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Discussion Starter #1 (Edited)
So here's a quick question with a long story. I have a 2006 GS, that is probably more factory than when it came from the factory. This is my everyday driver as I needed something that could handle the 100 mile/day commute. Anyway CEL came on a couple of years ago, had the codes read and it was supposed to be an O2 sensor (don't know which one, didn't know it had more than one) Have I mentioned that I'm pretty ignorant of new engine technology? My other vehicle is a F-250 diesel so I've been out of the loop for a little while. Anyway I even mentioned this at my dealer and he told me that if I wasn't seeing a fuel milage problem that is was probably just the pre-heater in the sensor, and that was probably what was throwing the code. So like any good moron, I ignored it. So skip a couple of years and we're at the present with 125,000 miles. Took it in last week to have the belts changed and the plugs changed out, and of course to try and get the CEL fixed. When I picked it up they had read the codes and told me it was the O2 sensore, but forgot which one, told me to swing it back by when the light came back on and they would read it again. On my way home I noticed the exhaust seemed to be louder and the pedals had more vibration in them. The car also seemed to be a lot more sporty with much less backpressure noticed when I shifted gears. So my immediate thought was, bet they left something loose on the exhaust when changing everything out. Anyway the CEL came back on the next morning on my way to work, so I took it back by that night, except this time it's throwing PO421 and PO431 codes with no mention of O2 sensors. I had him listen to the motor and he couldn't hear any exhuast leaks, and then I took it to a muffler shop to check the cat(s). They said the main cat checked in speck, but they couldn't check the precats. But they told me that the were all running hot. So at this pioint I am completely lost, and looking for suggestions...any help would be greatly appreciated. And before the obvious is mentioned this is a mechanic that me and my family have used for years, who drives and works on imports and has always done a great job, so I don't think he is pulling any tricks.

Also in summary, the car has no mod's whatsoever, the plugs were replaced with NGK Iridiums and the timing belts and drive belts were all that were replaced. It doesn't run rough at idle and the increase in sound only seems to become evident at around 2000 rpm, increasing up to ~4000 RPM.

Thanks,
Josh
 

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odd that the car felt more responsive with the 3rd cat on.reason i say that is because it sounds like your precats came apart but the 3rd cat should have stopped the broken pieces from exiting the exhaust and therefore should have felt more sluggish because of the blocked exhaust.sounds like header time.
 

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Discussion Starter #4
odd that the car felt more responsive with the 3rd cat on.reason i say that is because it sounds like your precats came apart but the 3rd cat should have stopped the broken pieces from exiting the exhaust and therefore should have felt more sluggish because of the blocked exhaust.sounds like header time.
That's what they said at the muffler shop, althought they couldn't test the precats, he said that when they went they usually jammed up the 3rd cat. But according to him, there was no resistance in that cat at all (within spec at least).
 

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maybe they broke in such away that they are not totally dislodged yet.at any rate,you can bet they will be in time if you dont either gut them and try running spacers on the lower o2 sensors(until you can get it fixed),get a oem replacement,hella expensive,(maybe someone on here will let theirs go cheap),or get a rre header and find out how to keep the cel light off
 

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P0421 Warm up catalyst efficiency below threshold (cylinder 1, 4) P.13A-612
P0431 Warm up catalyst efficiency below threshold (cylinder 2, 3) P.13A-614

You have two pre-cats that are side by side and are part of the exhaust manifold, so both pre-cats are reading the same problem.

P0421/P0431 are the same basic codes except for different banks, Page 13A-612
http://tearstone.com/eclipsefsm/2006_PS24S_MMNA_SM_PDF/GR00005800C-13A.pdf

Sensor (The sensor below is determined to be normal)
•Mass airflow sensor
•Engine coolant temperature sensor
•Intake air temperature sensor
•Barometric pressure sensor
•Throttle position sensor
•Accelerator pedal position sensor

TROUBLESHOOTING HINTS (The most likely causes for this code/s to be set are)
•Cylinder 1, 4 side catalytic converter deteriorated.
•Cylinder 1, 4 heated oxygen sensor/s failed.
•Exhaust leak.
•ECM failed. <M/T>
•PCM failed. <A/T>

So if you've been driving it around for two-years with bad sensors, by now your pre-cats are more then likely bad by now. And if enough heat was created by the two pre-cats, then your 3rd cat is probably bad by now. You might have melted them through all the way if they are saying there is no resistictions. The only way to find this out is by visible inspection.

So what to do?? Sounds like you have a lot of exhaust parts to change out. IF your pre-cats have been hollowed out, you might only need to replace the O2 Sensors, but on your after cat sensors you will need to install spacers to trick the ECU into thinking the cats are working properly. I.E. there needs to be a temperature difference between the before pre-cat sensors and the after cat sensors. By pulling the the after-cat sensors out of the exhaust stream you create the required temperature difference. Or you can buy headers and do the same thing.

To give you an idea on parts, here are a few links for pricing.

Exhaust manifolds:
http://www.partswebsite.com/courtes...tid=10021&subcatid=20055&section=7&type=parts

O2 Sensors:
http://www.partswebsite.com/courtes...tid=30153&subcatid=30513&section=2&type=parts

RRE Headers, look halfway down the page for headers:
Road Race Engineering's 4G Eclipse Parts and Performance
 
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