03 impala 3.8 cat issue

[kilroy357]

replaced the cat a little over a year ago cause it was blocked up. yesterday code kicks off for it again, sluggish goin up hills, was wondering if someone could tell me where/what i have to look at to fix this. plugs and wires have been changed after i got the cat replaced the first time. ty for any help.

[Tech II]

Were you experiencing any other codes, like a misfire code, besides the P0420?

What kind of cat did you put in? OEM or aftermarket(usually smaller in size)?

Were you experiencing any driveability problems prior to the cat failing again?

[kilroy357]

that is one thing i cant remember what one the shop put on, as for driveability problems prior it all happened that day i felt it bogging out goin up hill at low rpm and a slight chugging but other than that it seems to run fine. the gas mileage has changed a bit now that i think about it. i dont really drive all that much either, doubt i put 5k miles on it since cat was replaced, since i ride with other people.

also no other code than that.

[Tech II]

Has it been scanned for codes?

This bogging down, does it feel like a misfire?

[kilroy357]

yes was scanned no other codes than p0420 one was, the bogging down doesn't feel like a misfire. it's like not downshifting when going up a hill, only at low rpm but if i give it more gas before hand it seems to have no issue.

[j cAT]

Originally Posted by kilroy357

replaced the cat a little over a year ago cause it was blocked up. yesterday code kicks off for it again, sluggish goin up hills, was wondering if someone could tell me where/what i have to look at to fix this. plugs and wires have been changed after i got the cat replaced the first time. ty for any help.

with no codes could be the fuel system. low pressure or just bad fuel.
put some techron fuel conditioner/injector cleaner in see if it improves. have the fuel pressures measured. do not allow fuel levels to drop below 1/4 tank... this causes the pump and fuel to breakdown..
dirty injectors will damage the cats..

[Tech II]

Hard to believe a cat would only last 5K with no symptoms prior to the code.....You will have to disconnect the cat or create an exhaust leak(remove O2 sensor BEFORE the cat), and test drive the vehicle to see if it is a blockage from the cat causing the problem.......

[Crvett69]

can also have cat checked with a vacuum gauge or a infrared heat monitor to see if its working correctly

[kilroy357]

had the car scanned again, the guy said the o2 sensor after the cat was going bad. i changed that, the light is still on p0420 code, has the word "pending" after it. I tried disconnecting the battery with no luck of light going out to see if it would come back on. i will try the other stuff y'all suggested and see what happens. thanks again.

[la1]

P0420 Did you have them show you it was a new cat. I had a cat that was getting P0420 and I drilled a hole in the pipe above the cat and w/ the engine running squirted in a can of throttle body cleaner (sensor safe) the code went away for a few thousand miles, then came back. I screwed a screw into the hole I made.