Back pressure

[samwichse]

Please don't just gut your cat, it will let a lot more NOx emissions out your tailpipe.

Take your converter off, soak it in a mild citric acid solution for 6-8 hours, then flush it with water at moderate pressure (not from a pressure washer, basically), remount, and if it was plugged with soot, it's good as new.

Sam

[RobertISaar]

pressure = restriction to flow. exhaust backpressure is no different.

restrictions in the exhaust = the piston has more force pushing against it while coming up during the exhaust cycle.

"needing backpressure" is an old wive's tale that still has yet to leave. commonly associated with "no backpressure will cause burned exhaust valves", among others.

[BackroadBomber]

If you gut the cat make sure you get the "spark plug non foulers" or whatever they're called... Basically they're 3 inch long tubes that are threaded and they move your o2 sensor farther from the pipe. And since an o2 sensor works on heat, it will trick your car into thinking that the cat is still working. That way your cel stays off and you can still pass inspection.

[Ryland]

You are never going to see 0 pressure in the exhaust, pretty much the lowest you can get it is 3psi, back pressure is a lousy wording because it does not describe what is really happening, it's pulses, just like a musical note from a trumpet is sound pulses, toss some weird sized chunk of pipe in there and it makes it go out of tune.
An exhaust pipe is part of the engine, if it was just a duct for exhaust then it wouldn't matter, but if you pull the exhaust manifold off the head of an engine it will hardly run, but at that point it will have -0- back pressure, exhaust is a gas, gases fallow rules of fluid dynamics, it has weight and momentum and it moves in pulses.

Fix the rest of your broken system before replacing or destroying an expensive part like a catalytic converter, the cat might not even be broken or clogged if this is a new problem.

[kanoshee]

Originally Posted by Tesla

Ignoring what the codes tell you for a minute, does the vehicle run poorly and is your fuel economy bad or gotten worse recently?

Your cat may be bad and gutting it may be fine, but it may not be your problem, be careful of jumping at shadows, look deeper to diagnose the real problem, it may actually just be a sensor problem.

Have you gone to vehicle specific discussion groups to see if yours is a common problem and how others have resolved it, everyone here has different vehicles so the info is more general and not vehicle specific.

i've already replaced my o2 sensor it was also bad and the car is weak but my effeciency is ok

[kanoshee]

Originally Posted by samwichse

Please don't just gut your cat, it will let a lot more NOx emissions out your tailpipe.

Take your converter off, soak it in a mild citric acid solution for 6-8 hours, then flush it with water at moderate pressure (not from a pressure washer, basically), remount, and if it was plugged with soot, it's good as new.

Sam

um... who gives a **** about that?

[kanoshee]

Originally Posted by BackroadBomber

If you gut the cat make sure you get the "spark plug non foulers" or whatever they're called... Basically they're 3 inch long tubes that are threaded and they move your o2 sensor farther from the pipe. And since an o2 sensor works on heat, it will trick your car into thinking that the cat is still working. That way your cel stays off and you can still pass inspection.

non emmisions county

[kanoshee]

Originally Posted by Ryland

You are never going to see 0 pressure in the exhaust, pretty much the lowest you can get it is 3psi, back pressure is a lousy wording because it does not describe what is really happening, it's pulses, just like a musical note from a trumpet is sound pulses, toss some weird sized chunk of pipe in there and it makes it go out of tune.
An exhaust pipe is part of the engine, if it was just a duct for exhaust then it wouldn't matter, but if you pull the exhaust manifold off the head of an engine it will hardly run, but at that point it will have -0- back pressure, exhaust is a gas, gases fallow rules of fluid dynamics, it has weight and momentum and it moves in pulses.

Fix the rest of your broken system before replacing or destroying an expensive part like a catalytic converter, the cat might not even be broken or clogged if this is a new problem.

nothing else on my system is broken?

[oil pan 4]

Originally Posted by BackroadBomber

If you gut the cat make sure you get the "spark plug non foulers" or whatever they're called... Basically they're 3 inch long tubes that are threaded and they move your o2 sensor farther from the pipe. And since an o2 sensor works on heat, it will trick your car into thinking that the cat is still working. That way your cel stays off and you can still pass inspection.

Taking the oxygen sensor out of the exhaust stream does make it read leaner.

[Ryland]

Originally Posted by kanoshee

nothing else on my system is broken?

my exhaust has been welded on and patch so many times it changes from stock pipe to slightly bigger pipe 4 times it has one convertor one resonator and one muffler

Cobbled together exhaust systems put more stress on the o2 sensors and more stress on the catalytic converter because it messes with the exhaust flow, there are plenty of cars out there with 300,000 miles on them that have the original catalytic converter.
If your check engine light is on with a cat code, removing it isn't going to change anything unless you replace it with a working part, replacing it with a working part is only going to last if it's not under abnormal stress.