Why you should keep your cat converter

[Genie47]

There are 2 ways the catalytic converter degrades.

 

1. You operated and the catalytic converter is no more.

2. You used engine oil that is very high in ZDDP and your engine suffered a blow-by releasing this additive in large amounts into the cat.

 

Either way, the cat will die. One by murder, one by slow death.

 

When a cat degrades, the downstream oxygen sensor signals to the ECU. The ECU responds by increasing fueling and retard the ignition.

 

This means you lose power AND have poorer FC. You have been warned.

[Nismo]

poor little cat....

[Maded]

meow!

[Gadgeter]

you coming down tonight? If yes, I'll share my cat story with you.

[Hoppe]

Genie,

there's another reason lah. To pass LTA inspection.

That's why I put my cat back...hehe

[Decibel]

Was thinking of operating my exhaust, shouldnt there be an increase in power instead of loss? Don't understand what you're trying to say

[Nocturnal113]

Hm, there should be a power gain. I think what he is saying is if you do a decat without bypassing the o2 sensor. But most of the time, when you decat, they will put a o2 fooler to bypass the ECU feedback. That way, you don't get the "check engine light" coming on.

If you are doing to decat, you should also consider installing a piggyback ECU to fine tune your engine settings with the new mod. That way, you can get the most out of your modification.

[Normal_aspirated]

wat i noe, the newer ECU normally compare the second O2 sensor signal with the first one (b4 the cat). If it detect any difference, it will give "engine check light" alarm, indicating the cat is faulty.

[Kytl68]

LTA will check your emission if you remove the CAT and if you fail than problem .. but if you pass ... it's ok to be without CAT.

[Cantona156]

Even if you fail, but you have a cat, it is also ok.

My car's emission is 20 times more than the VW Beetle infront of me (CO, PPM etc)

But I still pass.

 

[Hoppe]

you mean your car is cat-less?

[Slowpoke156]

You are simply generalising.

 

For Euro2 cars, the lambda sensor is before the cat, so it makes no difference whether or not the cat is present, except during the bi-annual inspections where your emissions may register much higher values.

 

For Euro3 cars, many of them have 2 cats, 1 right after the exhaust manifold and the other after the lambda sensor. In this case, removal of the first cat may cause the lambda sensors to trigger a response from the ECU, be it the infamous "Check Engine" light to fuelling and ignition errors found in engine diagnostics. You can add a resistor to force the lambda sensor to generate a consistently high value (causing the ECU to go open loop) and then use a piggyback computer to control fuelling and ignition. This is the best practice for power and economy. Removing the second cat will be similar to that on Euro2 cars.

 

In many cars, people lose power and economy because:

1. They do open cone intakes as well which take in hot air from the engine bay

2. A fully "opened" exhaust system causes loss of resonating exhaust pulses which actually help move the exhaust gases out more effectively at lower rpms

3. Many people do enlarged down and centre pipes which create the same result as in 2

4. They simply punch through the cat and not remove it and replace with a pipe of similar diamater to the rest of the exhaust, causing flow disruption and hence loss of power