I just cleaned my 15 year old factory fitted catalytic converter using the citric acid/oxalic acid heated to 150F for about 5 hours method and to my surprise, it worked!
It cleaned up the honeycomb inside the cat quite nicely. All the light grey carbon is gone leaving clean metal on the inside. I have to say I'm quite happy that this method worked so well. No more P0420 code!
Here's the story....This is the factory cat from my 1999 Dodge Grand Caravan 3.8 that had about 475,000 miles on it when the P0420 code kept coming on back in October of 2012. I took the factory cat off, put it behind the shed and replaced it with a new Magnaflow aftermarket cat from O'Reilly's.
While the Magnaflow fit very well and appeared well made, it didn't last long, only about 65K miles before it repeatedly set off the P0420 code.
This Magnaflow cat was in my opinion, inferior to the factory cat because it was shorter, made of thinner metal, the flex joint creaked over bumps and for some reason, it set up weird resonances through the van at certain rpm's.
When the factory cat and the Maganaflow were placed side by side the factory cat measured about 9.25 inches long on the catalyst section and the Maganflow measured about 6.25 inches long. The width of the factory cat was 6.25 vs about 5.75 for the Magnflow and the thickness of the factory cat was a good 3/8th's thicker as well. I felt the added length, width and thickness and what felt to me to be thicker and heavier metal made the factory cat much quieter.
I noticed the added noise when I first installed the Magnaflow but at that time, I didn't know how to revive my original cat, so I just lived with the added noise and vibration.
This spring I started getting the P0420 code on my Magnaflow so I decided to research cleaning the cat and after seeing Scotty Kilmer's video on Youtube I thought, "Hmmm, maybe it's that easy, I'll try this on my old cat to see if it works"
So I took my old cat and instead using of dish soap, I used Simple Green. I soaked it in a tall skinny wastebasket for a couple of days and in the meantime researched other methods of cleaning the cat.
I found some guys using vinegar so I tried that for a couple of days after the Simple Green soak. Thinking it would be all clean, I rinsed it and dried it and put it on the van. In just 27 miles, the check engine soon light came on. Not good.
One thing I did notice now that the old cat was back on the van was how much quieter and smoother the engine felt. This confirmed my thinking that the Magnaflow was in fact creating the weird vibrations and a slightly louder exhaust note.
Because the Simple Green and vinegar experiment didn't work and I wanted that check engine light off, I looked for my receipt for the Magnaflow and discovered that it had a 5 year warranty on it so I went to O'Reilly and they promptly replaced my 18 month old Magnaflow with a new unit.
I installed the new replacement Magnaflow and it had the same louder exhaust note and vibration that the previous Magnaflow had. I wasn't pleased about that but the good news was that the check engine light stayed off.
I now felt I needed to try something else to revive my old cat if I wanted both the smoother and quieter function of the factory cat without resorting to the spark plug de-fouler trick or living with the check engine light on.
I had read about the citric acid/oxalic acid method on the Tundra Forum (and other places) and although it seemed a bit complex I decided to track down the products needed. Turns out it was easy to find both the citric acid and the oxalic acid. The citric acid, $2.99, was purchased at Walmart (in the canning section) and the oxalic acid (it's also called Wood Bleach) was purchased at my local Ace Hardware for about $8.00. Cheap.
The formula I used was 2.5 ounces of citric acid and 24 grams of oxalic acid, both at the same time, per gallon. Always wear gloves and safety glasses when mixing or handling this stuff. Do not get any on your skin!
To use the minimum amount of this mixture, I made a 4"X4" plexiglass plate that had four holes in it to match the pattern on the cat flange and put a large o-ring between the flange and the plexi plate to seal the end of the cat and bolted it together.
Standing it on end, cat end down, I then filled it with the citric acid/oxalic acid mix until it came out the oxy sensor hole just above the cat. It took about 3/4 of a gallon to fill to the oxy hole.
The cleaning process called for the cat to be heated to about 150F and because it had about five feet of tube after the cat, I hung it from the ceiling in the garage with the cat end down by using a wire. I then placed two 500W shop lights on it, one on each side spaced about 6 inches away from the cat and they heated it up nicely to between 130 and 160. I used my infrared thermometer to check the temps.
After about five or six hours of heating it, I poured the acid solution into a bucket and it was dirty, sort of a muddy grey sludge collected at the bottom of the bucket after it settled out for a few minutes. Good so far. At least something came out.
I rinsed it with the sprayer on a garden hose and then to dry it, I blew air through it for about an hour using my shop vac. After that I peered inside with my flashlight and 300+ reading glasses and I could clearly see that the areas of the honeycomb that had previously been plugged up with the light grey carbon were now clean and silver in color. Cool. Maybe, just maybe, this will work this time.
I installed the cat leaving the oxy sensor out temporarily while I let the cat warm up and dry further by idling the engine for about 10 minutes. Once warm, I shut the engine off and reinstalled the oxy sensor and took a long drive waiting for the check engine light to come on. The check engine light normally trips at 75 miles. This time it didn't! Another couple hundred miles and no light! Nice.
It's now been about 480 miles and so far so good.
I didn't take any pictures of this process but on the Tundra Forum there are pictures of what the poster there did to his cat and what it looked like when done. Mine looked similar. Clean.
I will update this post as I get a few thousand miles on the cat but so far, this method of cleaning cats seems to work quite well. And it's very inexpensive.
I'm the original owner of this van and it now has 537,000 miles on it and it still runs great.
I've posted a bit on the BITOG By-pass oil filter forum which has a bit more info on how I got so many miles on this van.
Many thanks to all at BITOG - I've learned much about keeping a vehicle running in top form the past ten years - which is part of the reason why this van is still doing so well.
Questions about the cat cleaning? Ask away.