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Some people have suggested that I remove my cars catalytic converter. This is because my car is designed for a different market, and the manufacturer recommended fuel is not sold in my area. It is common for cars here to have the cat get clogged and the only options are to either install a new one, which is expensive, or to completely remove the cat, which is not a legal requirement here. Are there any complications which could arise due to removing the cat, apart from the composition of the exhaust fumes?

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    This question has a "just because you can doesn't mean you should" quality to it – Zaid Aug 13 '16 at 18:46
  • Please post the make and model of vehicle please. – Moab Aug 13 '16 at 20:15
  • Suzuki Hustler (JDM Kei Car) – Herge1 Aug 13 '16 at 23:41
  • What kind of car? And are your O2 sensors directly in your cats? – TRIGGA Aug 14 '16 at 13:38
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    Where is "your area" ? Unless the available fuel is leaded, it will not degrade the catalyst. – SteveRacer Aug 16 '16 at 2:59
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tl dr: There would be no issues with the running of the vehicle.

If the car in question is equipped with OBDII (or the international like), where the cat is being monitored by a second lambda sensor (O2 sensor), the only side effect of removing the cat would be the check engine light (CEL) would illuminate to show the secondary lambda issue. This would be more of an annoyance than a problem, but it will remain lit all the time. This would preclude you from seeing it light if a real problem occurred. The only way around this would be to put in a replacement for the lambda sensor which would fool the computer into thinking everything was okay (there is a term for these fake sensors, but the name eludes me at present), or to have an aftermarket tune put into the computer, which would set the thresholds for "out of range" on the lambda sensor so the CEL would never illuminate.

  • I have been told the same by a bunch of other people. Thank-you for the reply. – Herge1 Aug 13 '16 at 18:33
  • That or modify (flash) the obd2 software to ignore the cat monitor. – Moab Aug 13 '16 at 20:18
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    I believe the term that eluded you is a 'non-fouler' mounting bracket, which is basically a spacer that threads in between the existing secondary o2 sensor, and existing secondary o2 sensor hole. It serves to remove the sensor from the flow of exhaust air such that only a little exhaust gas reaches the sensor, fooling it into thinking the cat is still removing the necessary gasses. – MooseLucifer Aug 16 '16 at 13:13
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Is it a good idea?

To address the literal question in the title, no. Just because one can doesn't mean one should.

  • Not for the environment

    The cats are there to scrub out the most of the CO and NOx nastiness that is the byproduct of internal combustion. If I remember well, these chemicals contribute to acid rain.

  • Not for your health

    There's a pretty good chance the fumes will find their way into the vehicle cabin, especially if your windows are rolled down and/or you have an exhaust leak. These fumes don't just smell bad - they can induce headaches as well.

  • "There's a pretty good chance the fumes will find their way into the vehicle cabin, especially if your exhaust header gaskets are shot." why is this possible just because you remove the cat? – Moab Aug 13 '16 at 21:57
  • @Moab I've not experienced it myself but have read forum posts of others who decat and then complain about an unbearable stench in the cabin, even with the windows rolled up. I do agree with you that maybe a bad gasket isn't the right source for such a leak; I'll update my answer to reflect it – Zaid Aug 13 '16 at 22:36
  • Most Forum posts should be taken with a grain of salt, except for this site.....I have done it on hundreds of vehicles without issue. Fixin to do it on my 89 accord.... – Moab Aug 13 '16 at 23:30
  • There is just no way fumes will get into the without the windows being rolled down. The cat will be replaced with welded on piping, so the only outlet is going to be the tailpipe. As for the environment, yes, the cat does remove the gases which contribute to acid rain. However, the fuel in my area has impurities in it which commonly cause catalytic converters to malfunction after as little as 30,000 Km. It would be too expensive to replace it on such a regular basis. – Herge1 Aug 14 '16 at 0:18
  • @Zaid I have also read a lot about 'rotten' exhaust smell after test/resonator pipe installs, though I've never tried it myself. Having said that, my 3.5 v6 and your 5.0 v8 are in much different leagues than (eachother, and) the little engine in a Suzuki kei car. I ran my little 1.5 Civic without a cat for years and (brapbrapbrap) didn't smell a thing. – MooseLucifer Aug 16 '16 at 15:07
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The other answers have addressed the environmental and health concerns, however, I want to add a few points.

