SCCAGT

Good idea to check this after replacing the plug(s). However, it is very possible that the misfire set the conditions for the catalyst code. It could also be the other way around.

The GM 5.3 engines in trucks/tahoes/suburbans have an issue with converters clogging up just enough to not notice mileage/power losses, but cause misfires mainly on one side of the engine.

SCCAGT

booboo

SCCAGT

i goofed

ym42

Yes, I am open to all possibilities about the 0430 cat code. I have a very primitive tool for data logging, its an ELM reader that connects to a laptop. It does not do a good job of monitoring O2 sensors for some reason. Very slow... I do not like Platinum/Iridium plugs, and use an ordinary copper ones in my 4 banger and motorcycle... But here I do not have a choice... Just changed the differential oil and about to deal with getting a sparplug exchanged under warranty if such thing exists...

ym42

Sccagt - great post! I completely agree! Now I know that Champs don't work well... I will keep you posted... May be it's just a fluke because right from the beginning there was something wrong...