SES on again (PO420)....Need Help!!!!

[nda0602v6]

About a week ago I had Autozone scan my 2002 Firebird because the SES light came on. They said the following codes came up:
po420: (Bank 1)Catalytic effiency bellow threshold.
po300: Random Misfire

I replaced the oxygen sensor on the Drivers side, replaced all 6 plugs with AC Platinum plugs, replaced the air cleaner, replaced the fuel filter and started using premium gas *93-octane.* After I did all of this the car ran great and didn't misfire anymore; just ran nice and smooth. Then a few days ago the SES light came on again and now sometimes at idle the car runs kinda sluggesh, but only for a second or two then it runs smooth. I took it in to Autozone again tonight and the code that's showing up now is the po420 code again. The guy at A.Zone seems to think I have a bad catalytic converter (a few other parts stores have suggested the same). So at this point i'm clueless. I looked under the car real quick tonight and it looks like the cat. converter is welded on to the exhaust pipe on each end; I didn't see a clamp of any kind. So I have to replace the entire exhaust??? Any suggestions on what I can do to fix this SES light? Thanks

[98Camaro3.8]

P0420 is a very common code for cars with hi-flow catalytic converters. It says the cat is not doing a good job, so something isn't right. It has no effect on drivability. The usual cure is an oxygen sensor to trick the car into thinking the cat is good.

If your car is misfiring, get that taken care of before trying to fix the cat. All that raw fuel going into the exhaust from the misfire could be playing hell with the cat. Have you replace the plug wires lately?

[nda0602v6]

No I've never messed with the plug wires yet. I think they are original (29K on the car now). When I replaced the plugs, I looked over the wires pretty good and didn't see anything grounded out or any frayed wires. It doesn't seem to "misfire" anymore like it did before I replaced the plugs and the oxygen sensor. Like I say, for a second....or so, at idle it hesitates if you will but then its fine. It has good throttle response, no lagging of anykind. And I don't know if this matters but the car always gives off a smell of rotton eggs from the exhaust....It's done this since I've had the car (had it a year now).

[98Camaro3.8]

Sounding like the cat could be going bad. The smell is a good inidcation of that, and the SES just adds to the possibility. If the cat was clogged, it could cause misfiring.

An exhaust shop can cut off the cat and weld a new one on pretty easily. A new cat should only cost $50 or so.

[nda0602v6]

Hey thanks for all the info Matt. Should I get an aftermarket Cat or stick with a GM one? Would you recommend having a new cat be welded on or do they make one to where you could slip over the old exhuast pipes and use clamps? Thanks again man

[97slowbird]

Definately welded ... I'd probably go with an aftermaket if for nothing else, the price. You can pick one up at Summit Racing for cheap and better for reducing backpressure too.

[nda0602v6]

I took it into the dealership today and they said the cat is covered under warranty [img]graemlins/rock.gif[/img] They ordered it and will be putting it on next week sometime. They said it was a $900 part...damn, it must be the entire exhuast for that price.

[navyblue2000]

Originally posted by nda0602v6:
I took it into the dealership today and they said the cat is covered under warranty [img]graemlins/rock.gif[/img] They ordered it and will be putting it on next week sometime. They said it was a $900 part...damn, it must be the entire exhuast for that price.

heh, I had my cat replaced too with about 40k on it...warrantied to 80k is a nice thing [img]smile.gif[/img]

that 900 dollar part is actually the Y pipe, cat and the small S-bend - part of what makes it so expensive (and also why they cut up bad cats and send them back to GM), is part of the catalyst is platinum.

[2002 v6 camaro uncharged]

I have the same problem with the SES codes and everything except that I have only seen the PO420. The car does not seem sluggish on take off but when it sit at idle it seems like it has a slight miss and the SES light has only come on at idle. Also, when I am driving at a constant speed I feel something like a miss, for example, if I am going 50-55 mhp in 4th gear once in awhile I will feel a chug. I just changed all the wires except one because my headers are in the way and it is hard to get to. So I will have to change that one when I have a little more time to play with it. My spark plugs should be fine since I just changed them in december. If changing that last wire does not fix the problem I have no idea what to try next. Maybe clogged injector or bad coil?

[nda0602v6]

Originally posted by navyblue2000:
that 900 dollar part is actually the Y pipe, cat and the small S-bend - part of what makes it so expensive (and also why they cut up bad cats and send them back to GM), is part of the catalyst is platinum.

The new cat is on and now the car runs so much better. That's funny you mention them cutting up old cats because when I drove by the dealership yesturday to see if the car was done yet, I saw it sitting way up on a rack with a tech standing underneath holding a cutting torch with a huge flame. :eek: Everything looks new though, from the engine all the way back to the muffler. :cool: