Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show



Mechanic??? Are you SERIOUS??? Does this clown look like a MECHANIC???

He is an artist of bovine excrement…

He is an artist of bovine excrement…

Much like the Car Talk brothers? He, like them, runs a talk show in Houston, and has done so for a long time. Like them. Have you actually listened to him, or checked him out?

When I got a low efficiency cat error code last year, after running 17 miles downhill near Orizaba in second gear, with the injectors shut off, I did a lot of researching on both cat failures, and this lacquer thinner stunt. I found a large number of people who said it was so obvious it would wreck the fuel system they would never try it. I also found a very small number of people who tried it and said it actually cleaned the cat converter.

In my case, after some weeks the code went away. The cat may have cleaned itself up?

There is another thread on this issue, and a man ran a gallon of unknown formulation lacquer thinner and now his sensors produce error codes. He did not say if he was sure his cat converter was bad, or just tossed in the thinner when he got the code. He experienced bad sensor codes, but we don’t know what caused that yet.

So, the first thing you need to do is eliminate a bad sensor before you even conclude you have a bad cat. Most hits I got said most cat error codes involve bad sensors, so check it out before assuming it is a bad cat.

Let me explain what they do. The engine computer compares the readings of the sensor BEFORE the cat to the sensor AFTER the cat, when the car is warmed up. The extremely expensive rare earth screen in the cat when it is hot burns any residual materials so the output sensor should read much cleaner then the input sensor if it is working properly. If it does not, the engine computer enables the low efficiency cat error code, which does not prove the cat is bad.

If one of the sensors is bad, you can get a bad reading which can cause the computer to declare the cat bad, when it is actually a bad sensor.

And,that seems to be much more common than a bad cat, as far as I can glean from Google.

So, first check out the sensors, if you can’t try to find a good mechanic who can. Until you have eliminated a sensor failure, you cannot be sure there is a bad cat at all.

Well, it’s definitely a real problem, my gas mileage has slowly been deteriorating. It’s about 4-5 MPG’s less than I usually get.

I replaced the 02 sensor on the upstream and I’m still getting the code. I’m quite sure my cat is stuffed up.(were at 253k miles) Before I bought it there was a leak in the exhaust manifold and it caused a lot of back pressure. The gasket was so black when we replaced it, barely any material was left on the thing… This probably did a number to the cat.

So right now I’m at trying to clean it without having to remove the cat(Seafoam). I’d remove it myself if I had a car lift, but I don’t and I’m not about to jack this thing up. I’m wondering if some sea foam into the intake of my throttle body would clean the cat or perhaps pouring it down my exhaust pipe on a steep slope and letting the sea foam do the job. Surely the exhaust pressure wouldn’t allow any sea foam to get up anywhere and do any damage.

I’d really like the latter idea to work. Thoughts?

If 'Sea Foam" is a “petroleum distillate” it will burn in the combustion chamber and it is very unlikely any will reach the CAT…No additive product will unplug a ruined converter…

Backpressure can be checked by removing the front oxygen sensor and replacing it with a pressure gauge. A simple test…otherwise you are just blowing smoke up your own exhaust pipe…

We’ve had threads on this already. Long ones. IMHO this approach is foolhearty, and putting laquer thinner into your gas tank where it might attach polymer parts in the pump and the fuel system, create a residue-maling sludge out of any sediment, leave its own sediment (anyone know how pure laquer thinner is?)…and that’s before it even gets into your cylinders and subjected to combustion…is risky and foolish.

However, let’s assume that it doesn’t attack plastic parts in your fuel pump or fuel system, and successfully combusts at a detonation rate acceptable to your engine (doesn’t cause preignition or fail to burn fully), and leaves no residue in the combustion chamber. And let’s assume that it does not cause washing down of the film of oil that your oil rings are designed to leave for your compression rings to slide on. How can you be sure that the byproducts of its combustion won’t leave residue on the catalyst, mkaing the converter even worse?

In summary:

  1. to the best of my knowledge, there are no standards for purity for lacquer thinner. You don;t know what you’re putting in
  2. to the best of my knowledge there are no combustion standards for lacquer thinner. It’s probably “all over the map” in how readily it detonates…if it detonates
  3. it probably washes off the oil film that your oil rings are designed to leave for the compression rings to ride on. It may well shorten your engine life.

If you’r comfortable with taking these risk, try it.

I think I’ll use some sea foam and pour it down the 02 sensor port in my exhaust manifold.

Do it outside…Have a camera ready…This could be one of those U-tube moments…

I want to see it on YouTube as well.

I see that you started another thread on this. If you had a P0420, why did you replace the upstream O2 sensor?

“Before I bought it there was a leak in the exhaust manifold and it caused a lot of back pressure.”

Could someone please explain how a leak can cause back pressure? Please?

I’d like to see that explained as well.

Honda, I don’t like the road this process is leading down. Seafoam is not made to be used in that manner.What it will do if poured directly onto the core in the catalytic converter is untested. It may just leave a volatile mix in your converter with emough plug to lalow it to heat up and go BOOM. Best case, it’s just going to make a mess and cause severely reduced flow in the converter core. It might even adversely affect the bond between the platinum-palladium catalyst and the cermaic substrate. Which would mean your converter insides would deteriorate.

A leak in the exhaust won’t cause excessive back pressure The pressure inside the pipe is higher than the pressure outside the pipe, so basically any leak would relieve pressure in the pipe by allowing it to escape. What it can cause is a false air/fuel reading at the oxygen sensor, causing the engine to run rich and produce excess carbon. The black stuff. And yes, that will cause th cat converter to fail and the CEL.

My recommendation is to buy a direct fit OEM replacement converter and just change it. It sounds like it’s been carboned up.

