Catalytic Converter Clogged - Glazed Over

Sounds like normal carbon fouling that is caused by rich running and oil burning.

 

400,000 miles!

IMO...Normal see post 2.

 

I wouldn't scrape them.
Typically, those honeycombs are fragile.
Maybe not oranges to oranges, yet look to Ferrari model 360 ingesting honeycombs for expensive "horror" stories.
Although your decision.
Good luck.

 

It must take a hell-of-a backfire to force catalyst guts back into the engine.

 

Looking for any updates.

Was the clean up enough for the 420 code to go away?

How many miles now?

 

Burning oil is the most common cause of cats going bad on high mileage Prii. The Prius' ECU is quite good at keeping the air fuel ratio right around stoichiometric, so rich running usually isn't the problem.

If you google around, you can find methods of soaking the cat in different chemicals which can keep the cat working as expected longer. However if you're burning oil, you're not really solving the problem.

The working theory on why high mileage Prii burn oil is that the piston rings wear and also get gunked up by hydrocarbons. This allows more blow by than normal, which results in additional pressure in the crankcase, which then pushes oil vapors through the PCV to be burned by the engine. There are two things you can do to help:
1. Run a few tanks of a high quality engine/fuel injector cleaner gas additive (Techron or other with PEA). Some users report reduced oil use, some not.
2. Install an oil catch can. This won't stop oil use, but will catch a lot of it from burning in the engine, helping save the cat.

You'll want to solve the A/F ratio sensor problem. It may be it just has a layer of crud on it as well, and pulling it out and cleaning may clear the code.

 

Option 3. Is piston soak method. You just pour the cleaner into the cylinder from spark plug hole and let it seep through the piston rings into the oil pan then change the oil and get the excess cleaner out of the cylinders.

If you decide to go with catch can don’t forget to empty it! In some driving conditions you might have to do it in every couple of days (especially short trips in cold temperature). And in cold catch can can freeze.

The way Toyota installed the air-fuel ratio sensor it might be impossible to remove it without breaking it so cleaning it might not be an option.

 

Amen brother!
My 2008 burns a lot of oil and (at 175K miles) the cat clogged so badly that it failed the smog test, even after lowering into a vat of acid for 6 hours.
So I replaced it (US$ 1,800) and promised myself that I would get the engine rebuilt to avoid clogging another cat.
So, here I am, 37k miles later, and I'm starting to get catalytic errors. This is what the plugs look like after 37K miles:

This time I learned about the marvel Mystery oil soak
and the catch can!
I have the cylinders soaking now and will install a catch can in both of my Prii.
If that doesn't work, then I will really have to consider a rebuild... and a quasi legal cat replacement. (it's ... complicated in California, pm me for details)

 

What weight oil are you using?

Doesn't look like you're using NGK IFR5A11 (or Denso SK16R11) plugs, what model # NGK plugs are you using?

 

Those spark plugs are excessive worn! They should have being replaced long time ago. You can see some kind of caking on the plugs, as a result of oil burning.
Get that engine rebuilt, to stop the oil leaks, or you risks getting the catalyst destroyed again.

 

I wonder....: would Oxi-Clean solution soaks work on a Catalytic Converter? Is it all stainless steel and/or other non-corrosive metals? Oxi is a moderately strong caustic, not quite as strong as Oven Cleaner. It will react with regular steel, aluminum, you'd want to avoid this.

With the 3rd gens there's a Exhaust Gas Recirculation "cooler", basically a passage with a rectangular cross section, with a small radiator coolant labyrinth, that get's carbonned up. Mixing an Oxi-Clean solution, hot tap water and as saturated as possible, pouring it and letting it soak, it reacts with the carbon, floats it off. It takes maybe 1/2 dozen hour long soaks and rinses to get it clean, very clean.

 

Coolant leaks are also hard on catalytic converters.

 

That’s why you gen 3 guys all seem to have an extra one of those.

 

I just cleaned the original, pretty much zero $ outlay.

 

The ones in the photo are ngk bkr5eix-11
I didn't think to double check when the guy at the parts store handed them to me.
The new ones are Denso SK16R11