Reviving and saving an old catalytic converter
 

1996 Saturn SC2. ~220k miles

I wanted to pass on my experience to all of you, even though this really goes for any car that has 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 promply 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, or 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 the 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 had used a pump to cycle the mixture through the catalyst material. I didn't want to rig up any of that and figured agitating it every now and then would be sufficient. If you really wanted to, I'm sure a cheap aquarium pump would work

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 also will 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 when at an 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:


https://cimg5.ibsrv.net/gimg/www.sat...bbb1409c5d.png
https://cimg7.ibsrv.net/gimg/www.sat...4e328b17f8.png

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 anymore. If interested, the title is "Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing"

Your p0420 code confirms your vehicle is OBDII.

In some cases you need to drive 25 to 50 mi for the catalyst readiness test to run after clearing the code and running through all the readiness monitoring tests again.

You never said if the check engine light went out.
You never provided oxygen sensor data post cat soak.

> >> Edit <<<

You've done nothing to the catalyst. Maybe you rejuvenated your cat con by uncovering it. Would love to have post project O2 data to cement the success claim. But we don't. And we're not gonna.

But you didn't set out to prove a hypothesis using the scientific method, so I will refrain from imposing my analytical view on what you've accomplished.

Peace

Nice find, man. Thanks for taking the time to try that and posting it. This information could save some folks a chunk of cash. Derf, you should make this a sticky!

lol ok? You’re right, I totally should have known that derf on the Saturn forum is only going to believe me if I document my entire process for him. Not like I had the thought to post what I got out of this to the forum after it actually worked out and only then it crossed my mind. Where do I get off not screenshotting all my o2 data, all my diag process, taking pics throughout a few months worth of doing all of this in between a busy life? Totally not beleivable.



The code came and went many times before I did this. Long before the initial smog. I already knew what I was up against, so I got all but the catalyst monitor to run before the initial smog. In my state you’re allowed one readiness monitor to not have ran and it’s still a pass if everything else passes.



I had a consistent upstream swinging voltage on the rear o2. You snap the throttle, it tracks with the upstream in real time. Consistently hovering around .9v at idle if it ever happened to steady itself, and never really going below .5v. Classic dead cat diag. No difference between inlet and outlet temp. Classic dead cat diag.



You’re acting like I implied my process magically added catalyst material back in. It’s really not hard to believe what I did. We all know the s series notoriously burns oil. Car has over 200k. I went through a quart every 500 mi before rebuilding the engine. All those years of soaking the cat with oil eventually covers the metals in the honeycomb with a white ash that’s is the byproduct of the oil “baked” on due to how hot the catalyst reaction gets. Then the gasses can’t react with the metals anymore, and then no more catalyst reaction. It’s not my first time seeing the inside of a poisoned cat.



After acid wash I had a little over 100 deg difference on my inlet vs outlet temp. Rear o2 holds steady. Catalyst monitor ran and passed. I drove the car for a week before I got the smog that ultimately passed. Now, about 5 months later, the check engine light remains off.



I don’t really care if you believe me or not. What do I have to gain lying to a Saturn forum? I literally reference a research paper where they proved this works using a Mitsubishi Gallant and a Mazda 323. I was nice enough to do such a thorough write up to pass it on to the community especially since the Saturn forums are dying. I remember you from Saturn fans too, and know you’ve been around forever. But yeah dude, get off your high horse. If you don’t believe it you can just not believe it or at least ask for more info in a nice way if you’re skeptical and want to draw your own conclusions. Your rude post just wasn’t necessary. There’s always one of you on auto forums that just makes them suck. Unnecessarily rude to stroke your know it all ego when you have no idea what kind of experience the people you’re talking to have or don’t have. You can go ahead and ban me now. Have a good day.

I'm curious as to how much all of the materials you bought cost total? I'm sure it's not as much as a new cat con would have cost, but would you mind sharing? After all, it's been over 4 months and if the CEL isn't back on, I'd call that a win. When you did your rebuild, what kind of shape were the rings in and what did you replace them with, OEM or aftermarket?

No problem. I want to say I spent around $50 for the materials. The acids were found on Amazon. I had a recycle bin laying around that I ended up using to dunk the cat in. The heating element was a cheap one also found on amazon. Unless you had a nice one, I wouldn’t touch any part of the setup due to the possibility of it being live as some of the reviews suggested for those cheap heating elements. I just made sure not to touch anything until I pulled the plug on the heating element and it was fine. The baking soda I got at a smart and final which is a store that sells restaurant items in my state, so I was able to get a big tub of it.

But yeah, an aftermarket cat for my 96 Saturn was around $600 since I’m in California. Needs to be CARB legal. I was not about to buy that especially knowing it was inferior to the original cat. I knew of the research paper long before trying this, but figured now was a better time than ever to try it and it paid off. Plus it was a good feeling knowing I was able to save my original cat. They don’t make them like they used to, and I’m glad I got to keep mine original to the car.


As for the rings, the first and secondary rings looked fine from what I remember. It was the oil control rings that were shot. Seized up and stuck. I used the Sealed Power aftermarket pistons and Mahle rings. I bored the cylinders out 0.10”. Was very worth it. The car is fun to drive and I don’t burn a drop of oil now.

Interesting post.

