Chemistry of catalytic converter cleaning?

[sk_pete]

silicates in the antifreeze that poison the cat (and the oxygen sensor).

in what shape the engine is, if we need to consider this...

 

[sk_pete]

citric acid

very good chelating agent, hardwater residue remover

 

[d00df00d]

What effect are you trying to get, and what issue are you trying to resolve?

So here's why I'm looking at this but not urgently:

1. Car has >140k miles on it
2. Has consumed oil since I got it >60k miles ago, though I can't tell how much was from leaks (just fixed) vs. burning
3. Occasionally throws ghost codes (no CEL) for cat efficiency; I'm pretty sure those have always been O2 sensor related, but it's never possible to say 100%

So, no signs of current or imminent failure; just enough reason to start worrying about potential cat poisoning.

This thread alleges good results from a procedure based somewhat on a paper from 2006. Supposedly dilute oxalic or citric acid can un-poison a cat and mitigate some of the other potential effects of catalyst aging. It's a simple enough procedure that I might want to do it preventatively next time I have that part of the exhaust off the car. But of course that paper is only one source and I don't know how to assess its credibility, so I was hoping for some more input. Also, the paper does say they kept the solution dilute so as not to damage the washcoat... which suggests to me that if I get something wrong, I might damage the washcoat. That's why I'm interested in the discussion about chemistry.

If you already drive it like an M3, I don't think there is much else you can do. I don't know about that generation of BMW, but, many cars I see only monitor the front cat's efficiency, so you may only need to replace 2 of the 4 if there is an issue. I seem to recall that those engines use oil, so the cats may just become less effective over time.

You're right: if there were a problem with passing emissions or something, only the primaries would have to be changed. Still expensive though.

Also, I want your car. I test drove a CPO '08 M3 6MT Sedan in 2010 as a potential replacement for my '06 6MT G35 Sedan, which already had over 100K miles on it. I immediately fell in love with the engine/transmission combo, but I was concerned about operating costs while driving the miles per year that I was doing. Shortly thereafter, I dropped to a more reasonable driving schedule and bought a 3rd car, so the M3 probably would have been fine as my garage queen. I've always kind of regretted that decision. On the other hand, the G35 is still fun and fairly inexpensive to over maintain. But that 8,300 rpm V8...

 

[el Nuke]

FWIW - I just utilized the dawn trick on a Nissan rogue cat (pretty sure the cat itself is a Dorman aftermarket unit) as a last ditch, “can’t hurt…”, type solution to a P0420, and it actually worked…for now anyway.

Just need it to stay gone long enough for the owner to get an inspection and stop asking me to fix it. And I believe it will do that, so color me surprised, but nonetheless convinced the Dawn trick has some merit.

Speaking of convinced, I’m utterly convinced the P0420 will come back at some point and the cat will have to be replaced at that point to turn off the CEL. But that will be the problem of whoever buys it from the owner (car lot), so doesn’t matter to me.

 

[Slow Car Sport Mode]

FWIW - I just utilized the dawn trick on a Nissan rogue cat (pretty sure the cat itself is a Dorman aftermarket unit) as a last ditch, “can’t hurt…”, type solution to a P0420, and it actually worked…for now anyway.

Just need it to stay gone long enough for the owner to get an inspection and stop asking me to fix it. And I believe it will do that, so color me surprised, but nonetheless convinced the Dawn trick has some merit.

Speaking of convinced, I’m utterly convinced the P0420 will come back at some point and the cat will have to be replaced at that point to turn off the CEL. But that will be the problem of whoever buys it from the owner (car lot), so doesn’t matter to me.

Just to clarify "The Dawn Trick." You're talking about pulling the 02 sensor out and tubing in some heavy concentration of Dawn, maybe straight Dawn maybe small amount of water as a carrier? Then start run and let monitor set? I've seen this.. if you can easy get 02 sensor out, could be viable.

Correct me if I am wrong but P0420 can set with the converter operating at 95% efficiency.. it seems sometimes they can be "cleaned" and sometimes not, perhaps Italian Tune-Up your best shot, I think @DriveHard post says the best shot at success because if that doesn't do it, either chemicals or nothing will:

After properly warming your car, run at 3/4-4/5 of your redline at highway speeds (shift to appropriate lower gear as to not exceed speed limit) for 5 miles followed by 5 runs full throttle to redline at a lower gear, coasting back down each time, then 5 more steady miles at high engine RPM's, then 5 miles in top gear (slow engine speed) at a steady 60 mph to cool everything down.

 

[el Nuke]

Just to clarify "The Dawn Trick." You're talking about pulling the 02 sensor out and tubing in some heavy concentration of Dawn, maybe straight Dawn maybe small amount of water as a carrier? Then start run and let monitor set? I've seen this.. if you can easy get 02 sensor out, could be viable.

Correct me if I am wrong but P0420 can set with the converter operating at 95% efficiency.. it seems sometimes they can be "cleaned" and sometimes not, perhaps Italian Tune-Up your best shot, I think @DriveHard post says the best shot at success because if that doesn't do it, either chemicals or nothing will:

In the case of that Rogue, the cat is a part of the exhaust manifold coming off the front of the engine, so I removed the whole piece and submerged it in a bucket of soapy water, agitated, rinse, repeat several times over the course of a couple days. For most other cats that I’ve seen on cars, where it’s less accessible and much harder to remove and install, this trick would not be feasible.

Also, as it turned out, the P0420 code ended up coming back after a couple weeks, so I ended up replacing it after all.