P0420

I've had this code since I got the truck little over a month ago I believe that's why I'm only getting 15mpg anyways I've tried adding a gallon of lacquer thinner to half a tank of gas didn't work so the only other option I see if indeed the converters are dirty is taking them off and leaving them in soapy water but as I looked at the exhaust system setup it looks to me like the cats and the headers are one solid piece or is that a resonator and the latter piece is the cat as you see in the diagram below my initial thinking was that number 3 was the cat/header combination but now I believe number 6 is the actual standalone cat please correct if I'm wrong? Also if anybody know of a good aftermarket alternative to OEM cats I did want to my my truck louder for those that can shine in on the fuel economy issue here are a Few details, I changed sparkplugs about a week ago with OEM even after that I'm still getting the same 15 mpgs I have stock 16" steelies wrapped in bfg a/t 265/75 and I have a k&n shortram intake installed

One more thing is bank 1 driver side or passenger side cat?

 

Bump

 

I don't know the answers to all of your questions but here goes:

-The truck has 4 cats, the rear two are not monitored, so one of the front two cats must be bad

-If the error code relates to a cat issue, the ECM could be messing with the A/F ration and causing you to get poor mileage.

That's all from me.

 

Thank you sir

 

The cats are monitored by the two O2 sensors right behind them. Just as a note, a bad sensor could cause it to set a false code. Make sure that the O2 sensor for the failed cat is not sending erroneous data.

 

I know that also an exhaust leak could cause the code too

 

So now I also have P0430 too

 

Real mature asshole I was getting the code before that incident happened

 

I don't know why but I thought it wasn't good to run diesel in a gasoline engine...

 

I hate to say it but you're asking for advice on troubleshooting over the internet, it might be good to include all information. While the diesel incident might have happened afterwards, it could be why you're continuing to have issues. You're combating multiple issues. Also, I've read the whole bit on running laquer thinner to help clear the code but I'll be damned if I put that shit through my fuel system... Personally, I can't imagine what would possess someone to do such a thing. Running things like diesel or laquer through your fuel system might be why you're having trouble with your cats and/or O2 sensors.

Also, you don't soak the cats in soapy water, it's a mixture of chemicals, I can't remember which ones, and it's supposed to restore the cats. Soapy water won't do anything.

 

laquer thinner?? damn that cant be a good thing for fuel lines or anything else for that matter

 

Wouldn't lacquer thinner just melt the lines?

 

It's supposedly an 'old school' method for cleaning the cats and clearing the error code. That being said, there's no way in hell I'd give it a go.

The idea of soaking the cats to restore them might work. I've only seen it done online and again, not sure I'd have the balls to try it out but it makes more sense. It's just a chemical cleaning that restores the cats. At least the bath has no chance of hurting the engine's internals and fuel delivery system.

 

You added paint thinner to your fuel tank....WTF? That'll only hurt your cats more. DO NOT do that again. You can't "clean" your cats either. Soaking the cats in soapy water will just make a mess. And get even more junk into your cat. Bank one is the left side, or drivers side of the engine(check a diagram to make sure).

Hmmm...a few flaws here.. OBDII specifies that the catalyst MUST be monitored for efficiency. That's why post cat 02 sensors exist. They monitor catalyst efficiency. If both sensors (pre-cat and post-cat) read the same thing...there's a problem. 95% of the time a P0420 means your catalysts are on vacation, and won't be coming back.