Initially I wasn't going to respond, but there's a lot of anger in that there post, so I thought it was only right to respond.

If you review my answer carefully, as I just did, you'll notice that most of my comments centered around not being able to rejuvenate the catalyst. However, your post was about rejuvenating the catcon, not the catalyst. There is actually a statement towards the end to the effect of you may have rejuvenated the catcon but I don't think you've done diddly to the catalyst itself.

Quite a bit of BS has flown on this and every forum over the years concerning everything from tuning without flashing the PCM and without a standalone controller, to increasing horsepower with performance chips, to my personal favorite, the Turbinator, which aligns the air molecules right before they go into the throttle body causing less air friction and more smooth and complete combustion in the cylinders.

For whatever reason, others feel compelled to post fake scenarios that supposedly apply to their car, then get hot and bothered when I or someone else with much more knowledge and experience calls their bluff on the first or second post.
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Although I failed to address your statement properly, at the end of my response, I pointed out the information that any scientist or chemical engineer would want to see in order to fully believe the data supplied or lack thereof.

Why do I think this way? Because I'm a scientist. Specifically, an analytical chemist. So you don't know my experience with catalysis, reactions, etc. either, do you?

I was hoping you could provide data to fill in the gaps I mentioned, but that did not occur. To sure up your hypothesis so that anyone looking at the situation would have all the information they need to confirm that it is what it looks like.

On this forum, when "I call bs" is tossed over the fence by me personally, it means that I'm inviting whoever posted what they posted to prove it. That takes different forms in different situations. And your situation, you didn't set out to document this in the way a scientist would. And that's totally fine. I was just hoping there was more there to make your story more convincing. But you never returned.

Did I beat on you when you were gone? Nope.

So in the end, my response to your post was misaligned with respect to what your effort was trying to demonstrate, but in the end, I did address and agree that you may have rejuvenated the catcon.

So I'm going to go edit my previous post, because when I'm wrong I admit it. I was wrong. So I'm going to go fix it.

I just don't understand why my acceptance of your efforts is so important to you.

I'm just another guy with an s car.......

Well, I have a very limited knowledge of chemistry and how things work. I never took it in high school or college because I just wasn't interested. Girls and beer were my interests back in those days! Anyway, chemical cleaning of things does work on a lot of different items, so I'm not going to discount it when it seems possible to me. I figured the oil control rings were in bad shape due to the fact of how much oil you said you were using. I think you made a good choice in the parts that you chose and boring it .010 over should have given you just a slight bump in hp. Have fun with it and be careful racing along the interstates in CA. I have cousins all over the state and want them to be safe. LOL If I ever foul a cat con, I MIGHT try your solution.

Really? This is so obvious that you’re dancing around that you were just rude and didn’t need to be. You came at me like I came to defend my dissertation on materials science with my initial post.

Being a scientist doesn’t excuse being rude. I’m an electrical engineer, and prior to that I was an automotive technician with a good deal of experience. I don’t talk to people the way you did. But I’m in the stem field too so should I be going around acting like you to people? Does that excuse it all now?

Again, you could have came with all the skepticism you wanted to. You could ask if I had o2 data, ask whatever you wanted about it, and you wouldn’t have gotten my “anger fuel post” acting like you have no idea why you got such a response. Instead you just ripped into me assuming (ironically) that I did nothing to my cat and had nothing to base it on without knowing I properly diagnosed my issue through scan data. Sorry I didn’t get out my lab coat when doing so. Like you know…having a life, needing my car to pass smog, not starting all of this to do some research case study with initial intention of posting it to car forums. I did it because I already knew of the research paper and figured now was the time to try it so I could save myself some money. And again…the research paper exists. You wanna get all scientific for your jollies? Go read that. That’s better than any “my friend says this adds 300hp” bs informal forum post on any site out there. I mean I even reference the paper in the original post by its title. So you really don’t have a leg to stand on. Even if you didn’t believe me because I don’t have scan data for you, that paper sure has all the data you’d want to see.

Let’s put it like this. We both remember OldNuc. We both know he was an accredited nuclear engineer with some rare credentials. I’ve never once seen him act anywhere near the way you did in your initial response. He was the kindest guy, even if it came down to walking someone through changing a battery. Was he not a scientist because he didn’t rip into someone for not checking the specific gravity of the electrolyte in the battery to use the scientific process to condemn it? Or not being mindful enough to take pictures of the hydrometer for us so we know he’s not lying if he says he did? Your reasoning for your reply is ridiculous. I’m not contributing or want to be a part of your forum. Besides, I've got junior engineers to rip into for using ohms law without using axioms to prove multiplication actually works the way they say it does before using it. You know, being a scientist. Inspiring others.

Be better.

Thanks man, I put a lot of love into it just because I don’t like seeing old cars go to the crusher. Special place in my heart and all that. Also, nothing wrong with girls or beer lol. Yeah the extra bump in hp is noticeable and it’s a peppy little car. Wish we could still buy the manual trans overhaul kits. Still works fine but she’s got some miles on her. Junkyard trans it is for us now, but we manage. I can proudly say I don’t drive it like a maniac, but yes I do love opening it up on an empty highway. Anyways, thanks for considering my repair if you ever needed to. Cool to know someone appreciated it.