Bogging when clearing P0420 code?
 

Hello all,

Did some research on my issue and while I found a lot of threads with the P0420 code, I couldn't find many mentioning the bogging issue I have, so hopefully this isn't a repeat of another thread out there, and if it is, sorry! But anyways, here it is:


TL;DR:

2015 BRZ 6-speed

P0420: Catalyst System Efficiency Below Threshold (Bank 1)

Mods:
Perrin cold air intake
MXP UEL headers
MXP overpipe
Stock midpipe
Muffler delete

My car bogs down when accelerating every time I clear a P0420 CEL for a few days after recently getting a muffler delete, even though all my other mods are about 2 years old and have never given me issues (specifically the headers). Is this normal? Has anyone else experienced this?




Full story:

I have a 6-speed '15 BRZ and for quite some time now, I have been running a Perrin cold air intake, MXP catless UEL headers, MXP overpipe, stock midpipe, and stock exhaust. I have had it that way for almost 2 years without a single issue or check engine light and have loved the feel of it. However, I felt I wanted it a bit louder, so I recently opted for a muffler delete about a month ago since it was a cheaper option and I actually liked the sound from what I heard on YouTube over some other cheaper exhausts and I really wanted to get the rumbles. People would complain about the drone (and now I know why!), but I don't recall anyone saying that deleting the muffler would throw any codes, so I went through with it.

When I first got the muffler delete done, I didn't notice any "gains", but I also did not notice any losses in power, so all was loud and good. About 2 weeks ago, my CEL came on while driving. I have a pocket OBDII scanner that I carry around with me, so I pulled over, checked the code, and it was a P0420... which I expected considering my full setup, but I was surprised that it took so long to show up considering I expected the header install 2 years ago would be the one to throw the code, not the muffler delete. But since I knew what it wasn't anything life-threatening, I erased the CEL and went back about my business.

The next time I turned my car on, I noticed it wanted to almost stall on me when warming up, although it never did on its own during the warm up process. I went to drive and I noticed I needed to give it more gas to get moving and the clutch was REALLY sensitive, almost like it wasn't getting much gas at all. Overall, the feeling of the car was very sluggish and felt like it wanted to stall when coming to a stop. At two points that same day, I stalled the car while approaching a stop sign... not when taking off from it, but while I was coasting to a stop, which I thought was super weird. The same thing happened at a red light, which was embarrassing, but I knew it wasn't my fault (although no one around me did) since my car was acting different.

I drove like this for a few days and started to notice the car reverting back to normal the more I drove. Finally, after another 2 weeks or so, the car felt 100% as before the first CEL and I was happy... but then........ P0420 once again :/ So just as last time, I pulled over checked the code, saw that was the only code, and then cleared it. I drove home normally, turned off the car. I went to drive the car again the day after, lo and behold, the bogging issue came back. So now I am waiting for the car to "correct" itself in the coming week or so with normal driving and expecting the light to come back on soon.

I am assuming I will need a tune in order to properly solve this issue. An OFT was in my plans for the future, but now that I have this issue going, if the OFT will help, I may have to get it sooner than later unless there are other equally-effective cheaper alternatives.

But now my question is would clearing the code reset the ECU and would it have to re-learn to adjust the AFR and all that? I thought clearing the code would just remove the code but maintain all the parameters without resetting the ECU.

Is it normal for the car to bog after clearing a code, specifically the P0420 CEL? Has this happened to anyone else? And is the OFT tune the best [reasonably-priced] option to fix the CEL and prevent the bogging issue?

If I get the OFT, I do plan on running E85 since I have a station right down the street from me. The E85 tune should also have it's own parameters to help not throw a CEL, right?

Any help is much appreciated. Thank you!

cat efficiency CEL shouldn't affect performance. IIRC it should only disable cruise control. Are you sure that it's the only CEL thrown?
As you run catless headers, but mention "OFT" "in my plans for the future", i guess you are running stock tune? You really should install proper ecu tune for those headers, as it will 1) increase gains from very same bolt-on mods, 2) most tuners, be it via ecutek or in OFT tunes, in tunes made for catless headers disable those cat efficiency checks for this specific CEL to not get thrown.

