Restoring old catalytic converter's efficiency (cleaning method)

[California98Civic]

Originally Posted by jimmylomax

... do you think the times the code came back may have been longer stints without EOC? I ask because sometime this summer, I got a P0420 in the Fit on a long commute where I left the AC running for a passenger. I cleared it and it has since come back a couple times when I went longer than about 15m between EOCs.

I don't think it was the EOC as much as perhaps burning a little oil through the valve guides and/or oil control rings. In EOC maybe the leakage does not have as severe an affect on the CAT's efficiency as when the engine goes constantly for 30 mins and more. My second recurrance was under high load climbing a mountain pass into the high desert, so... pretty hot and probably oil burning?

Originally Posted by jimmylomax

Did you run an OBDII scanner and look at the O2 sensor data or measure pre and post cat temperatures? (I've got 30 days to make mine happy to pass my local DOT inspection).

My 1998 Honda has no CAT temp sensors. Wish it did. Some things remain a mystery to me...

You are going to "boil your CAT in acid?"

[jimmylomax]

Originally Posted by California98Civic

I don't think it was the EOC as much as perhaps burning a little oil through the valve guides and/or oil control rings. In EOC maybe the leakage does not have as severe an affect on the CAT's efficiency as when the engine goes constantly for 30 mins and more. My second recurrance was under high load climbing a mountain pass into the high desert, so... pretty hot and probably oil burning?



My 1998 Honda has no CAT temp sensors. Wish it did. Some things remain a mystery to me...

You are going to "boil your CAT in acid?"

I'm not doubting or questioning the source of the cat efficiency losses. I guess I'm questioning the detection. I am wondering if the reason mine hasn't been throwing P0420 is because it takes at least 15 minutes of running without an engine restart for the OBD diagnostic to perform and fail the test before throwing the trouble code. I threw my OBDII scanner on yesterday and graphed my downsteam O2 and it seems clear to me I do in fact need to give whiskers a bath of acid. Here is a plot at steady load and speed at 60mph showing my downstream O2 all over the place (which I believe in indicate of a poorly functioning catalytic converter... EricMyCarguy indicated it should hold flat at 0.5v meaning o2 inside and outside exhaust is 1:1)

RE: measuring exhaust temp, I don't think most cars have that sensor - I meant with an infrared handheld gun.

[California98Civic]

Originally Posted by jimmylomax

I'm not doubting or questioning the source of the cat efficiency losses. I guess I'm questioning the detection. I am wondering if the reason mine hasn't been throwing P0420 is because it takes at least 15 minutes of running without an engine restart for the OBD diagnostic to perform and fail the test before throwing the trouble code. I threw my OBDII scanner on yesterday and graphed my downsteam O2 and it seems clear to me I do in fact need to give whiskers a bath of acid. Here is a plot at steady load and speed at 60mph showing my downstream O2 all over the place (which I believe in indicate of a poorly functioning catalytic converter... EricMyCarguy indicated it should hold flat at 0.5v meaning o2 inside and outside exhaust is 1:1)

RE: measuring exhaust temp, I don't think most cars have that sensor - I meant with an infrared handheld gun.

I think these are pretty interesting points and I think I will put the downstream O2 disply onto my UltraGauge on the dashboard. I am pretty sure mine jumps around too. But I am not surprised, since the car passess smog but is not as clean as new. Clearly, my unit is within tolerances tho not optimal.

My moments when the CEL has returned, and generally whenever it showed up, were NOT during EOC. They were after significant stretches of steady throttle. I do more of that in recent years on freeways than once upon a time because I have a 0.710 fifth, 3.25 FD, 15" rims (12 lbs), and 175/70-r15 tires... so it cruises flat ground getting remarkable FE... not much benefit to EOC in such conditions.

[oil pan 4]

With palladium prices near $2,300 per ounce and platinum back up around $1,000 I support this.

[California98Civic]

Originally Posted by oil pan 4

With palladium prices near $2,300 per ounce and platinum back up around $1,000 I support this.

Right?! I am still running the OEM 1998 CAT and legitimately passing CA smog testing with much room to spare. I have spent maybe $50 to acid wash the thing twice in 4 years. 274,000 miles of exhaust through this CAT. I'm pretty pleased.

[jimmylomax]

I'm happy to report another positive data point toward the project! I'll be returning to my local inspection shop tomorrow morning to get my inspection paperwork. I essentially followed the protocol outlined in this thread.

A couple points to hopefully help clarify or append to the discussion:

I bought an 8oz package of oxalic acid from Amazon for $9. It was just barely enough for my 30 qt turkey fryer pot purchased from Craigslist. (I mixed with 7 gallons of water... 8oz oxalic acid crystals was right at 350mL). I bought two pounds of citric acid as it was only a few pennies more for a larger size and apparently it has all sorts of household uses which may have various benefits over premixed products. I was going to buy a fuel pump and circulate the fluid through converter, but didn't. If I have to do it again I think I will. I just threw the pot on the grill which worked very well and made it easy to control the temperature (it takes a long time for 7 gallons of water to drastically change temp).

