Restoring old catalytic converter's efficiency (cleaning method)

[oil pan 4]

Palladium is at like a 16 or 17 year high.
Platinum is coming off like a 5 year low of 900 an ounce. I bought a few ounces, so I'm watching the price.

[Xist]

I tried to find more information on this method.

3,000 miles before code: https://priuschat.com/threads/acid-b....166554/page-3
12,800 miles before code: https://www.tacomaworld.com/threads/...d-wash.241619/
18 months and no code: (All Years) Catalytic Converter Citric Acid Bath P0420 - Subaru Forester Owners Forum
Almost 30,000 miles without a code: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread) - Page 12 - Toyota Tundra Forums : Tundra Solutions Forum
BamZipPow ran it through the dishwasher and has not had a code for 41,000 miles: http://ecomodder.com/forum/showthrea...-do-23483.html
480 miles and disappered: https://www.bobistheoilguy.com/forum...topics/3391904
Tried a few things, without clear results: https://forum.ih8mud.com/threads/cat....833570/page-2
Attempted, but did not report back: (All Years) P0420 Catalytic Citric Acid Bath (How To) - Subaru Forester Owners Forum

Who knows how accurate any of this is, but there is indication that 50% of people who try this see clear benefits, but unfortunately, it seems like hardly anyone followed the directions perfectly.

[oil pan 4]

Try hydrochloric.

[Xist]

This seems to indicate HCL would not provide the results I desire: Using Dilute HCl/Cl to Process Catalytic Converter - Gold Refining Forum.com

[California98Civic]

Originally Posted by Xist

I tried to find more information on this method.

... 18 months and no code: (All Years) Catalytic Converter Citric Acid Bath P0420 - Subaru Forester Owners Forum...

I think that Subaru link is one of the dudes I was copying in my citric acid bath cleaning. FWIW, thirteen months later and no emissions related codes (no codes at all, acutally). But I did not have a code to begin with. I had reason to suspect my 1998 OEM catalytic converter might fail emissions and wanted to be prepared. I passed emissions, barely. Then I cleaned it.

[Xist]

California98Civic was kind enough to share his cleaning supplies with me; I bought a 16 quart stainless steel stock pot for my larger Accord cat and put it on a hot plate for 10 hours. Unfortunately, the larger pot was still not deep enough, either I needed a much larger pot, much more water, and much more powder, or a turkey fryer pot. It did something, the water turned black. The water did not cover the electrolyte honeycomb, so I flipped it over halfway through, although since the sensors is in the middle I could have ignored the back half. Curiously, it ate one of my gaskets.
I did this at 179,270 miles.
http://ecomodder.com/forum/attachmen...1&d=1506362279

[oil pan 4]

Hmmm, HCl might work a little too well.

[California98Civic]

Originally Posted by Xist

... The water did not cover the electrolyte honeycomb, so I flipped it over halfway through, although since the sensors is in the middle I could have ignored the back half. ...
[imgl]http://ecomodder.com/forum/attachment.php?attachmentid=22756&stc=1&d=15063622 79[/img]

This is great. I am glad there has been no CEL for nearly 2000 miles, too! My pot was also on the small side. But the honeycomb was completely submerged for me. And I used a ladel or something to move sort of baste the top of the honeycomb. Did you monitor solution temperature at all? It is not supposed to boil, but they recommend a pretty high temperature.

[Xist]

Unfortunately, I forgot to bring my infrared thermometer, but it was never boiling when I checked on it.

Did the acid eat the coating in your pot? Mine turned green, I cleaned it, and now it is rusted!

[California98Civic]

Decided to clean my O2 sensors with this same method, rather than using gasoline on the sensors. I figured if the light acid wash was good enough for the catalytic converter, then it should be fine for its partners in crime (the O2 sensors). I used a half gallon of tap water instead of distilled. I cooked for two hours, scrubbing occasionally with an old tooth brush. Pics:

BEFORE (upstream on left, downstream on the right):


The downstream one on the right was throwing the P0420 code.

Submerged the contact area of the sensor only:


After cooking (no boiling) outside for 2 hrs, compare the above and below photo to notice the flakes of yellow and black in middle of the pot that have gathered there due to stirring:


AFTER (upstream on left, downstream on the right):


Took it for a spin of maybe 15-20 miles. All seems good, Felt like I got into DFCO easier, sooner, but that could easily be confirmation bias. Butt dyno stuff, that.