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Old 03-20-2015, 02:22 PM
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Catalytic Confusion

Hi! I have an 04 limited with the 4.7l. I have been getting the p0420 code so I did a treatment with the Mr Gasket engine and exhaust cleaner, Ran a full tank of gas after that and the code came back. I think I want to try changing my oxygen sensors, but I'm not sure how many I have. I saw another post somewhere that there are two, one before the cat, and one after the cat I have the Y pipe with the twin cats and they seem to each have a oxygen sensor in front and in back I don't have the rear cat, just the Y pipe. I was thinking about just changing the Y pipe. I saw a magnaflow pipe and I plan on eventually changing the exhaust to a magnaflow exhaust so that is another option. any suggestions?


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Old 03-20-2015, 04:28 PM
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Re: Catalytic Confusion

First check for any leaks at the exhaust manifolds and pipes, because this can influence the O2 sensor readings. Secondly i would put a scanner which shows live data on the jeep, to see how the O2 sensors are behaving. The two before cat sensors (bank 1 and bank 2 upstream sensors 1-1 and 2-1) should fluctuate between 0.2 and 0.8V. The more frequent they change, the better the O2 sensor is. The code you have is for bank one, so you should look at the 1-1 sensor (but can use the 2-1 as a comparison)
If this looks ok, then look to the downstream sensors (the 1-2 and 2-2 sensors). These sensors should give an almost steady output voltage. When the catalitic converter doesnt work well, then the O2 output will start fluctuating like the front sensor.
To look at the O2 sensors voltages, the engine should be warm (closed loop mode), otherwise the PCM (powertrain control module) will not use the O2 sensor readings (open loop mode) and the 1-1 and 2-1 sensors will not fluctuate. Also if you dont have a scanner with live data but you do have an android phone, then you could buy a cheap ELM 327 bluetooth dongle (+- USD 15 from e-bay or Amazon) and download the free app "Torque". This app also shows you PCM fault codes and can errase them.
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Old 03-23-2015, 11:00 AM
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Re: Catalytic Confusion

I checked the voltages and all 4 O2 sensors are bouncing around like a superball on crack!! I ordered a Magnaflow Y pipe assembly and I'm going to get 4 new sensors... That otta do it! I intend on adding on the rest of the magnaflow exhaust when I gather more spare change. The bolts going to the manifold don't actually look too bad, but the connection to the rest of the exhaust is pretty crusty. Should've an interesting driveway job LOL. Anything else worth checking out while the Y pipe is off that otherwise would be hard to look at?


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Old 03-23-2015, 02:23 PM
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Re: Catalytic Confusion

Since the O2 sensor voltages are bouncing around, they are doing their job well, so you could save yourself some money now and re-use them. If you would go for new, then only OEM (which is Denso). Ive got mine online for around USD 30 each.
I removed the Y-pipe once to be able to remove the oil pan. I wanted to do that, just to check the pump inlet screen for foreign material. I did find a piece of aluminum on the screen, most probably coming from an oil can seal. Quite a hell of a job to get the pan of without destroying it and you will need a new oil tray (with embedded seal).
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