Firstly, if the specified fuel is not used, this can cause more problems than just a damaged catalytic converter. You should address this as a separate issue. Most manufacturers will specify a minimum requirement and recommended standard - don't confuse the two. Read about the different rating standards here: Octane Rating wiki.

Secondly, Find out whether your fuel stations use RON, MON or AKI ratings. If you are unable to use the recommended spec but can use the minimum spec, then there should be no harm to your catalytic converter.

This assumes that your fuel suppliers and fuel stations adhere to these standards. I know some parts of the world don't have good standard enforcement and fuel can be mixed with water or other contaminants. This is a separate issue, so please update the question if needed.

Thirdly, removing the catalytic converter may trigger a fault code which will illuminate the check engine light (assuming you have one). You can get around this by fitting a spacer on the downstream lambda (O2) sensor. This way you will have a normally functioning check engine light should you have any actual faults.

Finally, I would leave the catalytic converter in place until you are certain it is damaged. I would only remove it if it becomes clogged/blocked causing performance issues. In that situation, replace it with a free flowing silencer box / resonator / muffler. If you replace it with a straight pipe it may make the engine sound become undesirable. Make sure this is done properly with proper flanges and gaskets to prevent the exhaust blowing.

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    +1 for addressing the underlying problem of the fuel issue. – Jason C Aug 16 '16 at 15:40
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Removing the catalytic converter will save alot more money than replacing it and will make your engine exhale better and last longer due to the removal of a suffocation device "cat" only issue outta all the ones I've removed it is if the downstream O2 sensor is plugged directly in it, which there are ways around. If that is the case then the first option is-remove the "cat" gut it out completely, reinstall it, and plug the sensor back in. Option two- remove the "cat" fill in that gap with exhaust tubing, bore a hole in the new pipe that the O2 sensor will fit snuggly in and there should be no engine light as long as that sensor has hot gas exhaust flowing over it it's not gonna trigger an error code to the cars computer. If there's no sensor in the cat just chop it off and fill in the gap. It's gonna run alot better I'll tell you that. I do it to every car I've ever had and ever will have.

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    The P0420 Check Engine Light is triggered by a reduction in catalytic converter efficiency. Kitty go bye-bye means P0420 will be on constantly, because a cat that isn't there isn't very efficient. "Hot gas flowing over it" doesn't suppress the check engine light. The secondary needs to be richer when the primary is lean, and leaner when the primary is rich, as well as a certain number of transitions and response time, in order for the catalyst to be deemed sufficient "efficiency". – SteveRacer Aug 16 '16 at 2:52
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A catalytic converter makes no use if short distances are run, Like in my town. When he is hot, he cleans well. Problems with a catalytic converter can occur when exhaust-gas is rich in fuel becouse of faulty fuel injection, And/or sensors are broken, it can melt down, and clog exhaust system.

  • Welcome to the site. I'm not quite sure how this answers the question? Maybe you'd like to add more detail into it so it will attempt to convey information about what the OP has asked? – Pᴀᴜʟsᴛᴇʀ2 Aug 6 '17 at 9:52
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In places where smog is not a problem, the catalytic converter does more damage than good. It reduces the efficiency of the vehicle, forcing the consumption of more fuel than would otherwise be burnt. In this context the answer is YES.

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    This comment is absolute horsefeathers. Do you have any citations or references for this missive? A catalyst only "consumes" fuel that didn't oxidize in the engine. In fact, a careful watch on the Air Fuel Ratio is a key component in making modern vehicles as efficient as they are. Please do some research before you issue opinion as fact. – SteveRacer Aug 16 '16 at 2:57
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    @SteveRacers Maybe the point would be that a cat increases backpressure? – I have no idea what I'm doing Aug 16 '16 at 12:27
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    @IhavenoideawhatI'mdoing That's not what the comment says. And the "science" explanation is bogus no matter what. – SteveRacer Aug 16 '16 at 13:56

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