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Discussion Starter · #1 ·
After getting a U-Bend/Resonator Delete and replacing my front bank O2 sensor, I drove out to CA from CO and when I was a few miles from my destination I punched it a few times to enjoy the lower altitude and cool temperatures. Well, I received an SES and once it was scanned it showed a P0430 for catalyst system inefficiency below threshold.

This apparently can be caused by:
- Exhaust leaks
- Bad O2 sensor
- Bad cat (Bad, BAD cat!)

Anything else? I haven't checked my exhaust for leaks around the new UB/Res delete or tapping the Cat. If the cat seems fine (doesn't smell like rotten eggs) and I can't detect any leaks, I guess I'm going to jump the O2 sensor with a 100K ohm resistor to spoof the PCM. Could this be potentially bad for my vehicle's PCM? Anything else I can try without replacing my O2 sensor (or putting in a spoof, as the SMOG Nazi's wouldn't like seeing a disconnected O2, even behind the CAT.) I tried resetting the PCM and deleting the code from memory, but it came back. I don't really want to spend money on a part that just tells me that my cat may be bad, need that money for a CAI and a 3.4" pulley, dangit! :D

Any and all help is appreciated!
 

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Howdy,

I am assuming that you have a converter. P0430 will set
if the post cat o2 is hosed, or usually will set if the converter isn't doing it's job. The post cat. o2 monitors the effectiveness of the converter. If exhaust samples indicate a
"lazy" catalyst, the code will set,


BIG JEFF
 

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Discussion Starter · #3 ·
Which basically means I need to upgrade to an R/T 3" DP and cat... nice. There's another $330 out the window! LOL.
 

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nope, that will still set the code...that is what i have. You can buy the O2 spoof from a grand-prix parts site for less than 30 bucks. that will shut the code off :D

kent
 

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Discussion Starter · #5 ·
I wonder if the P0430 code can be deleted from the PCM via custom programming? That way I can have the R/T Pipe, and O2 sensor (working or not, just to fool smog places) without the code coming back on ever again? Anyone get this done or know if the DHP Powrtuner or other programmable PCM software is capable of doing this task?
 

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Discussion Starter · #6 ·
I'm such a moron, it's a P0420 code, but the same issue, catalyst inefficiency. I just got back from a 1500 mile trip out to and back from Las Vegas for a TDY to learn a new skill for my job in the AF, and got on average around 24-26mpg the whole trip, with it set to 75mph on the cruise control. I'm thinking clogged cat. I've done all the maintenance on this thing up to now (since I bought it, only thing left is transmission fluid and filter change, but that'll have to wait) so I'm pretty sure it may either be:
1. Leak
2. Clogged Cat
3. Bad Sensor

Let's be frank, I highly doubt a bad sensor or a leak would cause the poor MPG, and the car should feel a bit "peppier" than it currently does. I'm planning on taking the poor heap out to get diagnosed at a few exhaust shops to see if they agree that it's the cat. I'm planning on getting the R/T 3" DP and Hi-Flow cat, and getting that installed. I know it'll probably throw the same code, it's just the gas mileage that's killing me right now. I may get an O2 sensor sim to get rid of that problem. Ideas?
 

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Ok the code p0420 catalyst inefficiency means that the cat is not doing its job(cleaning up the gases), rarely is it a sensor problem, the post cat sensor is for monitering the cat only, it does nothing else......the front sensor reads the gases before the cat, it fluctuates up and down on the Mv scales, always moving up and down on the scale, now the gases go through the cat and get cleaned up, so the post cat sensor just kinda hangs in one spot so to speak(not fluctuating).....now if the cat isen't cleaning the gases up enough that post cat sensor starts flucuating like the front one, so it sets a code.
 

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Discussion Starter · #8 ·
So the bottom line is I need to replace my cat? I don't mind doing it, and I'll just upgrade to the R/T DP with the cat to accomidate future mods. Any other worthwhile alternatives to the R/T DP?
 

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yeah a straight through D/P, hehe....J/K, the D/P cat is great, the one on PFYC.com with the Random Technology cat is awesome, I like my random tech cat.....just make sure you use a dummy sensor, because a high flow cat at higher rpms can't clean up the gases to well, it works ok at low rpms, but when you get on it the light will come on
 

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Discussion Starter · #10 ·
Sounds familiar. If I clear my code and drive for a while, it stays gone until I get on the car, then it comes back like a bad meal... is this a pretty good sign that the stocker's toast, and will it explain the loss of MPG as well?
 

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yeah the stock cat is losing it.....the rear sensor only monitors the cat, it has no other function, your lose of MPG is from some thing else
 

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Discussion Starter · #12 ·
I understand the rear O2 sensor only monitors the CAT, and the front O2 sensor controls fueling. Even if the CAT is going, is there any chance the CAT is slightly plugged with toasted internals causing the loss of MPG? I do NOT want to chuck $500 at this car and not get my MPG where it should be. I don't flog this thing and drive it very conservatively for the majority of the time I drive. What else could it be? Torque Converter issue or something in the transmission?
 

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1 1/2 lb of back pressure from a plugging cat would cause a low power concern, the car wouldn't get out of its own way, and it dosen't take much of a plugging to cause that to happen...if your trans has a slippage or TCC problem it knows, it would set a code..... also miss fire and other sensor will set codes...... now I have seem O2 sensors alittle off and not set a code, but yet cause a rich condition, a scanner helps there, or when in doubt replace the front sensor....... NOTE: a rich condition can be hard on the cat convertor
 

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Discussion Starter · #14 ·
Agreed, I need to purchase a scanner to get the LTFT's and such to help with diagnosing the real problem. The front bank O2 sensor was replaced with an AC Delco sensor about 5K miles ago, so I doubt that the sensor is the cause. Anyone got $190 to "lend" a struggling L67 buddy? :D Seriously though, if anyone in the Denver area has a scanner, any way you can hook a brother up? :D
 
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