P0421 / P0431 Trouble Codes (Catalytic Converter) ... anyone have good fix?

So lets see, you questioned my hours of research on a public forum and you cant understand why Im getting defensive?

So Im asking you to back up your statement with facts and data so that we dont confuse anyone.

Here again is what I said:
On my F430 I installed Agency Power Headers, stock cats and Kline Exhaust.
Show me one post that has the exact same configuration as I have with check engine light issues.

The point is in case others would like to avoid CEL issues then perhaps they can go the same route.

 

You are misinforming members here, you are giving them a bulletproof solution for your “hours of research”
It is pretty simple your setup might throw codes in another car, because your exhaust has NOTHING to do with them, if you remove precats by changing headers you may or may not get codes.
Someone might follow your advise and saying it is bulletproof just because you could not find a single post with an identical setup that did is irresponsable and misleading.
Me for example I DID have codes and I offered OP the solution that worked for ME, will it work for him I don’t know but at least I am not pretending I know it all.
You were lucky that your setup didn’t throw codes PERIOD.
Pick up a fight with somebody else please





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Sorry Steve for highjacking your thread.

I just want to set the record straight before I say "over and out"

I never said or offered a "bulletproof solution"

All I said was - here is my configuration and I get no check engine light.

Over and out.

 

My 2004, 360 Modena has a Tubi exhaust with Fabspeed headers. Post header installation, the P0431 code came up. First attempt to fix using O2 spacers purchased from Vivid Racing (great support from James) didn't hold as the code came back after ~200 miles. I then had Big Daddies Garage Mini Cat O2 spacers installed. Code gone; things appear to be working like a charm. Installation took place last July. A couple of weeks ago, the car passed Oregon DEQ smog inspection with flying colors. Hope it's happy sailing from here.

 

Based on the similarities on configuration and fault codes identified, what do you think is the likely root cause of the fault codes being thrown?

And by the way Steve is your car a 360 or F430?

Thanks.

Dan

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FYI - I have a Euro car and moved to Fabspeed headers and DID get the code. So I would argue that changing headers from Euro to Fabspeed can cause the code, even though neither header had a pre cat material. There's a larger tube design and different collection with the Fabspeed headers compared to stock, so I expect that may play into the outcome (or maybe something else entirely...)

 

do you need the 90 degree adapter with the Big Daddy's like how the Fabspeeds come?

 

Yes, you do.

 

you are absolutely right, the difference between both readings (front and rear) should meet certain threshold otherwise it looks like the cat is not working properly, when you remove precats (by replacing headers) you are removing HALF of the scrubbing material, 2000+ models 360s have THREE SETS of cats for a total of SIX, one set inside the headers, and another two sets in the main cats, the problem is the downstream sensor is located BEFORE the main and bigger cat material, so the computer is programmed to sense the difference only using the first two sets of cats.
I hope Fabspeed does not mind if I use a couple of pictures from its website to illustrate this,
1,2 and 3 are the location of the original cat material, and 02 are where you can install 02 sensors.
if you replace BOTH headers and catalytic converters you are removing THREE sets of catalytic converters with ONE. the advantage of this is that Fabspeed cats have 02 bungs located before the CAT (if you are not removing the headers) and after the main CAT (if you are replacing both headers and cats), honestly I do not know why you would connect the 02 sensor in the first set of bungs before the main cat, even if you have the original headers I will always put them in the bungs further away.
By locating the downstream 02 sensor AFTER the main cat is PROBABLE that you would not have codes, because that bigger cat material would scrub better than the two smaller cats in the original setup.
I have hyperflow cats along with Fabspeed headers, before installing the hyper flow cats I had codes that I resolved with the mini cats 02 extenders on my OEM cats (because the longer distance the sensor is located from the mainstream the less it can sense fooling the computer that the cats are scrubbing more), when the shop installed the hyperflow cats he told me he checked emissions and he didn't think I would get a code even without the mini cat extenders, but he installed them just to be safe.

 

well, you don't "need" the adapter for the big daddies to resolve the codes, but it is WAY easier to install because of the clearance and also it lengthens the distance between the mainstream and the 02 sensor, so I would use them for sure.

 

We installed the mini-cat without the o-degree or 90-degree extender. Sorry for the bad photos... running out the door and snapped these through the glass. I'll take a couple more later. Image Unavailable, Please Login Image Unavailable, Please Login

 

I am learning so much from this post.
I will be so much more informed by the time I decide to go with headers.

Thank you Steve and others that have contributed.

 

Those "mini cat" have any honeycomb/catalytic material in them or are they just extenders?

 

They do, at least the main extenders for sure, the angle adapter I am not sure


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they have a honeycomb material in them. I had them on a 997 turbo. They only last so long on high output engines.

 

I want to summarize the troubleshooting for these codes (421/431/422/432) after replacing headers.
1 02 extenders
1* overnight ECU reset (don’t know why but it made a difference vs r resets)
2 02 extenders with honeycomb material inside them (mini cats)
2* overnight reset
3 ECU tune to ignore these triggers (some monitors will never get completed if you live in a State where this is a requirement for passing smog then this is not an option)
I believe this is about it.




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That's a great visual, Steve!

If this truly eliminates your 421/431 codes, I'll most likely do this as well. My light only comes on once a month or so but if this gets rid of it, that'll be a good $100 spent.

 

Now I understand why you could not install the adapter, the Fabspeed doesn’t have the angle to interfere because what connects to the cat (top block part) threads directly and the 90 degree is the mini cat that is connected as a second part (I will take a picture later and repost)
Don’t forget to do the overnight reset, save your self an extra step in the troubleshooting.
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I just installed new Pilot sport 4S, I needed to break in the tires so I decided to go for a road trip too!!
There is always a good excuse to do so
Have fun Steve


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