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2011 GT CEL p0420/p0430

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Old 7/9/18, 12:11 AM
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2011 GT CEL p0420/p0430

Recently, I bought a 2011 GT, 6 sp (mt82) with 58k. It has some basic bolt ons, but nothing special. Factory CAI, BBK long tube headers, GT500 axle back. As of right now, I'm not sure if the cats, h pipe or resonators have been changed. Though I am going to get under it tomorrow to see. I don't think any custom tunes were done either. CEL has been on, and it's showing p0420/p0430. I can clear them out, and usually they will pop back up after 10-15 miles. Haven't had any other issues so far outside of exhaust fumes that are a bit more noticeable than normal, when standing next to it, while its running.

I've spent a few hours on different forums, but have yet to come up with anything solid. Some say it's harmless, some say it isn't. I've heard that it's the rear of sensors, or even a leak on the intake. So I'm just curious if anyone has a better idea or first hand experience with this issue. Could the headers be the cause? Mainly, I just want to be sure that this isn't going to cause harm to the engine.
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Old 7/9/18, 05:29 AM
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'If' you have long tube headers, your catts and h pipe have been messed with.
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Old 7/9/18, 05:41 AM
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That's what I was thinking. So I need to get under it and see exactly what has been done, to try to start narrowing down what the issue could be.
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Old 7/9/18, 06:39 AM
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Well, I took a quick look underneath (kind of a pain, seeing that it's been lowered a bit) and from what I can see, the BBK's are dumping into 3" pipes, with an H pipe, no cats, with resonators just before the axle, ending with the GT500 mufflers. I'm going to put it on jacks later today, to confirm and take pics. So at least I now know why it has the noticeable fumes.
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Old 7/9/18, 03:56 PM
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Mustang P0430 Catalyst System Efficiency Below Threshold
Mustang P0420 Catalyst System Efficiency Below Threshold
These are the codes that are coming up. Since you have no cats I'm going to assume that the O2 sensors are AFTER the cats and that is what's giving you the CEL. You might be able to take care of it with a tune but don't expect to pass any type of emissions inspection without anything hinky taking place due to the fact you have DTC codes coming up and when they look under the vehicle they won't see any cats. It shouldn't hurt your engine but it certainly ain't going away on it's own.
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Old 7/9/18, 05:37 PM
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Luckily, my state has no inspection or emissions check of any kind. I'm planning on swapping out the GT500 mufflers, with some good aftermarket ones. I'm also planning on upgrading the factory CAI, and possibly a Boss 302 intake, so I am going to need a tune anyway. So I figure that whenever I order a tuner, I'll have the rear o2 sensors turned off.
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Old 7/9/18, 07:03 PM
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Originally Posted by valkyrie4401 View Post
Luckily, my state has no inspection or emissions check of any kind.
WOW, what mystical wonderland do you live in! At least here in NJ they only test for emissions. They stopped doing the "safety" tests awhile ago.
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Old 7/9/18, 07:12 PM
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No testing at all in Oklahoma City. Hell, we even have a lot of gas stations with ethanol-free gasoline.
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Old 7/10/18, 11:44 AM
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Just so you're aware, once the cats are removed, the rear 02 sensors require being turned off, otherwise, this is what's causing those catalysts efficiency codes to keep popping up along with getting a CEL. Also, long tube headers require a custom tune and will not run properly on the stock calibration.

I also recommend that when you order a tuner, make sure that you order a custom tuning programmer from a custom tuning dealer, such as Lund, JDM engineering or a local custom tuning dealer in your area. However whatever you do, do not order a preloaded tuner from vendors such as VMP, Steeda and especially from AM/Bama as VMP will NOT turn off the rear 02 sensors in any of their calibration tunes and Steeda, AM/Bama do not include custom tuning files for long tube headers in any of their programmers.

That being said, whoever you purchased your car from, should've also included their custom tuning device if they had no intentions of putting the vehicle back to stock prior to selling it
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Old 7/10/18, 08:13 PM
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I've actually have got a shop within a few miles of where I live, that builds street/race cars, tunes, ect. I'm just going to take it there, and have them dyno tune it. I was considering ordering a custom tuner and tune from Lund, or a similar place. But now that I know that I have a shop close to me, with a great reputation, I'll just take it there.
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Old 7/11/18, 11:03 PM
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Originally Posted by valkyrie4401 View Post
I've actually have got a shop within a few miles of where I live, that builds street/race cars, tunes, ect. I'm just going to take it there, and have them dyno tune it. I was considering ordering a custom tuner and tune from Lund, or a similar place. But now that I know that I have a shop close to me, with a great reputation, I'll just take it there.
You made a very wise choice IMO, as you certainly can't go wrong with getting your car custom tuned on the dyno
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Old 7/13/18, 07:05 PM
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Originally Posted by valkyrie4401 View Post
Recently, I bought a 2011 GT, 6 sp (mt82) with 58k. It has some basic bolt ons, but nothing special. Factory CAI, BBK long tube headers, GT500 axle back. As of right now, I'm not sure if the cats, h pipe or resonators have been changed. Though I am going to get under it tomorrow to see. I don't think any custom tunes were done either. CEL has been on, and it's showing p0420/p0430. I can clear them out, and usually they will pop back up after 10-15 miles. Haven't had any other issues so far outside of exhaust fumes that are a bit more noticeable than normal, when standing next to it, while its running.

I've spent a few hours on different forums, but have yet to come up with anything solid. Some say it's harmless, some say it isn't. I've heard that it's the rear of sensors, or even a leak on the intake. So I'm just curious if anyone has a better idea or first hand experience with this issue. Could the headers be the cause? Mainly, I just want to be sure that this isn't going to cause harm to the engine.
I used 02 extensions to get rid of this code on mine. If you try to "turn off" rear 02s they just have the CEL ignore the code.
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