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Old 01-07-2018, 08:54 AM
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Default Cat-a-lid-it converter cleaning

Had an idea, smell the smoke?
Remove upstream o2 sensor, seal one exhaust tip, blow high pressure air into other exhaust tip.

Think it is worth a shot, maybe it will blow out some debris?
Could anything be damaged doing this?
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Old 01-07-2018, 09:29 AM
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innzane, as long as you are only using say 100 psi air, you should be good. Granted, if there are weak points in the exhaust system, you may find them and burst a hole in the piping.

Granted, here is the issue that I see, air is going to take the path of least resistance. Assuming that both cats are equally blocked, once the one clears a path, that is where all the air is going to go, leaving the other cat still plugged. You would need to only remove a single O2 sensor at a time. Even then, unless you have a very large air source (volume wise), I think you are going to find that you are going to be limited by the size of the air line you are feeding into the exhaust, resulting in less than idea clearing of the cat.

A better idea would be to get say a 3 or 4 gallon tank with a 3" butterfly valve that you can attach to the exhaust. To use the tank, you would shut the valve, let the tank press up to say 100 psi. You would then flip open the butterfly valve, sending a pulse of air down the exhaust system. This would act like a hammer and knock stuff free inside the cat. Granted, this is going to be harder on the cat (structural wise), but if you are going to blow out debris, this is going to be the way.

Another thought (can't say I have heard of people doing this), but what if you removed the upstream O2 sensor and then sprayed say carb cleaner down the hole and into the cat. That would then eat the carbon that is built up inside the cat. You can then use the compressed air to blow out the vapors so you don't explode your exhaust system on first start up.
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Old 01-13-2018, 02:40 PM
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Thx for the input. I c what you mean with the large volume air burst. I might try, I do have a tank, then try the carbon removal.
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Old 01-13-2018, 11:27 PM
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Your idea awoke the deep sleeping engineer in my distant past.

You need to consider (1) total free volume of the exhaust system (2) flow restrictions within the exhaust system, (3) Where the loosened debris, if any, will end up.

The best I could "back of the envelope" calculate, our exhaust system is about 4.2 gal total free volume (I can send you the volumetric data if you wish). This means that connecting a 4 gal air tank at 100 psi would fill up the exhaust system and equalize at approx 42 psi max pressure (If the exhaust system had no outlet and no leaks). A 5 gal supply tank @ 100 psi would result in 50 psi max, a 3 gal tank would result in about 35 psi, a 2 gal tank would give 24 psi, etc... In an open system like you are describing, the max pressure will be less, since flow restriction and the open O2 sensor hole will prevent the system from equalizing at the max pressure.

The air flow through the mufflers will naturally be restricted by the internals of the muffler. This will cause flow vortices and localized pressure drops. The exhaust resonator and pipe between the mufflers and cats will further restrict air flow. The cats themselves are honeycomb baffle chambers and will affect air flow as well. Assuming no restrictions, the max flow rate out the O2 sensor hole could initially be near 250-300 scfm and drop to 0 as the pressure is rapidly bled from the system and tank. A 4 gal supply tank @ 100 psi only holds a little over 35 cubic foot of air at atmospheric pressure. As you can see, the flow rate will drop very rapidly due to the lack of sufficient air at pressure. (Imagine cutting a 3/4" diameter hole in a truck tire and how long it takes for the tire to go flat).

Finally, consider if you want any possible garbage freed from the mufflers and exhaust pipe to be blown back into the cats. While most of the air that is introduced into the exhaust tip will exit the open O2 sensor hole, it may not have sufficient speed and volume to carry out any debris loosened. The air will have the highest volume and speed when the initial blast hits the open O2 port and then will rapidly decrease as the pressure drops in the system.

I could see a scenario where debris was freed between the cats and muffler outlet, and then catch either in the outlet of the cat, in the honeycombs of the cat, or drops on the inlet side of the cat between the engine block and the cat inlet since it may be too heavy to be carried out the O2 port due to lack of sufficient flow rate.

I don't want to rain on your parade, but I am not sure that you will get the result you are after. Just something to consider, (and a fun little exercise)......

Last edited by PanamaJag; 01-14-2018 at 01:55 AM.
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Old 01-14-2018, 08:00 AM
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PanamaJag, and I thought I overthought things. LMAO. I was keeping the volume down to something small as I am thinking the "air hammer" affect was going to be fairly rough on the cat internals. Even if you assume that the cat internals get hit with 20 psi air, there is what, 15 square inches of surface area facing the exhaust port? That would be a 300 pound force on the cat internals. Not sure what they can take, but hate to see the internals get blown "right out the O2 sensor port" (not going to happen, but you get the picture).

Gotta love when the engineering types over think things.
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Old 01-14-2018, 10:51 AM
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Someone published a thread in the forum about cleaning catalytic convertors last year. They removed them and submerged them in citric acid to remove the build up in the cats. After that they blew them out with air. The entire process at best is iffy. If i had gone to all of the time and trouble necessary to remove the cats I would just toss them and put in new ones. Air might blow out the debris, but if you have debris the cat has already failed and is coming apart. The heated precious metals in the cat is what burns the unspent fuel and once they are coated up blowing them off isn't going to restore them.
Just my opinion.
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Old 01-14-2018, 07:23 PM
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Maybe seal the exhaust outlets, blow air in lower o2 and shop vac the upper o2 hole could be a safer bet.
Muffler debris is a valid concern, blowing apart the aged mufflers is another. Yet I had the evil thought of filling the entire system with starting fluid sealing and igniting, hehe. Make a good video at least.

I will be trying soon (next 60* couple days in a row), will post if anything comes out.

I feel the same way, if the cats are out they are scrap metal. Me, just gonna buy another x-type if they are gone, way to much work.
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Old 01-14-2018, 09:08 PM
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are you getting a p420 code
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Old 01-15-2018, 04:57 PM
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I am, but misfires for an extennnnnded time are causing it. Throwing new coils and plugs on soon, last things not replaced on it. @205K the reoccurring misfires may be timing chains worn out, or cats. either will be the nail in the casket.
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Old 01-17-2018, 10:25 PM
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what codes are you getting for your misfire
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Old 01-18-2018, 09:12 AM
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I've got the same p420 code preventing the state of MD from giving me an emissions inspection. I have decided the cats need to come off after watching a youtube video where a mechanic removes a cat, cleans it with soap and water, blows it out in both directions directly with compressed air, soaks it in lacquer thinner and blows it out again and replaces it. He shows before and after cat temperatures and he shows the upstream and downstream O2 sensor outputs. No change after all that cleaning convinces me nothing I do with the cats in place will make a difference.

The ECU throws the p420 code because the downstream sensor signal is not steady. The sleeping engineer in me decided a double A battery and a couple of resistors in place of the O2 sensor output could give a very steady 0.7 volt signal. Code cleared for under $1. I'm not advocating that, just sayin' it can be done. It leads to another code (P0144?) when the ECU runs a self check on the O2 sensor but there is a long time window when the ECU will be happy enough to get you through an inspection so you can fix those cats in warmer weather.
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