I should also note that it's a magnaflow hi flow replacement......... That's what the exhaust shop put in. Another thing you guys should know is the original factory cat was replaced because it set the p0420 last winter. Upon further inspection the cat was broken up inside. (12 years old). I had them replace the cat and have been driving it fine for a few months with no issues. The distributor cap took a **** on me a few weeks ago while out of town and the truck was misfiring severely. Once home I replaced the cap and rotor and all is well now. I wouldn't think 120 miles would be enough to toast the converter. The interesting thing is although the truck was misfiring, it never set a multiple cylinder misfire code, just the p0420 (which I figure was due to the fact that there wasn't good combustion). Truck runs like a champ now I'm just fighting the p0420. I'm thinking tonight I'm going to remove the 02 (wish me luck as it looks like it's rusted into the pipe). Clean it off and add some spark plug non-foulers. I just want the light off as I know the truck is running fine. I'd drive with the light on BUT I don't want to not be notified of other potential problems so the light has to be fooled into going out.

 

I just got back from a 30 minute flogging session with the truck and the light appears to have gone out. I read on another forum that the converter may become lodged with carbon deposits and moisture from never being driven hard. Ths p0420 can be set especially with an aftermarket converter. I never went under 3K RPM's and made lots of hard pulls up hills with the ac on along with the headlights and radio. The point is to put the maximum load possible on the engine to get the converter smokin' hot. We'll see if the light sets itself again after that.

 

It's the high flow cat causing the code. The cats on my Dynatech's set off the PO420/430 code. That's really odd that you can't tune them out. I thought all GM vehicles had the on board computer by 1996?

 

This is OBD II, but no one offers a tuning solution for the 97 4.3L PCM......... Like I said, this would be done already otherwise.

 

Hirdle,

Your front O2 sensors go up and down at random times, depending on load. Hence they control fueling.... rear O2s are just for monitoring the cat. They should be more of a square wave pattern to them... not sure how to explain it, but your cat is your problem not your sensor...

 

Drove for 40 miles tonight on the interstate......... No light so far..... Hmmmm