POPULAR BUT WRONG

On ‘popular but wrong’, I will be bringing you a few popular opinions on car tech with explanations why they are wrong.
Catalytic converter
Catalytic converter
Indomie noodles
On this side of the globe, the catalytic converter has gained a very popular alias - ‘the Indomie’, after Indomie noodles because of the noodles like shape of the converter metals. In other worlds, it is simply called the ‘Cat’.

Cat with sensors
There is a popular believe and claim that the Cat/Indomie improves fuel economy, I.e. reduces fuel economy.  I say a big Wrong to that. The Cat is not designed to, and so doesn't improve fuel consumption. The Cat is designed to remove poisonous gases and elements like Carbon monoxide and Nitrogen from the exhaust gas. Thus, its main function is to reduce excessive air pollution. It does this by reacting with the gas as it passes through the exhaust pipe. Or more specifically, it facilitates the
reaction, that’s why it is called a catalyst. One of the end products of this reaction is water which might be seen dropping off the exhaust tip at times.

Oxygen sensor

There is something else in the exhaust system which functions to measure the composition of gasses passing out the exhaust pipe. It is simply called the sensor (or a variation of that). It sends the data to the on-board computer or ECU which in turn adjusts the air-fuel ratio for optimal combustion. So the sensor(s) directly contribute to fuel economy. It is fitted after the exhaust manifold and before the Cat. Some cars do have a secondary sensor placed after the Cat which also feeds the ECU its data. But this second sensor doesn't determine the fuel economy of the car, it measure the amount of carbon emission per mile or kilometer for that cars as it is expected that the Cat would have cleaned up the gas as much as it can before it reaches the second sensor.

How Cat works
Just to add, the Cat can be removed without touching the sensor (I've not heard of an otherwise assembly). This is one of the things that happens in car upgrade workshops were stock cars are upgraded for higher performance. The cat is entirely removed, at the expense of environmental pollution because it is a major obstruction in the exhaust system and any obstruction in the exhaust system reduces engine performance. So if the cat has anything to do with fuel consumption at all, I will say it increases fuel consumption by a small bit as the car has to do more work to push out its own gas… You know how much work you have to do when you are sitting on a comfy couch and you have to push out your own exhaust gas compared to when you are standing freely and you just let it out?

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Comments

  1. My cat was removed from my car without my knowledge, that said I have been searching the web to get a definitive answer as to whether or not driving my car as it is will damage my car. I fully understand the implications in regard to the environment . I simply can't afford to have it replaced at this time. Please advise...
    Cordially,

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    Replies
    1. It depends on whether the cat was removes together with the sensors (more likely if they are arranged closely into one unit). In which case there will be a gradual build up of carbon in your engine leading to other bad effects. But if you drive a model which has the sensor and cat in different units, then removing the cat wouldn't have a bad effect on your car.
      Note: it is illegal in some countries to drive a car with the cat removed.

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  2. ''So if the cat has anything to do with fuel consumption at all, I will say it increases fuel consumption by a small bit as the car has to do more work to push out its own gas…''

    Completely missed the point that the catalytic converter is used to burn off harmful gasses which will otherwise be released to the atmosphere if it was removed. In a way yes the Cat does affect the fuel consumption because as i said earlier it burns off harmful gasses. The pre-Cat lambda sensor measures the emissions,(NOx, CO and hydrocarbons) before it enters the Cat and then the Post-Cat lambda sensor again measures the emission levels after they leave the Cat. If the post-Cat sensor relays information to the ECU informing it that there is to much of one of the emissions mentioned above it will alter the air/fuel ratio, either making the mixture leaner (less fuel injected) or richer (more fuel injected). In an ideal world an engine would be able to minimalize exhaust pollutants and keep fuel consumption to a minimum but at best it’s a compromise of the stoichiometric ratio of 14.7:1. As the mixture becomes richer to around 13.5:1 or 12.5:1 less oxides of nitrogen are produced, however carbon monoxide increases over the same loading. When the mixture becomes leaner to around 15.5:1 or 16.5:1 hydrocarbons and carbon monoxide decrease but the NOx increases. So clearly we can see that the amount of emissions produced is completely dependant on the air/fuel ratio under different loading conditions. The lambda sensor detects the amount of emissions being produced and will signal the ECU to alter the air/fuel ratio if emission levels are too high. But again it’s a compromise if the mixture is made richer carbon monoxide will increase with speed and when made leaner NOx will increase to a point before decreasing and hydrocarbons will also keep increasing.

