clutterhead
Newbie
(This was originally for my 96 Saturn SC2 but it is relevant to any car with a "honeycomb" style cat)
A couple of months ago I got the dreaded p0420. I confirmed this by seeing that the rear o2 was not holding relatively steady, and inlet vs outlet temp wasn't much different. I cleared the code and was able to get the monitors to run all but the catalyst check. In my state you're allowed one monitor to be incomplete. I promptly went to the smog station...and failed for high HC. I was bummed out but not surprised.
Years ago I read up on a catalyst cleaning process that was taken from a research article. In this article, a cleaning solution and process was used to see if catalyst material could be "revived" when deemed inefficient over time. I remember finding a forum thread where a guy claimed he attempted the same process and was able to pass smog when he previously had failed. With the youtube video he posted of the ratios used, I attempted this myself.
For a quick breakdown, this process works for cats that become "poisoned". When a car burns oil for long periods of time (my SC2), ash deposits form in the honeycomb of the cat. The result of this is that the catalyst process is not able to take place because the precious metals that make this possible are now covered. The ash becomes a physical barrier between the exhaust gasses and the metals. The idea of this cleaning process is to remove the ash deposits without removing catalyst material. Most of us have heard of the claims that cats can be cleaned with lacquer thinner, soap, cataclean, etc. But we also know that it's all wishful thinking. At least I've never heard of any successful attempts.
My setup for this was as follows:
The cat on my SC2 is welded to the downpipe, so I needed a large container to ensure the cat was submerged sufficiently. I used one of those skinny rectangular blue plastic recycle trash cans I had lying around.
-roughly 10 gals of water
-1.6 lbs of citric acid powder (amazon)
-1lb of 99% oxalic acid powder (amazon) I did not use wood bleach like the youtube guy used because I was able to source oxalic acid on its own.
-Immersion pool heater (amazon). I got a cheap one. Use caution. There were reviews stating the water becomes live with house power when its on and I wouldn't doubt it. Don't touch the water or the cat with the immersion heater plugged in.
-10+ lbs of baking soda
Be mindful not to breathe this mixture in. I didn't use respiratory protection, but I was in a well ventilated area with a downdraft and was mindful of how long I was in close proximity of the mixture. It's because of the oxalic acid. It's not insanely dangerous, but it is an irritant for sure. I did use a pair of thick nitrile gloves I got at home depot though. I wasn't about to touch that stuff. Fumes come out of this mixture when heated but don't be alarmed. It's normal.
Stir the mixture well with a stick or piece of wood. Remove the rear o2 sensor and put the cat in the mixture. Set the immersion heater to 150f. I left this going for 6 hours. Every hour or so I unplugged the heater and pulled up and down on the downpipe to agitate the mixture through the honeycomb. In the research paper they used a pump to recirculate the mixture into the cat during the cleaning process. I wasn't going to go that far. If you wanted to, a cheap aquarium pump should work fine.
After 6 hours I unplugged the heater for the final time, pulled the cat out with the gloves on, and gave it a thorough wash with a garden hose from both sides. I left the cat to dry overnight.
To dispose of the mixture, you need to first neutralize the acids before emptying the container. It took me a little over 10 lbs of baking soda to do this. Basically, pour the baking soda in using small amounts at a time, and wait for the acid to stop reacting. It will aggressively bubble initially. Don't be alarmed, just pour in a little baking soda at a time. It will also gas off a little more at this point. Just make sure you have good ventilation and/or use a respirator if you want to.
The next day I bolted the cat up and went for a drive for about 10 minutes. Pulled over to take some temp readings. I was getting roughly about 100 degrees of difference at inlet vs outlet at idle. So I knew it at least did something. Now it was time to put it all to the test.
A week later I re-attempted my smog test. Here are the smog test results before and after the cleaning:
I was really impressed with the numbers. Everything improved.
I wanted to pass this on not only because it could save you some serious money, but because none of the aftermarket cats of today compare to the OEM ones. Unless your cat has internally cracked or has melted, give this a try and save your higher quality cat from the scrap bin.
