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Discussion Starter #1
Ive got a problem with my much loved 06' DC 4X4. It's been throwing Catalyst Below Threshold codes for a few months now. I went ahead and replaced both Air/Fuel ration sensors and the O2's but the codes come back within 2 drive cycles. I've driven the truck repeatedly with my scanner connected, and the rear O2 sensor readings indicate that the cat's are getting tired. I removed them for a visual inspection and can't see anything wrong with them. They don't appear to have ever overheated, there are no cracks in the monolith, and I can even still read, what I believe is, a part number painted on the substrate. I've priced replacement Cat's and they're going to cost approximately 3 g's to replace. Needless to say - but I don't want to part with that much $$$ on an item that won't make my truck any faster/look better. So after a lot of research, I'm going to throw a "Hail Mary Pass" of sorts by trying 1 more option before parting with my hard earned money.
I've found research that indicates that tired Catalytic converters can be cleaned internally to remove the contaminants that caused them to fail. Scientists have performed lab tests showing that a heated bath of Oxalic/Citric Acid can effectively remove the contaminants from the Cat and not cause any damage to the Platinum/Palladium substrate. The Acid bath was shown to be able to remove over 85% of the Sulphur/Phosphorus that had poisoned the Cat, and dyno testing proved that the Cats had been successfully regenerated to nearly new efficiency levels. After reading all of the data and the procedures involved, I've decided that I will tackle this cleaning project myself " in the comfort of my own garage." My first quest was to figure out where to source Oxalic Acid. A quick internet search revealed that it is commonly refered to as "Wood Bleach", and can be purchased cheaply at any home supply/ hardware store. It comes in the form of a white powder that is mixed with water and is usually used to remove stains from wood. I then searched for Citric Acid. A quick trip to the canning section at my local Wallyworld and it was in my hands.
I performed an experiment with the acids on a smaller scale to test their effectiveness myself, before crawling under the truck and removing the cats again. I had saved the original Air/Fuel ratio and O2 sensors from my truck and used them in my own test. Both rear O2 sensors had a white-ish coating baked onto the sensor housing, where it's exposed to the exhaust stream. My thought was that this same coating may be was has caused my Cats to fail. I heated a small bowl of water on stove and mixed in a few tablespoons of both acids. I tried to keep the temp of the mixture at approximately 150*F, as that was the temp that the scientists had used in their testing. I let one O2 sensor soak in the solution for 2 hours and retained the other sensor for comparison purposes. Upon removal from the acid laced water, the differences between the two used sensors were remarkable- the coating was gone! The sensor appeared perfectly cleaned, except for the discoloration of the metal due to 115k miles of use.
I now plan to pull both Cat's from the truck and treat them to a "warm bath" some time this week end. I'm going to use the gas grill in my backyard to keep the bath warm for at least 6 hours. I'll then rinse the cats in RO/DI water and reinstall them on the truck. Since the DTC's would come back quickly after a reset, I should know whether or not this cleaning attempt will be successful in short order.
I'll report back to let you guys know if this works out or not, and I'll take/post pictures of how I performed this process for anyone that would like to try it themselves.
Wish me luck- This could save a lot of people a lot of money, if this works.:D
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

Did you use OEM or Denso O2 sensors? There's been problems with Bosch and others.

Hope it works for you! There's no way I'd part with $3k for 2 cats myself, but I'm not in SoCal and we don't have emission testing.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

Did you use OEM or Denso O2 sensors? There's been problems with Bosch and others.

