P0420 Code FI w/ Catted Headers

[LunarS550]

I’m assuming this will just be something I will have to live with from now on since tuners will not mess with emissions equipment, which is completely understandable.
But I’m wondering could this code possibly be a bad 02 sensor? I ran the headers NA with no issues and no codes. Now that the car is boosted I’m getting the code, result of bigger injector and more fuel or bad 02?

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[sjmurphy34]

Could be a bad O2 but only way to tell would be to swap it out. I'm not sure what bricks are used in catted headers but I'm guessing they are less loaded than the OEM bricks. Assuming they are less loaded or have a lesser washcoat on them I'd expect that they'd be more likely to set catmn codes.

The way catmn works is it is measuring oxygen storage of the bricks to determine whether the catalyst is still healthy or if has been damaged. It does this by running a DFSO event to saturate the bricks with oxygen and then when the fuel turns back on after the DFSO event it measures how much fuel is needed to get the sensor to switch. If it take more fuel than the cats are still healthy, however if it doesn't take much fuel it determines the cats are below where they should be efficiency wise. They calibrate these by using green cats, road cats, full useful life cats, threshold cats (purposely damaged/poisoned bricks used to set the threshold) and even empty cats.

So it is possible that maybe the cats are damaged already, or a bad sensor/exh leak, or the oxygen storage capacity of the bricks are just low and near where the thresholds are. Not easy to tell though unless you were able to see what the actual catmn sums are.

 

[MKL_DS]

Was it tuned for the headers prior to installing the supercharger? If so, it’s possible that the tuner had disabled those codes at that time.
My experience has been that most aftermarket catalytic converter’s will still throw these codes. They are generally too efficient to show any change from front to rear, and if you are getting the codes with these high flow converter’s, you may as well be running off-road pipes.

 

[LunarS550]

Was it tuned for the headers prior to installing the supercharger? If so, it’s possible that the tuner had disabled those codes at that time.
My experience has been that most aftermarket catalytic converter’s will still throw these codes. They are generally too efficient to show any change from front to rear, and if you are getting the codes with these high flow converter’s, you may as well be running off-road pipes.

Yes it was tuned for the headers. I keep clearing the code and doesn’t come back for a couple days. I’ve had it come back after WOT and just cruising, no consistency.

 

[MKL_DS]

I’d guess the codes were previously disabled in the header tune. Likely need to be disabled here or just dealt with.

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