Taking the cats. off
Thread Starter
Intermediate
Joined: May 2005
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Taking the cats. off
I would like to remove the cats from my C6. I installed a Corsa Sport exauhst already, and want a louder sound, plus i think with the cats it has too much back pressure. I plan to replace the cats with a bolt on pipe. The problem is that i dont want to loose the warranty. Will i be able to put the cats back on if i have a problem and need to bring it for service and they wouldn't know? Will the check engin light shut off when i put the cats back on?
Instructor
Joined: Mar 2005
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You can use o2 simulators to not get a check engine light, I would recommend taking that route.
Also, I am unsure if you can even unbolt the cats from the headers or if they are welded on. Even if you could you would need more than just a straight pipe to match up to the exhaust. However any competent muffler shop should be able to make this pipe for you.
Also, I am unsure if you can even unbolt the cats from the headers or if they are welded on. Even if you could you would need more than just a straight pipe to match up to the exhaust. However any competent muffler shop should be able to make this pipe for you.
Le Mans Master
Joined: Aug 2000
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From: Murphy TX
O2 simulator is a device which outputs a set voltage, so instead of a sensor sending variable voltage, the sim sends a set voltage and the computer things the sensor is still there.
I do not believe the cats are bolt-in. I could be wrong.
I do not believe the cats are bolt-in. I could be wrong.
Race Director
Joined: Oct 2004
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Originally Posted by TommyV
Remember, depending on where you live, removing the cats is illegal, and in Calif, most tuners won't do it.
It is ok to do it to a race-only car, ie one that is trailered any time it is on public highways. That's how the vendors get away with selling long tube headers, "test pipes", "high flow" cats, etc. Big disclaimer in the ads saying "off road use only".
The feds do police the shops, which is why few reputable shops will risk removing or relocating the cats on a street licensed car. An individual doing it on his own is less likely to be caught, unless his state inspection catches him, or someone drops a dime on him to the feds' tip line. (Dealer might do that if there's a warranty dispute.) But the consequences if you are caught are stiff enough that they ought to make you think twice.
Last edited by shopdog; May 6, 2005 at 02:27 AM.
Pro
Joined: Nov 2003
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From: Olathe Kansas
Originally Posted by MiKe88
I would like to remove the cats from my C6. I installed a Corsa Sport exauhst already, and want a louder sound, plus i think with the cats it has too much back pressure. I plan to replace the cats with a bolt on pipe. The problem is that i dont want to loose the warranty. Will i be able to put the cats back on if i have a problem and need to bring it for service and they wouldn't know? Will the check engin light shut off when i put the cats back on?
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Racer
Joined: Nov 2004
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I don't think the simulators will work, the computer changes the fuel trim and looks for changes in the O2 readings, if they aren't there, a code sets. You could disconnect the wire for that light...which would mean you wouldn't know when it was on, but since it would be on all the time anyhow, no information is lost.
Le Mans Master
Joined: Aug 2000
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From: Murphy TX
Originally Posted by TommyV
Remember, depending on where you live, removing the cats is illegal, and in Calif, most tuners won't do it.
Tuners will do it, and they will tell you it's for 'off-road use' only as a disclaimer of their liability.
Le Mans Master
Joined: Aug 2000
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From: Murphy TX
Originally Posted by OttoNP
I don't think the simulators will work, the computer changes the fuel trim and looks for changes in the O2 readings, if they aren't there, a code sets. You could disconnect the wire for that light...which would mean you wouldn't know when it was on, but since it would be on all the time anyhow, no information is lost.
They send the computer a voltage.
If the sensor is removed the computer gets no reading and throws codes thinking the sensors are dead.
The sims send a consistent voltage and the computer things all is well.
Race Director
Joined: Jan 2005
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From: Daytona Beach FL
Originally Posted by yellow01
Uh, this is exactly why the O2 sims DO work.
They send the computer a voltage.
If the sensor is removed the computer gets no reading and throws codes thinking the sensors are dead.
The sims send a consistent voltage and the computer things all is well.
They send the computer a voltage.
If the sensor is removed the computer gets no reading and throws codes thinking the sensors are dead.
The sims send a consistent voltage and the computer things all is well.
OttoNP indicates that the O2 sensors send info to the computer about changing O2 readings (i.e., CHANGING voltage) to the computer so it can adjust the fuel trim.
The O2 simulators, as you indicate, probably send a "consistent" voltage to the computer. No codes, but also no adjustments to fuel trim for varying O2 levels.
As I said, I don't know anything about how this system works. Standing by to learn something!!!
Bob
Le Mans Master
Joined: Aug 2000
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From: Murphy TX
O2 sims send A set voltage.
If I remember correctly, the 2nd set of O2 sims are primarily there to monitor the Cat's functionality.
The majority (if not all) of closed loop operation is handled by the 1st set of sensors.
Therefore, sending a set, in spec voltage from the 2nd set make the car believe that the cats are working fine, and that all is well.
I have a copy (pdf, 4 Meg) of the Holden genIII training manual which discusses everything about the LSx engine. I can email if so desired. In this manual it does not even discuss the 2nd O2 sensors.
If I remember correctly, the 2nd set of O2 sims are primarily there to monitor the Cat's functionality.
The majority (if not all) of closed loop operation is handled by the 1st set of sensors.
Therefore, sending a set, in spec voltage from the 2nd set make the car believe that the cats are working fine, and that all is well.
