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  #1  
Unread 03-22-2010, 10:24 PM
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TRW Motorsport TRW Motorsport is offline
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Default Catalytic Converter delete?

I have an '03 2.2l ecotec and I am contemplating cutting out the catalytic converter and putting some straight pipe in its place.

*THIS VEHICLE WILL NOT BE USED ON THE ROADS* I am aware that a catalytic converter is required for road use. My state does not do emissions testing (thanks god!).

I also understand that there will be an extremely small increase in performance if any, but will my MPG's and a slight sound increase? Everything else will remain stock, mufflers and headers that is.

Will the cat delete cause any problems or codes to come up?

I am just wondering after this is common practice in the diesel industry.

Thank you,
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  #2  
Unread 03-22-2010, 10:55 PM
blucavvy blucavvy is offline
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i doubt ur mpg will increase. it may actually slightly decrease. sound will probly b slightly louder, but a long enough resonator and a good muffler should take care of that.

as far as throwing codes, i'm not sure if you can hook up the rear o2 sensor into straight pipe or not. but if you can't then yeah, you'll throw a code.
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  #3  
Unread 03-25-2010, 04:18 AM
heavy chevy heavy chevy is offline
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if you get rid of or hallow out the cat it is going to throw codes and your engine is going to run rough the ecu is going to be leaning out and richening the air-fuel mixture because the o2 sensor isnot going to get to the correct temp and over all causing your fuel economy to decrease
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  #4  
Unread 04-09-2010, 09:21 AM
ryanmx ryanmx is offline
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Hey guys,
A Cat- converter delete is not a very good idea.
We had a Saturn (with an eco-tech) come in with a two cylinder misfire. The guy had run it like that for a while before he decided to get it fixed. So we replaced the coil's, plugs, solved the misfire, and sent him on his way.

He can back not even a day later with his check engine light on. He had almost four codes. Obviously because of the mis-fire, it fried that catalytic convertor. He had a cat inefficiency code (which you will get if you cut it out). He also saw an almost 10 Mpg loss.

It was explained to me like this. The ECU see's that the cat is not working properly through the information it is getting from the O2 sensors (Before and after the Cat). It is only a computer, so it has no idea the cat is pooched. What it does is throws more fuel through the engine to attempt to heat the catalytic up more, to make it more efficient. This in-turn gives you very bad mileage. This could be multiplied if there is actually no cat.

Something else to discourage you. If you decide to cut it out, A brand new catalytic converter from GM for an Eco-tech is almost $1400 Canadian. That is including the down-pipe.

Hope this helps,
Ryanmx
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  #5  
Unread 04-09-2010, 09:31 AM
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Where in the world do you guys get this information?
None of it is true.

Removing the cat won't do squat to the first pre cat O2 sensor. It changes nothing on the front o2 sensor and the secondary o2 sensor does nothing but tell the ECU that the cat is doing it's job and that's it. The secondary O2 sensor after the cat does nothing for air fuel ratios and only the front does.

You could remove the secondary O2 sensor and all you'll get is a check engine light, nothing more.

Gutting the cat will also cause more turbulence in the exhaust stream causing loss of power so your best bet is to go with a cat delete pipe of some sort or replace the cat with a resonator.

And saying the O2 sensor isn't getting the same temp only applies to the addition of a header in which the O2 sensor is placed farther back from the engine causing it to give issues with slow reading.
This can be changed to a 4 wire, preheated O2 sensor when adding a header so that the heated O2 can do the proper reading of the exhaust to give you good air fuels.

Any other advice to be answered needs to be done with correct information.
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  #6  
Unread 04-09-2010, 11:28 AM
ryanmx ryanmx is offline
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All-right.
The signal from an oxygen sensor is based on the amount of oxygen in the exhaust gas. When the sensors signal indicates a lean mixture, the computer enriches the air/fuel mixture to the engine. When the sensor reading is rich, the computer leans the air/fuel mixture.

A lean mixture produces a high level of oxygen in the exhaust and a rich mixture produces very little. The catalytic converter store the excess oxygen in it for when the mixture becomes rich. Oxygen is critical in the catalyzing of the exhaust gases, (From CO, HC, and O to H2O and CO2)

If The converter is operating properly, The signal from the pre-catalyst (HO2s1) sensor will have oscillations. The post catalyst (HO2s2) signal should be relatively flat. Once the rear signal wave reaches close to that of the first O2 sensor, the MIL is set.

In a fuel injection system, Typical inputs to the computer are:
-Manifold Pressure
-throttle position
-incoming air temperature
-engine speed, position
-engine temperature
-Oxygen in the exhaust.

