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I have a 2005 2.4L automatic 3g that I bought used. The check engine light has been on since my purchase and the current code is popping up (refer to image). The car has a CAT delete for a straight pipe which was done before I bought the car. The car has constantly been going in and out of limp mode with no change to the check engine light. Recently spoke to another 3g owner and he suggested to get a better o2 sensor for the CAT delete. If this is the best option, how would I go through replacing the sensor and what part would be best to clear the codes and work with the CAT delete. Also open to more suggestions other than a o2 sensor replacement other than to get another CAT.
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2001 Spyder GT. Koni adjustable shocks. ST sway bar.17X8.5 rims. LED headlights.
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As an old retire mechanic, I am constantly amazed at the number of people who take out "cats", remove sensors, and generally "jack up" thier computer EFI systems and expect them to work well. I would strongly recommend you reinstall the cat and put an O2 sensor back in it. The computer does not know what the engine is doing without the imput from the O2. That being said...Hey, it is your car. ...J.D.
 

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I agree with @WhiteSpyder aka J.D... This may be an expensive project but the result is what you are after. The power gained from a cat delete is not worth the hassle. Personally, I think it's all noise.
 

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2001 Spyder GT. Koni adjustable shocks. ST sway bar.17X8.5 rims. LED headlights.
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I have been working on engines since JFK entered the White House. First as a hobby. Then as a profession. Then as as a hobby again after going to college. Lastly as a retire old guy that still loves machinery. There are better ways to get that 5% horsepower gain you THIINK you are getting by removing a cat. But removing the O2 sensor is like cutting off your fingers so your hand will work better. Without the O2 sensor, the computer goes into what is referred to "limp" mode. The computer can no longer adjust mixture as needed. It cannot see changes in exhaust mixture. It has to rely solely on the MAF that is measuring the volume of air coming into the throttle body. This causes it to have an incomplete calculation to work with. The engineers have given the system the limp mode so you can at least get home. And that is the SIMPLE explanation. ...J.D.
 

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I have a 2005 2.4L automatic 3g that I bought used. The check engine light has been on since my purchase and the current code is popping up (refer to image). The car has a CAT delete for a straight pipe which was done before I bought the car. The car has constantly been going in and out of limp mode with no change to the check engine light. Recently spoke to another 3g owner and he suggested to get a better o2 sensor for the CAT delete. If this is the best option, how would I go through replacing the sensor and what part would be best to clear the codes and work with the CAT delete. Also open to more suggestions other than a o2 sensor replacement other than to get another CAT.
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First try replacing the O2 sensor (Bank 1, Sensor 1) which is located on the exhaust manifold under the top shield. If you still had a CAT, the second O2 sensor (Bank 1, Sensor 2) would be located on the pipe right near the CAT. When a CAT delete is done, people will drill a bung hole in the "straight pipe" and use a "spark plug spacer" with the second O2 sensor to avoid a CEL. The connector for the second O2 sensor is under the shifter console inside the car. You should check if there is a second O2 sensor, assuming the previous owner kept it installed after the CAT delete. I believe that only the first sensor sends info back to the ECU to adjust AIR/FUEL trim, and the second just provides emissions info but will still trigger a code. So in other words, both sensors provide emissions info and will trigger codes, but only the first will actually affect how the engine runs.
 

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2001 Spyder GT. Koni adjustable shocks. ST sway bar.17X8.5 rims. LED headlights.
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The downstream O2 provides long term fuel trims. The O2 in the exhaust manifold sets the initial mixture. Both play a part in the mixture calculations. One thing to note about Mitsubishi systems is that you need to take care in choosing a new O2 sensor. Mitsubishi systems do not quite work like most other manufactures. Make sure the O2 you buy is specifically for Mitsubishi. The generic ones will cause you problems. I usually use Bosch, but just make sure it has the correct specifications. ...J.D.
 

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The downstream O2 provides long term fuel trims. The O2 in the exhaust manifold sets the initial mixture. Both play a part in the mixture calculations. One thing to note about Mitsubishi systems is that you need to take care in choosing a new O2 sensor. Mitsubishi systems do not quite work like most other manufactures. Make sure the O2 you buy is specifically for Mitsubishi. The generic ones will cause you problems. I usually use Bosch, but just make sure it has the correct specifications. ...J.D.
With your experience, I wont argue about the role of the downstream O2 sensor. My response was based on what other members have said AND my own experience of when my downstream sensor went bad and had no affect on how my engine ran. It just simply threw a code, so I replaced it (Bosch). I personally have never considered doing a CAT delete, but others have successfully done it while "fooling" the ECU with a spark plug spacer, and apparently no adverse affect on engine performance. Again, not arguing, just repeating what I've heard from others who seemed to know what they were talking about. Generally, however, I would never "recommend" altering the original engineering design. I do, however, sometimes mention what others have done and their results.
 

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My "experience" in these things is still in the learning stages as well. At 76 years old, there is still much to learn. I left the automotive trade in the mid-1980's, so from then on I have just been a hobbyist and worked as an engineer in another trade. As I "understand it"...The primary O2 is used in the initial calculation along with MAF, Absolute Manifold Pressure and a few other things, to determine injector dwell time. The secondary O2 downstream is used as feedback to fine tune the system. If the mixture is still a little off coming down the pipe, the computer sees a rich/lean signal from the secondary O2 and makes adjustments in it's calculations. The system has the ability to "learn" as it makes these corrections. The end product is it "knows itself" somewhat when the fuel trims reset. As for the O2 sensor, I THINK I know why Mitsubishi's O2 works differently, but I will not go there because I cannot verify what I suspect. I would not want to mislead anyone. ...J.D.
 
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