Hondacommuter

Have a 2003 Honda Accord EX with the 3.0 V6 and six speed manual. Warm up catalytic converter failed on the front bank (radiator side) and plugged up the exhaust at the final cat downstream of the Y pipe. The warm up cat on the rear bank (firewall side is intact with the honeycomb material tight and open.) I had gotten a 0420 code about lost efficiency on the front cat a few days earlier and I was waiting for the new cat to arrive. My daughter was driving to a meeting and the car lost power and quit. I dropped the exhaust and removed all the cats and boy what a mess. Before I purchase any other parts what are the chances of engine damage due to the back pressure caused by the plugged up cats. I have two concerns. Burnt valves in the front bank and possible backup of cat material into the exhaust valves, This is the first vehicle I have had with warm up cats acting as the exhaust manifolds,

user456101

Might be good to watch some YouTube videos by Scotty Kilmer and Eric the Car Guy about cleaning clogged catalytic converters yourself. If there are holes in things or they were damaged in the removal process and can't be put back on, then of course disregard this advice. You will get P0420 code whenever a Cat is less than 95% efficient so even though you get the code it may not be even close to completely clogged. If it gets really clogged usually you stop being able to go faster than a certain speed and the engine temperature gauge goes up some. If the engine can't breath out, then it can't get enough air in to create enough power to go fast. The fact that it lost power and quit may be indicative of another problem like a fuel pump or clogged fuel filter. You can test the fuel pressure at the rail to see if you have good fuel pressure after you put it back together. Scotty Kilmer has a video on testing your fuel pressure. The fuel pump and filter are both together. The filter is inside the pump which is mounted in the fuel tank by the way. You can run a car without the cat without it ruining your engine but it will drive the computer crazy since all engines are controlled by computers these days. The computer is expecting feedback from the O2 sensor, and also some back pressure from the Cat in adjusting the fuel air ratio. It shouldn't affect the timing of the valves opening and closing or the travel/seating of valves themselves, so I would guess you have suffered no engine damage. If it found a way to grossly overheat the exhaust valves maybe. The only reasonable thing to do in my mind is put it back together with cleaned cat, or with a new one and see. When I checked alldatadiy.com on my 2007 4-cyl Accord it only shows one catalytic converter so I can't help more than that. If you had a clogged catalytic converter it is an indication of another problem - an engine that is burning oil, or poor spark or bad gas or something else. So, really sorry to say this, you still have a problem to find once you get a good cat back on it. You should check the spark plugs and the oil level and basically do a tune-up to see if you find what is causing so much extra stuff to come out of the engine that it is clogging up the cat so you can avoid causing the new/clean cat to clog up again.

Xist

Did you intentionally choose two mechanics that regularly contradict each other? Eric is quiet and methodical. Scotty is loud and crazy. In "Fixing Bad Catalytic Converters With Inefficiency Code P0420," Scotty recommends pouring a gallon of laquer thinner in half a tank of gas "Then I either tell the customer to drive the car 150 miles or so at higher speeds, or I run the engine at about 2,500 RPMs for about 30 minutes to run the cleaner through, and this can burn the impurities out of the catalytic converter and make it work again."

How does idling at 2,500 RPM for 30 minutes equate driving 150 miles at higher speeds?

Eric put one quart in a tank that was almost three quarters full and drove 170 miles. Many people threw a fit because he did not put in a gallon and he was above half a tank. If one gallon would have cleaned the cat, one quart should have shown a difference, but he did not see anything significant. Having more fuel in the tank just meant it would take longer to have effect, but he drove 170 miles, not 150.

Scotty said that if the lacquer thinner did not work, to try soaking it in soap and water. In "Cleaning Catalytic Converters With Soap and Water," at 12:36 Eric shows bubbles coming out of his muffler, but he did not see any improvement, either.

There is a discussion on Ecomodder called "Restoring old catalytic converter's efficiency (cleaning method)" where the poster shared a scientific paper stating that soaking a dirty cat in hot citric and Oxalic Acids restored efficiency. It seemed to work for him. I will give it a try when I can get my hands on the chemicals.

DCFIVER

You can very well burn the exhaust valves with a clogged cat. But it doesnt happen quickly, so there is a good chance your vehicle is ok in that regards. Additionally you CAN get cat materiall back into the exhaust by way of reversion. The issue is, that it will bypass the valves and enter the combustion chamber ,and then the engine block. If it makes it that far you will have engine damage. The catalyst material acts like sand paper and will scratch and score the cylinder walls. It was a major issue for Nissan in the early to mid 2000s.



(BTW Scotty Kilmer is literally the laughingstock of the automotive repair industry. Id steer clear of his advice. Eric the Car guy has pretty good "how-to" videos,but his knowledge on auto repair seems to stop with removing and replacing parts. I would not look to him for diagnostic advice)

Xist

Thank you for your response!

So, watch ChrisFix instead?

What would you do with a car with flood damage? Scotty says as long as you do not start it while it is still wet and the computer did not get wet, with just a tuneup you are good to go!
Eric says you will have corrosion, mold, and various other problems that will plague you until you finally get rid of the car.

Scotty also has several videos promoting stop leak products while Eric disassembled a cooling system and showed that stop leak only made everything worse.

Do you recall any specific problems with his diagnostic advice? Right now this video is most relevant to me:
This is the failing cat on my 99 Accord:

Huh. Perhaps we do not need that extreme closeup.

In that video, Eric says to get the car up to temperature, connect a bidirectional scan tool, and monitor the O2 sensors and the coolant temperature. Rev to about 2,250 RPMs and make sure the primary sensor alternates between rich and lean and the secondary to stay steady around 0.5v, then maintaining RPMs, get underneath the car, and use an infrared thermometer to make sure the outlet is 100° warmer than the inlet.

I guess the original went out a couple of years ago and the previous owner installed the cheapest one he could, an Evan Fischer, which just wore out. I have been trying to figure out why the cats have failed so that I am not worrying about installing a fourth, just a third. My car does not burn oil, but people keep telling me it does, and that is the problem.

Or they switch to super helpful mode and say "It's dead. Let it go."

DCFIVER

I dont know who that is. Im sure there are a lot of good guys on the web,I dont know them all. 2 of the ones that I know are good and work in the industry are "The Humble Mechanic" and" ScannerDanner"

If Im not mistaken,ScannerDanner was Eric-the-car guys teacher.(I could be mistaken ,though)

With that being said,I never said Eric was bad,his vidoes are very informative ,(mostly) accurate and well made.

Scotty's a moron and Eric is right.

Scotty's a moron and Eric is right.

To be blunt,hes basic. As in, he seems to have a rudimentary understanding of the intricacies of diagnostics. The cat video is a good example. Checking the outlet temperature of a cat to determine if it is good or not went away in the 70s. Dual bed, low oxygen storage capacity catalyst(Which many cars have now) do not behave the way he describe. Additionally, double wall constructed exhaust pipes will skew the readings of a temp gun.

Again R and R parts seems to be his forte. Nothing wrong with that,there a few hundred thousand mechanics in the US that make their living that way.


If you need help,make a thread.

Xist

Is his information about the bidirectional scan tool correct? The advice I found on here through the search function was the same as Eric said (including taking the temperature).

Did I miss a thread that had better information for the cat? I do not want to create a thread for something already here.