Okay guys, I've searched the forum for a couple of hours now and even though I found some similar threads, I can't seem to find an actual solution to my problem. Here goes:

For the last couple of weeks, my catalytic converter has been rattling. It started out only doing it a low RPM but it eventually got increasingly worse and started doing it all the time. Last Thursday, the SES light came on when I was on my way to work.When I was on the way home I lost a significant amount of power and it started to spark-knock really badly under a heavy load. I had the codes read in it was the PO420, catalytic converter deficient or something to that effect. Well, I let the truck sit on Friday, bought a Magnaflow cat (here's a link to the Summit P/N: http://www.summitracing.com/parts/MPE-53006/) and Thrush Welded muffler and had them installed this morning. The guy was nice enough to clear the code for me and I decided to take a drive to enjoy the new system. As I was driving the SES light came back on. When I got home I cleared the code and drove the truck to my parent's house this afternoon (about a 60 mile trip). The light was off the whole trip until I got off my parent's exit and got stuck at a red light. As I was waiting, the light came back on. The truck runs great but I can't stand that light being on. What exactly is my problem? Is the post-cat O2 sensor reading different flow rates and causing the code? Should I get a simulator or have the PCM re-mapped to erase that sensor's coding? Or am I jumping to too many conclusions and there's an easier fix? Sorry for the long post but I despise trying to decode information from people so I like to give a good explanation of everything I've observed. Any help is greatly appreciated. And on a lighter note, I highly recommend the Thrush muffler. Sounds great and was cheap to boot, lol. Sorry guys, I forgot to add this last night when I posted. I just recently did a major tune up (plugs, wires, cap, rotor, fuel filter, basically everything except the air filter because a CAI is in my near future.)

 

Have you read through P0420 Explained? When the SES illuminated the second and third times did you get the code read again or just assume it was still P0420?

 

I found that yesterday and skimmed over it but I haven't had a chance to perform all the actions it asks you to. The 2nd time the SES came on I read it myself with my father-in-law's scanner and it was the PO420. After the scan I deleted the code myself and drove to my parent's house (mostly interstate and about 60 miles) and the light didn't come on until I was about 5 miles from their house and stuck at a red light. I understand now why it didn't come on until I was stopped because the module scans at idle rather than at speed. When I deleted the code at my FIL's house I was only a few minutes from the interstate so I don't know if the truck had enough time to make it through a complete coding cycle to evaluate for problems. I haven't had the light checked again but I'll try to have the code read this evening and give you an update.

 

I would recommend going through all of them.

 

I'll take a look tomorrow and see if I can find any frayed wires or anything that looks out of place. The muffler shop that I went to did use the stock pipe from the cat to the muffler so it's possible they damaged the O2 sensor or I damaged it when I was driving home with the rattling cat. I'll do some investigating tomorrow and let y'all know what I find.

 

Since I last posted I've been over the items in the link posted above and I have a few new things to report. I looked underneath the truck the other night and everything seems to be in order. The oxygen sensor and wire don't seem to be damaged. Sunday night I decided to do the last simple thing that I hadn't tried yet. I unhooked the negative battery cable for 10 mins or so and the light went off just like I expected. I drove the truck on the interstate, backroads, stop-and-go traffic, in the cold, in the heat, you name it and no light; until this morning. I left for work just like normal, and as I got off the interstate at my exit I had to sit in some traffic waiting on the light to go green. I wasn't stopped 10 seconds before the light came on again. I'll see tomorrow what code it was but if it's the PO420 I'm going to seriously consider getting the PCM reprogrammed now that I've got a high-flow cat and muffler and I'm getting a CAI soon.

 

hey, i got a 2002 blazer with the two cats cut out and one magnaflow high flow cat. i have the same code also, the reason your getting that code is because the magnaflow cat will not burn has efficent has a stock cat, meaning its not doing the same job has your stock one, the oxygen sensor is programmed to read what the stock one is suppose to do. so when it sees a large difference it sends a code saying that your cats are not doing its job. i have been driving my blazer for almost a year with that now and it doesnt make any difference to the truck or anything. the sensor is still perfectly fine. if the oxygen sensor was out of wack the code would say oxygen sensor circuit malfunction. so the way you get rid of the ses light is to buy a oxygen sensor delete kit or theres ways of fooling the sensor so the light would turn off and no more code.