engine code po420??

[NissanGirl81]

i need help. i just bought this 02 altima and there is an engine code already.the code is scanned po420. which i am aware of the possiblities, the cat converter, vacuum leak, engine misfire, fuel system failure, oil leak into the exhaust. does anyone else have this problem and what is the most common thing it could be? when i shift the car the rpms dont drop like they should so i am leaning towards the leak but i have looked all over that car for a vacuum leak and cant find one. any suggestions???

[xorcst]

maybe a damanged exhaust manifold?

[Racingline]

You most likely have a failed pre-cat. they are quite a common issue on the 02-06 altimas.

They are very expensive ($600 range) so be ready. Depending on how bad it is I wouldn't leave it either. If they fail completely chunks of the catalyst material can break apart and get ingested back into the motor causing serious damage.

Do yourself a favor and get either a Stillen header or XS header and weld in a universal cat under the car. Will be cheaper and will yield quite a bit of extra power. In your case likely up to 20hp (based on your cars current condition since your cat is severely clogged)