Hope it works for you! There's no way I'd part with $3k for 2 cats myself, but I'm not in SoCal and we don't have emission testing.
I replaced all the sensors with OE parts a few months ago and the codes keep coming back. Up until about 5 years ago, I worked as an ASE Master Tech w/ 18 years of experience, so this is not my first go around diagnosing P0420/430 codes. It's just the first time that I've been forced to deal with the problem on my own vehicle. I've been looking into this problem with my truck for about 6 months now, and I'm fairly certain that I've ruled out any other possible causes. I've ruled out exhaust leaks (leak tested the entire exhaust system with a smoke generator) and even went so far as to disable/plug off the Secondary Air Injection system, just in case it was malfunctioning and dumping unmetered air into the exhaust (I've seen that particular failure mode in the past.)This truck had it's 90k service at 100k miles, so I know for a fact that all other sensors/components are in great shape-since I did all the work myself.
I'm only going to try the "Acid wash" on the cats, as it's the only option still available to me without going to the expense of replacing the Cats. I have to Smog Check this truck before the end of this month, so I'm really hoping this "Hail Mary Pass" will pay off.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

What a pain, at least you know what you are doing. Good job figuring this out and good luck pulling it off. It sound scary but if it works it will be an awesome finding. Good luck buddy, points sent.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

Following with interest. Points sent for forging ahead into new territory.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

I would like to thank you guys for encouraging me to move forward with this experiment. This truly is "uncharted territory" when it comes to a DIY repair. I'll have to do a search and post a link later, as I did find one thread on a Subaru Forum where one of the members did exactly what I intend to do- and it was a success. He went through all the diagnostic routines used to repair a P0420 code and it all pointed to replacing the catalytic converter. He didn't want to spend $400 on a new one ( what a deal compared to 3k ) and tried the Citric acid bath. His further posts indicated that he's been P0420 "free" for 2 years running.
I've got a 4 day weekend starting tomorrow, so I'll be "grillin' some kitties" and crossing my fingers. I'll keep you guys posted with the results.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

I wish you were able to get a real smog test to see your true emissions before and after.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

I wish you were able to get a real smog test to see your true emissions before and after.
I wish that I had enough time to document the emission levels before trying this experiment, but I can tell you this- I now work in and out of Oil refineries here in So Cal. and I have to carry a 5 gas detector for safety reasons. The detector measures H2S ( Hydrogen Sulphide ), O2, CO, LEL ( Explosive gases as a % ) and VOC's ( Volatile Organic Chemicals ) I use this meter continuously during the course of my work day, and I've noticed that it will register a CO alarm anytime that it's near the exhaust on my truck. If my Cats were working properly- high levels of CO would not be present. I won't even allow the truck to idle for any length of time because of this. I won't take any direct measurements with the detector, as it could possibly damage it, but my nose also tells me that there's something wrong with the emission levels of my truck. The exhaust of my truck had no smell to it at all when the truck was new. 116k miles later there's a definite smell and enough CO being emitted to cause a throbbing headache if you're exposed to it for a few minutes.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

well, I'm subscribed! Nothing like a good money saving trick!
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

well, I'm subscribed! Nothing like a good money saving trick!
I just finished mixing up the acid into 2 - 4 gallon jugs and I'm going to drop the Cat's within the hour. I plan on grillin' them for about 6 hours today and reinstalling them tonight. I'll drive the truck tomorrow to get on the monitors "ready" and I'll report back with my findings tomorrow.
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

i hope it works. im subscribed as well. good luck
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

This is the most intriguing DIY I've ever read here!!!
Thanks Remmy! I really hope this "Experiment" pans out. Who's ready for lunch?

 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

grilled kitties..... hehheheh
Well it's been 3 hours on the grill- time to flip "the kitties"! Some things got to be happening- the acid r/o water went in clear, and came back out with a strong "green tint" to it. I really hope that's caused by the contaminants boiling off and not what platinum/ palladium looks like when it's suspended in acid! LOL
 

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re: P0420 / P0430 and a "Hail Mary Pass" (the "cat washing" thread)

I let the Cats stay on the grill for a full six hours, so now its time to rinse them out and throw'em back under the truck. From what I'm able to see, the white coating that was baked on to the substrate is now gone. The Catalyst appears clean with a "gun metal gray" color. A couple of stops and starts later tonight and I should know whether or not this is a viable repair. Wish me luck!
 
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