Beating the P0420/P0430 Catalytic Converter below efficiency

If you have trouble understanding this article, better understand the role of Upstream O2 Senors first.

Try cleaning first, but find the cause to prevent it again!

If the catalytic converter is dirty I can see how cleaning it would work. Try a gallon of lacquer thinner in a 10 to 12 gallon tank. P0420 comes with just 5% below correct efficiency threshold. If it was broken, it definitely would not work. (Melted or broken up.) Also, remember, if your catalytic converter went bad, be sure to look for any leaking fuel injectors, check timing and spark, as these problems make catalytic converters go bad. (To test fuel injectors requires some advanced equipment.)

My point about trying to clean a catalytic converter, is that it just has some carbon build up on it keeping combustion gasses from getting the catalyzing metals, then cleaning it off will work. If enough of these metals are eroded away off of the ceramic honey comb, no amount of cleaning will make it work. If the catalytic converter doesn't have to be cut out of the car, then it may be practical to unbolt it and leave it in a thick concentration of dawn detergent over night, rinse it off, reinstall it and it may work again. This is a more aggressive and more effective way, but if your car is really old, my guess is that it just needs replacing.

Back to the analysis, has it really gone bad?

On a live data scan you can see the stoichiometric up and down from lean to rich on traditional O2 sensors. Seeing that on bank 1 sensor 1 or bank 2 sensor 1 - O2 sensors that are prior to the catalytic converter you're fine. If you see that same, or nearly the same wave form on sensor 2 for bank 1 or 2, then you should have a bad catalytic converter (saying this to cover V6/V8 cars with two engine banks, just apply the information to to a 4 cylinder or inline 4, (L4) engine without the bank 2 information. The sensor 2's on bank 1 or 2 are after the catalytic converter. Bank 1 catalytic converter below efficiency is a P0420, and a P0430 is a the same problem on bank 2.

I had an exhaust leak prior to my cat (a nickname for catalytic converters). When I replaced my cat I was lucky that I did indeed need it.The new cat almost stopped the wave form on the sensors behind the cat. You see, as outside air burps into your exhaust via the venturi effect (move gases down a pipe at high speeds will pull outside air in through a hole) it'll cool the exhaust gasses, and make your catalytic converter cooler for a moment, and burn less of the unburnt combustion gasses. A human can see the difference but the car figures exhaust leaks as a bad cat.The rear O2 sensors should be pretty steady. They can stay steady rich or lean and you've beat the P0420 and/or P0430.

They can go from lean to rich at times. My car's cat lives super lean, by my O2 sensors estimation. If I'm accelerating for a while onto the freeway or the exhaust isn't warmed up yet, then that sensor will go rich. Some rear O2 sensors will see rich all of the time. That's how usual catalytic converters/rear O2 sensor relationships are.

by AutoBravado

Related content:
Catalytic Converter and Horse Power, Why More HP?

Catalytic Converter and Horse Power. Why more HP? Part 1

When I replaced my catalytic converter it had to be cut out. The new one has to be welded back in. Facing all that work, I didn't even consider cleaning it as seen on Ericthecarguy's channel in this video catalytic converter cleaning. I've seen a lot of Honda's on Ericthecarguy's show and one Honda on an AutoZone show easier to remove catalytic converters with flanges. Theoretically, You can just bolt the new one one. Catalytic converters last too long and exhaust rusts, so "easy" is not how it usually still turns out. How kind of Honda to help make this possible. (Forgive me if I forget that maybe Eric had to add the bolt in flange to make that true?)

Anyway. I bought my catalytic converter (often called a cat) from Auto Parts Warehouse. First and only product I've bought from them, being fans of AutoZone and O'Reilly. I got it for $98. The reason I bought it here was because when I talked to O'Reilly's or AutoZone they wouldn't look at their database without my car in it. So, all they would see is stock cats. Only Auto Parts Warehouse out of 5 stores would work with me to look at cats by their diameter of pipe. I bought an Eastern Cat made for GM cars, which were designed to resist coolant and oil better than other cats since these leaks burned up so many cats on GM cars. It was legal in all but CA and I think NY. Catalytic converters don't have to always be expensive. If you live in CA or NY this article really doesn't apply to you (be sure to check your local laws). Since I thought I had a 2.5" catback upgrade I went with a 2.5" catalytic converter. I wanted a little more power. I went from 59 to 90.1 wHP. Not a little more!

It turns that my catback upgrade of 2.25" exhaust measures 2.5" on the outside, whoops. So, that was also a lot of extra work, but I wouldn't have done it any other way as this reduced back pressure further. Since catalytic converters are the biggest bottleneck on the exhaust getting out of the tailpipe, I figured bigger was better. I had to use pipe conversions from the catalytic converter to the down stream pipe. Plus, the 2.5" OD catalytic converter needed a 2.5" pipe into it, before the pipe converter would work. The converter and the catalytic converter were both 2.5" OD, meaning it fit over 2.5" and was more like 2.75". ID means it'd fit in rather than over. If ID and OD aren't mentioned it SHOULD be actual 2.5", not the case for the catalytic converter.

The worst part of the conversion was going from the 2.5" OD pipe of the catalytic converter to the 1.75" stock down pipe. They don't make a conversion pipe do that all at once. Took 2 conversion pipes and hours of cold steel work with a pipe expander that broke on a 2" pipe to get big enough to fit over rather than under the 1.75" down pipe. (The pipes I bought were 1/8" thick which adds to 1/4" of size for how it fits, but the stock pipe's were much thicker, maybe .375" thick.)

Back to back pressure on part 2 of Catalytic Converters and Horse Power.

by AutoBravado