So, had everything gone right, I'd have been in about $40.

....unfortunately...

one of the shoulder bolts fixing the cat inlet to the exhaust manifold collector outlet stripped on the way out. I've never seen this one before. I had the impact straight on it and had to fight it the whole way toggling between forward and reverse after heating the weldnut a couple times with the map gas torch. It appears material from the bolt threads was left deposited in the nut. Hindsight being what it is, I guess I should have done the 'ol wax on the hot threads trick. After getting the $30 fastener from local Honda dealer and tapping the weldnut threads, we got back on track.

Of course I sort of left out the part about how when I tried to find the thread pitch against the other bolt I incorrectly thought it to be the larger M9x1.25 which I had a helluva time threading into the M8x1.25 welnut on the car all upside-down like reaching through the subframe... so wanting to be sure not to screw it up worse, I elected to pull the exhaust manifold (plus I'd noticed a little valvetrain noise lately and wanted to check valve clearances anyway).

Attached is an updated downstream O2 sensor graph. I sure wish they unlocked the upstream sensor for general use. It clearly is much more steady, but maybe not as much as I had expected. That being said, I've only had two 25 mile runs and it clearly continuously improved throughout my first run this morning. I got the happy green "Complete" for Catalyst after only about 10 miles. Side note, it appears one may not be able to pass the Evaporative system diagnostic if not first passing the Catalyst test. That one cleared on my way home this afternoon (the next drive cycle).

Also, I did find an exhaust temp sensor on my car "Cat B1S1" and added that to my display. I guess this is measured by the upstream O2 sensor; without a sensor just downstream of the CAT it doesn't seem too helpful to aid in detecting a poorly performing cat. I found some interesting notes here: https://www.aa1car.com/library/converter.htm " In many late-model engines with multipoint fuel injection, combustion is so clean that the converter has little to do and the difference between the inlet and outlet temperature may only be 30 degrees F at 2,500 rpm - which is a lot less than the old rule of thumb that says a good converter should show at least a 100 degree F difference fore and aft at cruise."

Value of answering the neighbor kids (while wearing goggles, gloves, and high-end mask and dipping the assembly into the pot on the grill), "it's a vat of acid" [which I'm using to save hundreds of dollars while hopefully learning a thing or two] and then cooking dinner next to it... Priceless (unless I get cancer, of course.).

[California98Civic]

I'm really glad it works for you, and thanks for adding data to the thread for others to see. What does "heated catalyst" mean? Is that an electrically heated pre-CAT kinda deal like some manufactures have experimented with?

(And, nothing quite says "committed to economy" like making your dinner on the same flame as you cook the CAT. Nice!)

[jimmylomax]

Originally Posted by California98Civic

What does "heated catalyst" mean? Is that an electrically heated pre-CAT kinda deal like some manufactures have experimented with?

Must be. That panel is the standard OBD2 diagnostic screen for all vehicles. In the state of Missouri you cannot pass inspection with more than one "Incomplete" (for my model year).

I noticed in my Haynes manual they went to two catalytic converters on the Fit in 2009. I believe this is the more common approach of getting into closed-loop mode as quickly as possible.

"In 1995, [] an electrically heated catalyst [] was used in [] the BMW 750i. Heating coils inside the catalytic converter assemblies are electrified just after the engine is started, bringing the catalyst up to operating temperature very quickly to qualify the vehicle for low emission vehicle (LEV) designation. BMW later introduced the same heated catalyst []

Some vehicles contain a pre-cat, a small catalytic converter upstream of the main catalytic converter which heats up faster on vehicle start up, reducing the emissions associated with cold starts. A pre-cat is most commonly used by an auto manufacturer when trying to attain the Ultra Low Emissions Vehicle (ULEV) rating, such as on the Toyota MR2 Roadster." https://en.wikipedia.org/wiki/Cataly...Warm-up_period

[California98Civic]

Except under extreme heat and mountain climbing conditions last summer, the P0420 CAT failutre code has not come back. I have received my biannual SMOG test notification from California DOT, and I am going to take the car in soon. It'll make a good test of the longterm effectiveness of the cleaning. Although I did seafoam spray the engine through the throttlebody and thoroughly recondition the PCV (which had become badly gummed and stuck partly open), the emissions stuff is all the same. I am hoping for even better numbers than 2018.

[Xist]

Originally Posted by oil pan 4

Platinum broke $1,000ozt the other day and palladium isn't too far behind.
So I say clean those cats.
If those prices go much higher we are going to start having problems with converter theft again.

What do you know?!

California98Civic, did your acid-distributing habits ever catch up with you?