Well, I poured 12oz down the exhaust manifold 02 port and it did what I expected it to. It smoked a lot. I drove it 12 miles to work it smoked for awhile and then just up the inclines and I drove it back, hit a slight incline and it started smoking again.

I don’t know how sea foam could damage any catalyst, the platinum-palladium would probably just catalyze it. Petroleum is a very weak chemical compared to that of platinum and palladium.

Having combustibles ending up in the cat tends to overheat it. Overheating it will damage it. One of the ways cats get killed, for instance, is by running around too rich & having too much unburned fuel make its way there. The chemical nature of the combustible isn’t the only thing to worry about. But whatever. That’s what you wanted to do. You did it. Its not really a normal practice so who knows?

Well Honda you have asked for and gotten good advise on your P0420 and cat cleaning queries yet you chose to ignore them. You can not or will not explain your rational as to how a leak could cause excess pressure, and use auto products is such a way as to be useless if not harmful. Good luck in your quest for automotive knowledge and a cheap easy fix. Which by the way just may have been replace the downstream 02 sensor as said in the previous thread.

One thing to understand about catalysts is that they don’t “catalyze” anything. A catalyst by definition causes a change without itself changing.

The catalyst in your converter only seperates the oxygen from the notrogen in the Nitrogen Oxides, the NOx. The other function the converter serves is to provide an opporunity (sufficient heat) for passing carbon monoxide molecules to collect another oxygen atom, becoming CO2, and for unburned hydrocarbons to split and bond with additional oxygen atoms, forming CO2 and H2O. If there are any free hydrogen atoms, they can also bond with the now-freed oxygen atoms and form H2O.

It should also be understood that in order for the catalyst to seperate the nitrogen from the oxygen, it has to come in direct molecular contact with the molecules. Withuot that seperation, the other chemistry cannot happen. Coating the catalyst with SeaFoam won’t support that direct contact.

It’ll be interesting for me to hear the results of your experiment. My guess would be that the catalytic converter’s core has been ruined, but since it was probably ruined by the carbon coating anyway, it may not matter. Hopefully the SeaFoam won’t clog the honeycomb, and/or burn, and cause overheating of the converter.

Post back and let u sknow how you made out. I’m interested.

If my cat was really clogged and after clearing the code, wouldn’t it come back on right away if it was really clogged bad? Mine has a tendency to come on when I’m going up and down hills and 2-3 days after I clear the code.

I’m always turning right on the highway when the code comes back on. Not sure if this is a coincidence or not.

I’ve heard of people knocking the guts out of a clogged catylic converter, then just putting it back on. Not sure if doing this has any negative effects to the car or whether it is safe to do. I’d guess the stuff that comes out of the thing is quite toxic. Without a working cat, it certainly has negative effects on polluting the environment. And on emissions tests. I wouldn’t do it myself. How much does it cost for a new cat?

HondaHonda, there are still some lingering questions out there about your approach to this. First is the question of why you replaced the upstream O2 sensor in response to a P0420 code. I promise you that the downstream sensor is responsible for the code. The upstream O2 sensor puts out a wave of voltage that is dependent on the amount of oxygen in the exhaust. The exhaust then passes through the cat and, as mountainbike so elegantly explained, all of that “catalyzing” takes place. Then it hits the downstream O2 sensor and the downstream sensor is also putting out a voltage wave based on the amount of oxygen. If the catalyst is doing its job there should now be a lot less oxygen in the exhaust and the voltage variations from that downstream sensor should me much “flatter” than they were upstream. If the PCM sees too much activity form the downstream sensor - something that looks too much like the upstream it sets the code.

So, one thing that can set the code is a problem with that downstream sensor - but not the upstream one. Another thing that can cause this problem is actually just an exhaust leak - in essence an exhaust leak contaminates the exhaust gas samples.

You are also stuck on the idea that a P0420 comes from a clog. It doesn’t. If you had a clogged converter, you’d have too much back pressure and a loss of power. I’m not suggesting that the cat is either clogged or not clogged - it certainly can be anywhere in between and if there is gunk build up on the honeycomb that will keep the cat “below efficiency.” But its not a clog that does it. Its gunk that interferes with the catalyst - whether clogged or not.

What you’re saying about the times it comes on, btw, look to all be times of high exhaust production - engine load. That does suggest a cat that is marginal in its function. But you have to check it all. A tiny exhaust leak might, for example, only cause issues at that time.

I hope you got some video of your car going down the road with your smoke system going full tilt…You want emissions?? I’ll give you some emissions!! Check this out! Maybe Sea Foam will use it in a pro-mo for their product line…I mean, seeing is believing…

I figured it was the downstream sensor(I’ve had some oil and coolant leaks), I just don’t want to get under the car with a jack. I bought some ramps today and I’m going to drive it up that and check it tomorrow.

Also Bonus’s fun for me: I changed the spark plugs today and a couple had oil deposits above the washer, one was even completely drenched in oil. Looks like the valve cover gasket and o-rings need to be replaced. This car is a total nightmare and I’ve only had it for 10k miles. Here’s the list of things I replaced, tell me at what point should I just bite the bullet and get a new car? (Excluding routine maintenance items)

*New Radiator
*New Inner tie Rods
*New Distributor
*New passenger side upper ball arm joint
*Two new stabilizers
*New speedometer chip

Lots of time and frustration

I don’t know. I could probably suck out the excess oil from the spark plug wells. It certainly explains that lone wolf P0301 code I had awhile back that disappeared. I’ll just find a syringe or something and suck the oil out, the leak is pretty small so I think I can get away with watching it.

My car is also due for a timing belt change as well…