I need advice from someone who has gutted their catalitic converter or installed a header without a cat.

How are the o2 sensors going to work without the restrictive material?
I think mine might be going bad.

I have a frequent P0303 CEL code. I already tried:

swapping: coils, plugs wires and injectors

new: plugs, upper intake, egr valve, fuel filter and regulator.

cleaned: IAC valve, MAF inlet

Spark plugs all looked the same so I doubt it is a physical #3 cylinder problem. I know T/S calls for compression / leak down checks and they are next.

 

If you go with a gutted cat, or high flow cat you will throw a p0420 code, meaning the 02 sensor is detecting a problem with the flow after the cat. You have a couple of options on this, you can get someone to tune the code out of your pcm, there are a few members on the forum that offer this, look in the classifieds section, or you can get a full tune from some of the vendors that offer this and your car will run better as well, :: Overkill Motorsports :: is one that I used and am very happy with but there are others.

Second option is to get an 02 emulator from ZZPerformance | 3800 Performance Parts | Largest Aftermarket Supplier! and install it where the 02 sensor is and it basically tricks the pcm into thinking the 02 sensor is active and running well

 

Thanks Ohara

 

There's only 1 oxygen sensor after the cat, and it's only there to monitor the cat. P0420 gets thrown if you have no cat, I tuned that code out of my computer when I gutted mine.

Nice to see you hit all of the usual culprits. Check the wiring to the injector too. Rodents like to eat them.

 

Chibi you are right on about the rodents. they liked my insulation on the underside of the engine cover. Luckily they didn't go for the wires.

 

Chibi, is right. The P0420 code is for the After Cat O2 sensor. If you eliminate, Gut, Remove the cat, or get an Aftermarket Free Flow Cat, the after Cat 02 will thro that code. I have a Magnaflo cat on My Minion. It worked fine for about a month then started throwing the P0420 code. So i got the O2 Eliminator. It plugs right into the plug for the After Cat O2. I've had it for 8 months now and haven't gotten that P0420 Code. The Eliminator only costed me about $65 From ZZP.
You could also do the code delete, from one of our members or get a Tuned PCM. I didn't go that route because my inspection was Overdue and I need the car without the down time of sending the PCM out. But any of these methods will take care of it for you!