Additional links:
Forum with youtube video link
Unfortunately, the research paper is not free to view. If interested, its title is "Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing"
A couple of months ago I got the dreaded p0420. I confirmed this by seeing that the rear o2 was not holding relatively steady, and inlet vs outlet temp wasn't much different. I cleared the code and was able to get the monitors to run all but the catalyst check. In my state you're allowed one monitor to be incomplete. I promptly went to the smog station...and failed for high HC. I was bummed out but not surprised.
Years ago I read up on a catalyst cleaning process that was taken from a research article. In this article, a cleaning solution and process was used to see if catalyst material could be "revived" when deemed inefficient over time. I remember finding a forum thread where a guy claimed he attempted the same process and was able to pass smog when he previously had failed. With the youtube video he posted of the ratios used, I attempted this myself.
For a quick breakdown, this process works for cats that become "poisoned". When a car burns oil for long periods of time (my SC2), ash deposits form in the honeycomb of the cat. The result of this is that the catalyst process is not able to take place because the precious metals that make this possible are now covered. The ash becomes a physical barrier between the exhaust gasses and the metals. The idea of this cleaning process is to remove the ash deposits without removing catalyst material. Most of us have heard of the claims that cats can be cleaned with lacquer thinner, soap, cataclean, etc. But we also know that it's all wishful thinking. At least I've never heard of any successful attempts.
My setup for this was as follows:
The cat on my SC2 is welded to the downpipe, so I needed a large container to ensure the cat was submerged sufficiently. I used one of those skinny rectangular blue plastic recycle trash cans I had lying around.
-roughly 10 gals of water
-1.6 lbs of citric acid powder (amazon)
-1lb of 99% oxalic acid powder (amazon) I did not use wood bleach like the youtube guy used because I was able to source oxalic acid on its own.
-Immersion pool heater (amazon). I got a cheap one. Use caution. There were reviews stating the water becomes live with house power when its on and I wouldn't doubt it. Don't touch the water or the cat with the immersion heater plugged in.
-10+ lbs of baking soda
Be mindful not to breathe this mixture in. I didn't use respiratory protection, but I was in a well ventilated area with a downdraft and was mindful of how long I was in close proximity of the mixture. It's because of the oxalic acid. It's not insanely dangerous, but it is an irritant for sure. I did use a pair of thick nitrile gloves I got at home depot though. I wasn't about to touch that stuff. Fumes come out of this mixture when heated but don't be alarmed. It's normal.
Stir the mixture well with a stick or piece of wood. Remove the rear o2 sensor and put the cat in the mixture. Set the immersion heater to 150f. I left this going for 6 hours. Every hour or so I unplugged the heater and pulled up and down on the downpipe to agitate the mixture through the honeycomb. In the research paper they used a pump to recirculate the mixture into the cat during the cleaning process. I wasn't going to go that far. If you wanted to, a cheap aquarium pump should work fine.
After 6 hours I unplugged the heater for the final time, pulled the cat out with the gloves on, and gave it a thorough wash with a garden hose from both sides. I left the cat to dry overnight.
To dispose of the mixture, you need to first neutralize the acids before emptying the container. It took me a little over 10 lbs of baking soda to do this. Basically, pour the baking soda in using small amounts at a time, and wait for the acid to stop reacting. It will aggressively bubble initially. Don't be alarmed, just pour in a little baking soda at a time. It will also gas off a little more at this point. Just make sure you have good ventilation and/or use a respirator if you want to.
The next day I bolted the cat up and went for a drive for about 10 minutes. Pulled over to take some temp readings. I was getting roughly about 100 degrees of difference at inlet vs outlet at idle. So I knew it at least did something. Now it was time to put it all to the test.
A week later I re-attempted my smog test. Here are the smog test results before and after the cleaning:
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I was really impressed with the numbers. Everything improved.
I wanted to pass this on not only because it could save you some serious money, but because none of the aftermarket cats of today compare to the OEM ones. Unless your cat has internally cracked or has melted, give this a try and save your higher quality cat from the scrap bin.
Additional links:
Forum with youtube video link
Unfortunately, the research paper is not free to view. If interested, its title is "Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing"
