With a po422 code on a 2001 elantra do i replace the cat. conv. closest to the engine or the one closer to the muffler.

You may have to wipe the ecu by a pro. Or the repair wasn't done correctly either or would work

If the exhaust system was plugged the engine wont run, normally. It will start and idle until the back pressure is such that it can't take in more air/fuel mixture and then stall.

After the converter, there may be a resonator, and then the muffler. Is any exhaust flowing out of the tail pipe? You might try hooking up a scanner and see what your oxygen sensor(s) is/are doing.
Also, scan the MAF(mass air flow) sensor assembly.
Sound like the engine can't breathe, and its getting to much fuel.

Hello

If you were hot gas leaving the engine you would go through the manifold, into a small pipe, then in to the catalytic converter, down a longer pipe and finally in to a muffler. So, the Cat is closer to the engine and the muffler is closer to the bumper. You only have one muffler on that car I guess is the really simple answer.

I hope that helps you

In reading what you've already done, I would suggest a Compression Test along with a vacuum gauge hooked up to the intake manifold. It may be that you're burning oil through your exhaust system in the catalytic converter. I've seen this with leaking or inoperative turbo-chargers. Pull all of your spark plugs, marking them as to what cylinder they went in with a Sharpie and if worn, replace them. Check the distributor cap & rotor button for wear or cross-firing. A Haynes Manual for your vehicle is available through most part stores which is truly effective for your DIYer. Bad plug wires can send unburned gases down through both O2 Sensors and the Catalyst. You may also want to check the plug wires and the coil(s). A fast way of checking plug wires is to grab all of them with your hand with the vehicle running and if you get "zapped"...you need spark plug wires. Remember, the codes you pull are just a general starting point as to where to start your diagnostics, not the exact problem itself. The computer doesn't monitor the mechanical aspect of your engine nor the fuel supply. The computer will take this as a given, so don't forget that when testing that it could be a compression problem or fuel problem, but as I first said...an oil leak fouling your exhaust system such as an inoperative EGR valve or oil leak on the exhaust side of the valve train.

I hope this Helps,

"00 Buck"

either your O2 sensor is bad or possible you got a bad cat. below threshold means it detected a lower voltage than was expected.

did you disconect the battery if not disconect the battery wait 1 or 2 min and re connect the battery if all the codes come up again even the sensors you repaaced (change the computer it,s bad)

That is usually internal O2 sensor heater fault replace the sensor bank1 is the side of a V6 or V8 that has the #1 cylinder on it if ithis is a 4 cylinder that doesn't matter sensor2 means it is the second sensor in line you have 1 closest to the engine and one closer to the cat conv. if you only have 2 sensors in the system that would be the one after the cat, conv.

its the front cats that go bad on them, some were recalled check the dealer. the front cat is bolted to the exaust man.

look under truck when cool and from engine follow exhaust pipe towards back will see what looks like a small muffler [ usually about 2 to 3 feet away from engine and before the muffler] thats ur cat conv if ur doing it yourself make sure before going near cat that truck hasnt been running and is cool cat can cause extreme burns up to 1/2 hour after truck has been turned off-also some are bolted in others are welded if welded in measure before cutting old out sometimes may have get an adapter length and extra clamps

If the catalytic converter disintegrated before you replaced it, the muffler may have been clogged by chunks of ceramic falling from the cat and migrating back to the muffler.
Try this: drive the car warm, then stop and with a helper to gradually raise the RPMs while standing, listen at the tailpipe. If you clearly hear the individual firing of the engine then the system is probably clear. If you notice that the sound is more of a hiss, then either the muffler or (if it has one) the resonator are clogged.
On a car with a heavy-gauge stainless exhaust system, two shots from a .357 magnum into the tailpipe opened it up again (forever) and didn't really make much difference in the loudness of the exhaust. I wouldn't recommend doing that with most exhaust systems though.