OBD-II 's Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) monitor the oxygen sensor signals. This information is gathered by the PCM and used to make adjustments to the fuel control calculations. When the system is in open loop, the injectors operate at a fixed base pulse width. During a closed loop operation, the injector pulse width is either lengthened or shortened. As the voltage from the oxygen sensor increases in response to a rich mixture, the short-term fuel trim decreases, which means the base pulse width is shortened.

Once the engine reaches a specified temperature, the PCM begins to update LTFT. The adaptive setting is based on engine speed and STFT. If the STFT moves 3% and stay there for a period of time, the LTFT is adjusted. The LTFT becomes a new temporary base. So, the LTFT changes the length of the pulse width that is being changed STFT. STFT works to bring LTFT correction too 0%.

The catalytic converter is a very important part of the emissions system. So, long to short, If you remove the catalytic converter, you set the MIL, the computer goes to default (Injectors are set to the fixed base pulse width). The engine now gets fuel as if it is cold. There fore, bad fuel mileage.

Correct me if i am wrong.....?
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  #7  
Unread 04-09-2010, 01:04 PM
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If you remove the catalytic converter and space out the second O2 sensor away from the exhaust stream, the MIL light never goes off and nothing ever changes with how the car runs.
It's been done by too many people to say it's not so.
The cat is not needed but for an emissions stand point of view.

The above take is describing the first O2 sensor or bank 1 sensor which is used as described.
It states nothing of the use of the bank 2 sensor which does measure the amount of O2 in the exhaust telling the ECU that the catalyst isn't doing it's job.

For our cars, the MIL light will have no bearing on how the car runs.
I'm not sure if you're familiar with HPTuners but it's software for tuning our cars which would include controlling DTC's.
With HPTuners, you can remove the MIL from the list of DTC's and run only the front O2 with no issues.

That's no different than someone using oil fouling spark plug adapters to space out the bank 2 O2 sensor so that it's removed from the now oxygen rich exhaust from the removal of the cat. It works both ways with no issues of driveability.

Maybe this helps the conversation just a bit.
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Unread 04-09-2010, 10:44 PM
ryanmx ryanmx is offline
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That helps me alot.

I'm not too familiar with tuning of ECM's. How then does moving the rear O2 sensor make the computer think the Catalytic conveter is still there? Or is it because of the Tune that the ECM is fooled into thinking it still has one? Sorry for the lots of questions, this kind of thing intriques me.

So, What would be the overall reason for removing the catalytic converter be then? Is there any other reason except for improoved exhaust flow, possibly better exhaust scavenging, for removing the Catalytic converter? I'm sorry for being stuborn, but if Gm put it there, it's got to be there for a reason.
I'm not looking to hi-jack a thread, just searching for answers.

Ryanmx
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  #9  
Unread 04-09-2010, 11:10 PM
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It's for emissions only and to clean up the exhaust gas from hydrocarbons, nitrous oxides, and other contaminants that pollute our air.

Most states would consider the cat delete against the law so in most situations people will buy a high flow cat in place of the stocker which has a pretty good amount of back pressure designed into it.
Most high flow cats if designed right will be able to give you everything that an open pipe will give you so they're out there and you'll still be legal.

Doing the cat delete is just that, eliminating the exhaust backpressure caused by going through the catalyst material.
Also the shape of the catalytic converter causes a slow down of exhaust flow because most actually increase the diameter of the exhaust piping with the cat and then closes it down to the size of the exhaust piping which causes some turbulence over a pipe that is the same diameter of the actual exhaust.

Moving the rear O2 sensor from the exhaust stream of a cat deleted car takes it away from the oxygen enriched exhaust stream, emulating a flow of a stock cat so that the sensor doesn't get all of the flow causing a MIL light.
This works well for most and if you've got HPTuners, you can completely delete the MIL light or it ever coming on by tuning it out with no deleterious effect on the engine maintaining a good air fuel ratio.
I've done this with my car and eliminated the MIL light for the second bank O2 sensor and also did an EGR delete in which I've also eliminated the MIL light for that too.

And last, removing the cat and going with a straight pipe in it's place gives you much better flowing exhaust which would benefit you with more power and top end.
You'll lose some of the low end response of the car because in some situations, the scavenging effect is affected.
Depending on the cam profile and it's overlap of the intake and exhaust profiles, this can cause some loss of power if you don't go in and tune the car for more flow.

Also for turbo cars, the lack of a cat will give a turbo car more flow causing the turbo to spool faster since there's no restriction in the exhaust flow that would hinder free flow from the exhaust gasses.

Hope that helps and thanks for asking.
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