arock24

iTrader: (4)

Codes just popped up over the weekend at the same time (no previous DTCs) but the car seems to run fine. I'm confused as to how these codes co-exist? How does the cat cause a "random misfire?" Wouldn't be too disappointed if I needed to replace the cats, looking to open up the exhaust from the cats to the back. Any input or previous experiences with the following codes? Everything I searched had multiple DTCs, these are the ONLY two popping up for me..

Homer's Uncle

P0420 did not cause P0300, misfires can lead to catalyst failures but in your case more than likely a coincidence that both codes came on at same time.

P0420 set because PCM determined that oxygen storage capabilities of the
converter has degraded below a calibrated threshold. Bank1 or driver's side cat is ineffecient or worn out.

P0300 random misfire even though your not noticing it, the PCM is picking it up. You could try a spray bottle and wetting down each plug wire individually to see if you detect misfire. If that works you could narrow problem down to what cylinder, but if not lot easier to diagnosis with a scan tool by looking at misfire counters.

Chris

arock24

iTrader: (4)

Appreciate the input. I have new plugs/wires already so I might as well throw those on and see where it takes me. Any other possibilities for the p0420 code or should I just expect to replace the cat?

garygnu

can you run with out CATS in your state ?if so remove them and have a tuner delete them.

arock24

iTrader: (4)

I wish, pretty strict emissions in my part of MO (hence the shorties).

HibachiZ28

iTrader: (5)

Alex, were you able to fix the problem with new cats, new o2's, etc.? I have the same codes and the misfire is BAD!

arock24

iTrader: (4)

Not sure who Alex is, but the issue was a bad cat. I went with longtubes/ORY and it solved the problem after the tuner corrected everything. If you're on a budget, have the cats gutted and have someone tune them out and you'll be good to go.