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

I recently installed headers and deleted the cats. As expected, I am getting P0421/P0431 trouble codes.

These codes have frequently been reported when changing out the headers / cats. The stock headers have pre-cats in them and when installing headers without these pre-cats one may get a trouble code (check engine light).

Deleting the cats is an obvious mod that may result in these trouble codes. I have attempted to ameliorate this symptom by installed Fabspeed's O2 extender that includes a mini-cat ... but this has not worked in my case. Even if one were to change the stock cats out for aftermarket high flow cats, you may even generate these codes.

Here is what I have found about these codes ... The rear O2 sensors do not generate any signal until they reach a temperature of around 350 deg F or so. Once they reach that temperature, they will generate a signal and the ECU is looking to determine there is a difference in the voltage between the front and rear O2 sensor. I probably have over simplified the technology, but that not withstanding, the ECU is looking for patterns and differences to determine if the cats are up to temperature within time constraints and that the cats are operating correctly. The P0421/P0431 codes specifically state that the "Warm Up Catalyst Efficiency is below threshold". I interpret this as the ECU has detected that the cats are not hot enough withing the time period it was expecting.

I have seen several people suggesting an ECU tune to have the ECU ignore those codes, but before I go that route, I would like to hear if others have tried the method of installing O2 extenders on the rear O2 sensor. What results were you able to achieve? What is the configuration of the extender ... e.g., 90 deg bend, 45 deg bend, how far extended. Also, did you do this with after market cats or with no cats at all.

Thanks for any feedback ...

Steve

 

I have the Fabspeed mini-cats with 90 degree angle connector, but am getting the codes. How did you orient the mini-cats? That is, in respect to the front car is 0 degrees and the rear of the car is 180 degrees, what angle are your mini-cats pointing toward.

Steve

 

Thanks. Mine are pointing that way too. I am guessing it may be down to the calibration of the O2 sensors with the ECU. If it continues to throw the codes, I was going to try different spacers on the O2 sensors. There is also another mini-cat vendor out there as well that Vivid Racing posted a couple of posts back. Might give them a try as their construction is a bit different than Fabspeed's.

Steve

 

When I got my racing exhaust, it came with two ECUs, but they were for the Euro Challenge cars. Incorrect part ... was not even for the US spec Challenge Stradale. I found this out after installing them and getting several trouble codes. As I recall things like fuel trims and what not. The kit did not include any O2 sensors. I complained to Ferrari about the ECUs and they acknowledged the error and they re-flashed them for me.

Steve

 

In the time since I lasted posted in this thread, I re-installed the cats. I found the cat-delete pipes were just too loud for me. So, my configuration is Fabspeed headers to the stock cats. But I am still getting random P0421 / P0431 codes indicating Warm Up Catalyst Efficiency Below Threshold. The only thing I can think of is that the Fabspeed headers do not have pre-cats as do the stock headers.

I am at the point of thinking one of these three conditions ...

1. I might have O2 sensors that are marginal.
   
2. The catalytic converter(s) could be marginal ... but the codes P0421 / P0431 are random (one of left bank and one for right) ... seems unlikely both cats could be marginal ... but I have seen stranger things.
3. The elimination of the pre-cats in the stock header is throwing off the two inline O2 sensors in each exhaust side.

I am ordering a pair of Big Daddies Mini cats and hoping that fixes the problem.
http://www.bigdaddiesgarage.com/mini-cat-cel-fix.html

Wondering if anyone else experienced this.

Steve

 

Hi Dan,

Your experience reinforces my belief that merely eliminating the pre-cats is not the problem. If the mini cats do not resolve the issue, I will probably replace the O2 sensors. Keeping my fingers crossed that the cats themselves are not going south.

Steve

 

My headers are wrapped as well. On a 360.

I am going to go the mini cat route and killing the battery power overnight is easy enough to do. No harm in that. If I continue getting those codes I will get new O2 sensors.

Steve

 

I got a couple of mini cats heading my way to install. I’ll be trying those first. I surely hope it is not the cats. Those bad boys are costly.

Steve

 

That is quite the story. I feel badly that had to go though all that.

In my case, I started by replacing the headers and added cat delete pipes. I also installed the Fabspeed mini cats. But I started getting CELs and I didn’t like the excess sound level without the cats. So I put the stock cats back on without the mini cats. Car was running fine for a bit with no CEL so sold the Fabspeed mini cats. Now the CEL is coming back. Right now the only configuration difference from stock is the Fabspeed headers that do not have pre-cats.

I ordered some mini cats from Big Daddies Garage and hope the takes care of the CEL. I do not want to go the route of reflashing the ECUs for reasons you noted. If the mini cats don’t resolve the problem, likely put new O2 sensors on.

Steve

 

My configuration is Fabspeed headers, stock cats, CS exhaust. Of course you know I am getting CEL but I will keep you advised on progress.

Steve