTube that used spark plug non foulers to remedy a similar problem as yours, apologies, should have posted it last night when I had it, I will look for the link again this afternoon.

Basically he added a spark plug nonfouler to each O2 sensor, with a good coat of anti seize and screwed them back into the O2 bungs. His logic was that it pulled the O2s up and out of the direct exhaust path which kept them from recarboning after he cleaned them up. Cost him nearly nothing, may be worth a gamble if your issue is that bad.

Good luck and I’ll take a peek when I get a few more minutes.


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Thanks, that'd be great. I googles and saw how it works. My question is, should I do it for all 4 or just the pre or post cat on the bank I'm having an issue with (Bank 2).
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  #16  
Old 07-12-2020, 05:36 PM
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If memory serves, he just did the post cats. Haven’t made it back to my home office yet, but I will look for that asap.


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  #17  
Old 07-13-2020, 09:41 PM
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You can get these nice spacers from FCP:


https://www.fcpeuro.com/products/uni...roducts-o2pair


I'm tempted to try them myself.


2002 X5 3.0 378,900 miles
2014 428i 68,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration
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  #18  
Old 07-13-2020, 09:47 PM
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Originally Posted by srmmmm View Post
You can get these nice spacers from FCP:


https://www.fcpeuro.com/products/uni...roducts-o2pair


I'm tempted to try them myself.


2002 X5 3.0 378,900 miles
2014 428i 68,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration
OOO thank you. So far 200 miles and no CEL. I ran a bottle of LiquiMoly engine and exhaust cleaner through, so, we'll see.
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  #19  
Old 07-13-2020, 10:23 PM
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Catalytic Conveter Diagnosis HELP!

Ahh rats - my apologies, I promised a video I have yet to dig back up. Found it this evening and it isn’t specific to your issue but it’s very similar and may have merit with helping to fix yours.

Here that is: https://youtu.be/kmOIFMqJbWc


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Good luck and keep us posted
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  #20  
Old 07-14-2020, 12:07 AM
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Quote:
Originally Posted by srmmmm View Post
You can get these nice spacers from FCP:


https://www.fcpeuro.com/products/uni...roducts-o2pair


I'm tempted to try them myself.


2002 X5 3.0 378,900 miles
2014 428i 68,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration
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Interesting looking design there. It makes a lot more sense than some of the more compact ones, although I realize in many cases stealth is a big factor and these are definitely not that.

My basic understanding of how they work, which may help answer some of the questions in this thread:

They only go on the downstream, post-cat O2 sensors.

The reason they work is that they create a mixing volume of exhaust gas that effectively averages out the exhaust gas coming through. So these ones shown here look good since they have a bigger volume (in that big fat elbow) in which the gas can accumulate and mix. They also appear to have a selection of orifices to choose from to tune how fast new gas will be cycled through there.

Basically fuel injection systems close the loop on air fuel ratio by switching back and forth between slightly too lean and slightly too rich. So the upstream O2 sensors will bang high/low at a controlled frequency, like 1 Hz or so. Then the cat converter is supposed to take those imperfect ratios and let them complete combustion within the cat, so that what comes out is a smooth signal, no longer oscillating up and down.

If a cat has truly lost its ability to catalyze those reactions, the gas coming out of the cat will be fluctuating high-low-O2 just like the upstream input. The downstream O2 sensor looks for this (an oscillation rather than the desired steady signal) and triggers the P0420 or P0430 to say the cat is not working right.

The extender things capture a little volume of gas, letting it average itself out and giving it some time to complete combustion, hopefully keeping the downstream O2 sensor readings steady.

The P0420 detection algorithm is notoriously inaccurate. You may find that installing an extender like this solves the code problems, and you still pass the sniffer test in a smog check - confirming that there was no true cat issue to begin with.
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