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Hi all I’m Jeff and this is my 01 3.8 monte, bought it with 92K miles for 3.5k, was told the o2 sensor needs to be replaced and that the cat was changed before the car was purchased (p0420 codes and two others) after changing the o2 sensor at bank 1 two of the three codes cleared but the po420 code stayed, almost positive it’s the cat (trouble cranking over, TERRIBLE gas mileage, feels sluggish) but was open to hearing second opinions
I agree. If the cats plugged up, it'll definitely show with any basic IR temp gun by checking the delta from front to back.
If even the hard start is related to it, it must be absolutely toast. The engine doesn't need to flow much air just to idle, so it must be almost completely blocked for it to be causing that too. Should be very obvious on a temp check with that kind of blockage.
I would be concerned about the previous owner saying they just replaced it though - does it look new to you? If its brand new, maybe they've got some warranty paperwork on it to get you a free / cheap replacement if its a manufacturing defect? If its not a manufacturing defect and the car already cooked a cat in that short of time, that would be very concerning.
Last edited by bumpin96monte; Mar 22, 2023 at 12:10 PM.
If even the hard start is related to it, it must be absolutely toast. The engine doesn't need to flow much air just to idle, so it must be almost completely blocked for it to be causing that too. Should be very obvious on a temp check with that kind of blockage.
it only happens on really cold mornings, drove it for 2k miles now and other than the symptoms stated it runs fine, it does start to much some noise after driving it for a bit.
I would be concerned about the previous owner saying they just replaced it though - does it look new to you? If its brand new, maybe they've got some warranty paperwork on it to get you a free / cheap replacement if its a manufacturing defect? If its not a manufacturing defect and the car already cooked a cat in that short of time, that would be very concerning.
The owner told me that the previous owner had changed it, there’s a couple receipts in the car but I haven’t seen any for a cat, the EGR valve was replaced and he kept the old part in the trunk.
when I had a friend of mine check it out he said that the cat looked brand new so we went ahead and changed the o2 sensor but the po420 code stayed.
Sounds like its time to break out the IR temp gun and check inlet vs outlet temps on the cat body.
If theres something wrong with the engine that causedthe original cat to fail but the engine issue wasn't fixed, its entirely possible it burned up the new cat too.
Newbie here
