Then it mostly is just because it's not the same OEM efficiency and just throwing the code.

 

Or it was borderline with summer fuel and now the oxygenated winter fuel has it just below the line! I know where my bet is.

 

OK so if its not actually bad (which I'm doubting) my choices are:

1) Have the PCM tuned to remove the code.

2) Put in a spark plug defouler.

3) Install an O2 emulator.

For emulators would this one work? Rear O2 Emulator: 3800 Performance This link was provided by another user early on in this thread.

If I went with this emulator do I buy anything else? Or do I just remove the rear O2 sensor and install this one in place of it?

 

This is just my opinion, but you are concerned about deleting the code from the PCM, but willing to do the Anti-Fouler trick. Essentially, you are putting yourself in the same position. You are removing the O2 from the main exhaust stream trying to fool it into not throwing the P0420 code.

If you are concerned about seeing the code when it should pop, then I'd recommend an OEM replacement cat. That way the cat meets all emission requirements that the PCM is checking for.

I've known a couple of people with brand new cats that popped the P0420 and yet nothing was wrong with the cat other then it was not OEM (they did not have fun addressing this with the shop that swapped the cat).

When a cat fails, 90% or more of the time, the car drivability/performance issue.

Ultimately, you need to be comfortable with the solution. Don't let any of us push you into something you are not comfortable with. We're all giving you a slice of our knowledge and many of us are not professional mechanics (just guys that have worked on cars a lot).

But, if it were my car, I'd fine out how to test the actual cat. If the test is good, then I would have the code deleted from the PCM or the anti-fouler trick. The reason I say that, if the test is good and you get the code, then it's just what everyone said, the cat does not meet the tight specs for the PCM, nothing further.

 

Yeah I understand I'm not being swayed one way or another just trying to take all this in and weigh my options.

I called around to a couple places a dealer included and they said the only true way to tell if the cat is bad is to cut it open and look. That's not really an option I'm willing to take.

So I believe I will have it swapped out under warranty and if it actually comes back as being "good" I'll let the garage where my nephew works at explain it to the company. As its out of my hands at that point and I can only go on what they tell me as I'm no mechanic either.

Then once the new one is in place I will probably consider putting in an O2 simulator in the rear position.

 

Total and complete BS. They can measure the exhaust pressure before and after the cat and determine if the cat is restricted.

Has the wiring for the O2 sensors been checked for opens, fraying, bad connectors, etc? All the focus has been on the cat itself...maybe it's a problem in the O2 sensor circuits...

 

That's what I was thinking I could do if I could get my hands on an exhaust back pressure tester. I called all the big auto parts stores here and nobody rents it. They're happy to sell me one but I'm not gonna buy something that I will probably use one time. I called a muffler shop and dude told me they'd have to cut it open, I called a large Chevy dealer and of course he told me the same thing.

I checked the plug wire up front and that is definitely in good shape. In fact there is a heavy rubber cover over the wiring and that is all intact. The rear O2 wiring I have not checked but I'm assuming my nephew did when he had it up on the rack.

This whole situation is why I prefer to do my own repairs. You get jacked around no matter where you go for help. My nephew I know is knowledgeable and the garage he works for is legit but I'm hoping he's not mistaken in that this cat is actually good. Mistakes do happen.

So I'm gonna let them proceed with swapping it out under warranty and THEN when I know I have a good cat to start with I'm gonna get rid of that code so it can't show up again.

 

The pressure tester is a simple handheld vac/pressure gauge. You would poke/drill a 1/4" hole prior to the cat with engine running @ 2500 rpm your specific car should show 3-5psi of backpressure, 3 being ideal less restriction. If the pressure is higher then you must drill a hole post cat and measure there it should be the same, if it is less the cat is restricted. If the pressure for both is higher than 5 psi you must remove the exhaust aft of the cat eliminating the possibility of it being the restriction, then re-testing the pre cat backpressure. When complete simply seal the holes drilled with self tapping screws.
Before you go thru all this a simple live data tester verification of the actual O2 sensors as I posted earlier in this post.
Just a question , what color is the inside of your tailpipe?
Hint this simple vac/pres tester will help you diag from front to back sort of say, a valuable tool to every tool box.

 

Actually you don't even have to drill they make one that screws into the front O2 sensor hole and you can check it right there--no drilling needed. But the damn thing costs like a minimum of $40 and like I said to use it one time and then have it sit on the shelf is not feasible.

Well my nephew did a "scan" of the O2 sensors and even offered to show me the scanner but I declined since I trust his judgment. I just hope he's not mistaken on this. He has never steered me wrong in the past. He told me specifically the front O2 was working within spec but the rear was "mimicking" the front O2 which lead him to his diagnosis of the cat being bad.

Worst case scenario the cat is good and the company b*tches about replacing a good cat under warranty. In which case I direct them back to the garage where my nephew works and let them deal with it. Since I'm no mechanic and I lack the diagnostic tools to check this correctly I can only go on what they (the garage) tell me.

 

Same thing for this fouler thing and /or the emulator they are used for when the cat is flowing to fast and the O2 sensor cannot sample the exhaust path as it is to fast. Then the O2 sensor is moved to get out of the fast track and given the chance to sample more correctly. This is why some factory installs have bends associated with one of the O2 sensors. Then customers/owners do mods to remove the restrictions and end up doing more mods to fool/ trick the system another way. The emulator is usually used for the same reasons just a different way of doing it.


It is not the front O2 sensor that calls for the code it is the rear that says wait a minute there is little or no change from front to rear and then tells the comp to add/subtract fuel. The front simply tries to keep you at an AFR 14.7-1. There is actually more to it but this is a basic As I explained earlier the comp can only do so much then a lean/ rich condition occurs. In your case I believe it to be bordering on lean. But the simple testing will tell if done correctly.