I have a copy (pdf, 4 Meg) of the Holden genIII training manual which discusses everything about the LSx engine. I can email if so desired. In this manual it does not even discuss the 2nd O2 sensors.
Race Director
Joined: Jan 2005
Posts: 10,924
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From: Daytona Beach FL
Originally Posted by yellow01
O2 sims send A set voltage.
If I remember correctly, the 2nd set of O2 sims are primarily there to monitor the Cat's functionality.
The majority (if not all) of closed loop operation is handled by the 1st set of sensors.
Therefore, sending a set, in spec voltage from the 2nd set make the car believe that the cats are working fine, and that all is well.
I have a copy (pdf, 4 Meg) of the Holden genIII training manual which discusses everything about the LSx engine. I can email if so desired. In this manual it does not even discuss the 2nd O2 sensors.
If I remember correctly, the 2nd set of O2 sims are primarily there to monitor the Cat's functionality.
The majority (if not all) of closed loop operation is handled by the 1st set of sensors.
Therefore, sending a set, in spec voltage from the 2nd set make the car believe that the cats are working fine, and that all is well.
I have a copy (pdf, 4 Meg) of the Holden genIII training manual which discusses everything about the LSx engine. I can email if so desired. In this manual it does not even discuss the 2nd O2 sensors.
It sounds like the O2 simulators are sorta like a CAGS eliminator - just on the end of the wire, so that even though it's not hooked up anymore, the system still senses that it is. That way you don't get the check engine light or codes.
Thanks, Bob
Racer
Joined: Nov 2004
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To elaborate a little more...
The O2 sensors send a voltage that indicates the amount of oxygen in the exhaust. The ECM adjust the injectors duty cycle for optimal performance. The voltage of the O2 sensors fluctates based on these adjustments and the ECM checks for this, this may be a newer thing. The ECM attempts to have the voltage cross back and forth around a specific value but it will also change it every now and then to make sure the O2 sensors are reacting correctly. I would be impressed if the simulators could simulate the changes in voltage that the real ones undergo matching the timing of the injector duty cycles...
The O2 sensors send a voltage that indicates the amount of oxygen in the exhaust. The ECM adjust the injectors duty cycle for optimal performance. The voltage of the O2 sensors fluctates based on these adjustments and the ECM checks for this, this may be a newer thing. The ECM attempts to have the voltage cross back and forth around a specific value but it will also change it every now and then to make sure the O2 sensors are reacting correctly. I would be impressed if the simulators could simulate the changes in voltage that the real ones undergo matching the timing of the injector duty cycles...
Racer
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Specific Example:
DTC P0132 or P0152 will set if the O2 sensor voltage is over 1052 mv for 48 seconds during a rich test or if it more than 580mv for 5 seconds during a decel fuel cutoff test. If the O2 sensor just sent a constant voltage, you can see these codes would set...
DTC P0132 or P0152 will set if the O2 sensor voltage is over 1052 mv for 48 seconds during a rich test or if it more than 580mv for 5 seconds during a decel fuel cutoff test. If the O2 sensor just sent a constant voltage, you can see these codes would set...
Race Director
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From: Virginia Bch VA
Cruise-In VI Veteran
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St. Jude Donor '06
One Solution
Originally Posted by shopdog
... it is Federal law.... $10,000 fine ...both liable to be fined.
..."high flow" cats, etc. Big disclaimer in the ads saying "off road use only".
The feds (*****) do police the shops, ...someone drops a dime on him to the feds' tip line. (neighbor *****) ...if you are caught are stiff enough that they ought to make you think twice.
..."high flow" cats, etc. Big disclaimer in the ads saying "off road use only".
The feds (*****) do police the shops, ...someone drops a dime on him to the feds' tip line. (neighbor *****) ...if you are caught are stiff enough that they ought to make you think twice.
Race Director
Joined: Oct 2004
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Originally Posted by JFTaylor
Thanks Mr Dog. You are 100% correct. Those damn tree huggers. A thought would be to take off the orig CAT and gut it. It would be there for a visual inspection. Claim ignorance if cited.
Ignorance is no excuse under the law, gutted cats will land you a fine just as surely as removing them altogether. It isn't at all clear that a gutted cat will flow better than an unmodified one either. Modern cats are designed with pretty low restriction. Who's to say that a gutted cat won't behave like an old glasspack, straight through but with a higher flow restriction than a properly designed chambered muffler.
Race Director
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From: Virginia Bch VA
Cruise-In VI Veteran
Cruise-In VII Veteran
St. Jude Donor '06
Originally Posted by shopdog
I don't have anything against clean air. But the anti-tampering regulations are primarily a regulatory convenience, eliminating the need for tailpipe sniffer tests for 1996 and newer cars. I say that as long as a car can pass the tailpipe sniffer test, the feds shouldn't care what has been done to the car. But they do, and that's the world we have to live in, so tampering with emissions equipment is a high risk action.
Ignorance is no excuse under the law, gutted cats will land you a fine just as surely as removing them altogether. It isn't at all clear that a gutted cat will flow better than an unmodified one either. Modern cats are designed with pretty low restriction. Who's to say that a gutted cat won't behave like an old glasspack, straight through but with a higher flow restriction than a properly designed chambered muffler.
Ignorance is no excuse under the law, gutted cats will land you a fine just as surely as removing them altogether. It isn't at all clear that a gutted cat will flow better than an unmodified one either. Modern cats are designed with pretty low restriction. Who's to say that a gutted cat won't behave like an old glasspack, straight through but with a higher flow restriction than a properly designed chambered muffler.
