I recently replaced the coil pack and before I could manage to do that, I drove it on misfires (one cylinder maybe) for several weeks. I know, I know... but I didn't have a choice. It was either go to work or don't. I'm sure you know what I mean.
So now that I've replaced that coil pack and I have all my cylinders back, I get a sketchy P0420 code. Sometimes it is active sometimes it isn't.
So I got obdwiz and the scanner and ran a diagnostic today.
The upstream o2 sensor looks great... it's a pretty solid waveform from .1 to .9 v. Seriously looks pretty much like this:
^ ^ ^ ^ ^
The downstream o2 sensor looks roughly the same. More like ^-^_^-^^-... something to that effect.
Essentially, they kind of mirror each other. BUT my P0420 code has disappeared this morning. I'm sure it will be back though. It has done this before.
The temp on the cat is between 1200 and 1400 degrees while scanning. The mean voltage on both my o2 sensors is at .05 volts.
Everything I'm reading in this data tells me I burnt my cat out while I was running on misfires. I've read several places that that excess unburnt fuel will kill a cat, especially in these models... something to do with terrible substances in the cat, whatever.
Do you guys concur or should I look at something else first? Bad cat, right?
Also, if you guys do think it's a bad cat, what's the cheapest new cat you'd trust here:
Those cat temps wouldn't indicate a problem. Have you tried smacking the cat with you fist when it's cold to see if there is any rattling inside? If there's no sound, and it's running fine when fully warmed up (i.e. 1/2 hour or so), then I would try an upstream sensor before investing in a new cat. Or you might be able to get both O2 sensors from a lower mileage U-pull for not big $$. If you decide to go that route, I think '04-'08 sensors would work, but cross check the part numbers first to make certain of which years use the same parts.
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