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    Replies
    1. Great talk, and very technical too. But still doesn't dispute the fact that the cat doesn't increase improve engine fuel efficiency. The pre lambda sensor does but it technicaly, it shouldn't be considered a part of the cat

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    2. On older cars previous to EOBDII this may have been the case yes i can understand why the CAT would some what burden the engine because you get the build up of pressure in the exhaust manifold and thus the engine has to work a little bit harder to push the exhaust gasses out which means slightly higher fuel consumption. All modern day vehicles operate on EOBDII and have multi-point fuel injection so that fuel efficiency is better and cleaner.When you first start your vehicle, assuming that it is EOBD2, your ECU operates on whats called an open loop circuit. So when your engine is cold and you start it up it requires a richer air/fuel ratio so that it can reach its operating temperature quicker.Lambda sensor information is ignored until the ECU switches to Closed circuit. Once your engine has reached its operating temperature the ECU switches to a closed loop system and begins taking readings from the O2 sensors to make adjustments the the injector duration times etc... Now if the ECU operated on a closed loop circuit when the engine was cold started. The Post CAT lambda sensor would pick up on the richer air/fuel ratio and would relay this information to the ECU. The ECU would try and componsate for this by using less fuel so that the emission levels came down. but because the engine is cold it would begin to run rough until it reached its operating temperature. So lets say your engine has warmed up and the ECU is operating on closed loop. The Pre Cat lambda sensor detecs how much oxygen is present once the exhaust gasses leave the cylinders. The Post CAT lambda sensor also detects the amount of oxygen present after the exhaust gasses have passed through the CAT. So if there is a low level of oxygen this transmits to the ECU and is interpreted as a high emission reading. So both post and pre CAT sensors contribute to the fuel adjustments. Now lets get back on the main story here. Having a catalytic converter on a vehicle with EOBD1 will hinder fuel economy slightly because of the build up of pressure etc. Removing it will gain you additional power. If you remove a CAT on a modern day vehicle it will give you a slight increase in power and your car will backfire. But this extra power comes at a big cost if it is not done properly. When your remove the CAT on modern vehicles with 2 lambda sensors the ECU will be informed by the post CAT sensor that the oxygen levels are the same as the pre CAT readings and interpret this as high emissions. the ECU will componsate this by making adjustments to fuel trim. But because there is no CAT the readings will always be the same for both sensors so the ECU will constantly be trying to componsate for this and your short term and long term fuel trim will be all over the place. The fuel will eventually become rich . and constantly injecting to much fuel can do damage to your engine. When there is to much fuel being injected into the cylinder it washes the oil off the bore wall,this is known as bore wash. When to much bore wash occurs, fuel can wash down into the sump of the engine. this can cause lubrication faults and if the engine is not properly lubricated it begins to overheat. If it over heats to much you will start getting detonation of the fuel, which basically means that the fuel has ignited before the ignition stroke. When pre igniting occurs it puts strain on the piston and can cause serious damage. The piston will show signs of wear and if pre ignition is bad enough for a long period of time it can bend a conrod and when that is badly worn it will have devastating effects on your engine and your wallet.

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  3. Recently my Toyota Corolla 2003 'check' light came on. I had it checked (with OBD2 tool) and was told my 'indomie' is burnt and needs replacement.
    Would have loved to replace it, but the amount I was told is close to 30k(not in my budget now).
    I hate to see the 'check' light (n not ok with merely having it deleted).
    Pls what's the implication of driving the car for the next two months.

    ReplyDelete
  4. Firstly, the 'cat' can cost that much even in the second hand market because people hunt for then for the rare elements in them. And I'm not okay with the word 'burnt'. A 2003 Corolla's 'Cat' should still be working fine unless it was tampered with (maybe before you bought the car - stolen and replaced with bad one). Or it got damaged in the course of you and then gradually went bad. Which ever is the case can be confirmed from a careful observation.
    I'll also suggest you take the car to another auto center for a second scan, just to be sure.
    Lastly, if you continue using the car for a few months, there will be no measurable cost to you as long as the pre-lambder sensor is intact and working well. but your car will be polluting the environment more than allowed.

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  5. Thanks for your quick response/suggestion.
    The warning was deleted and hasn't come on yet, will another scan detect the issue before the light comes back on?

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  6. Many thanks for this useful report. I appriciate the query you have done here. Would have loved to replace it. Whereas pre lambda sensor does but it technicaly, it shouldn't be considered a part of the cat

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  7. Good work here. Please First of all what is lambda? And how many censor dors a MB c class 180 classic 1999 has? Thanks.

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  8. Got my cat refilled and my car came back smoking / c240 4matic 2004. What may have caused this. Pls what must be done

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    Replies
    1. Well, refilling a CAt? With what. A replacement is more like it. I doubt refilling can give the required air-tight seal for the converter to work well. That's if we assume the filaments he is filling the converter with are still active

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