Thank you for replying. I agree in thinking that it shouldn't affect performance, but I found it odd that it did, which is why I am wondering if it's normal or if it could be something else.

Technically I got 3 codes on the OBDII scan tool, but all the same P0420:

P0420 PND
P0420 CFN
P0420 PRM

I did a little research and I found that meant PND - pending, CFN - confirmed, and PRM - permanent. Info was gathered from here. So, with that said, I think I could assume all 3 codes are essentially the same code.

And yes, I do currently have a stock tune. I knew I was going to need one with everything I have installed and I was expecting a CEL to throw the P0420 eventually, but I was not expecting the performance issue with the CEL, which is what is worrying me.

It's only normal for it to bog after flashing a new tune, what tool are you using to reset the code? It might be doing more than just resetting the DTCs. This is the same process that occurs with after a flash where it takes the ecu a certain period of time to learn throttle input and some of the fuel tables and other things. During that period the car is sluggish.


Also you made a good decision getting an OFT, as otherwise you're essentially throwing horsepower and mpg out the window without a tune. All the UEL based tunes have the P0420 CEL disabled as well as other fixes and useful edits baked into them, it's also super fun to play with it in romraider.

So it is normal?

I am using an OTC PocketScan Code Reader:

https://www.otctools.com/sites/defau...?itok=RfuKrFoF

In that case, from what you're saying, this should happen every time I remove the code since it is reflashing the ECU, correct?

I have also heard that the ECU will cut power to the engine while a code is present, is this true?

I have not gotten the OFT yet, but I will get it eventually, and now sooner than later if this problem persists. I wasn't planning on getting it soon since I was going to hold off on modding my car at least until I graduate school (1 year left), but we will see if I end up treating myself soon enough to some E85 tunes :thumbup: Student loans FTW! lol

Not reflashing so much as resetting.

You're not going to pass emissions when that code pops up, P0420 doesn't kill power on our cars, but not running a tune definitely is a waste of money in my opinion :lol:

That actually raises a good question, can I pass smog with the OFT tune? I'm assuming not, right? I know the UEL headers will probably have to come off for the smog check, but in any case where I get some guy on his first day at work and doesn't notice my headers are catless, would the OFT allow the system to think it passes the sniff test considering it tunes the ECU to not trigger the P0420 code?

Hopefully that makes sense...

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If you're asking that question you need to do way more research, it varies between jurisdictions.

In my area it passed easily several times because it showed emissions readiness and passed there "visual check".

It won't pass a sniffer test because it will obviously show particulates in the exhaust. You have to know what your area does emissions wise, otherwise you shouldn't have bought a header in the first place or should just put your stock header back on....

I understood the consequences that came with the UEL upon getting them, I'm just wondering if there was a chance the future emissions test would be any easier by somehow tricking the system with the OFT, but if not, I am already prepared to swap out the UEL headers for my stock ones as I kept mine and are stored away for that specific reason. The way I see it, I bought my car brand new and I don't have to smog the car for 5 years, so I figured I have some time before California law slaps me in the face, so why not enjoy the rumbles in the meantime? Lol

But it is what it is, I still have about a year or so left before I have to smog it, so I'll see if I can have some E85 fun before that time comes. If worse comes to worst, I'll just swap everything to stock. I just want to make sure I don't have any lasting permanent damage in the meantime with anything regarding my car, not just the catless headers.

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Yea you won't have to worry about permanent damage. OFT isn't a guarantee you'll pass emissions but I passed in my area of the state with no issues since 2016 so take it with a grain of salt.

Oh alright, good to hear. Thanks for your help, man!

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You need to disable the P0420 DTC in the tune. Whether that passes emissions I cannot guarantee but will stop the code popping up and having to reset the ECU every time the codes are cleared. It's the reset that is causing the "loss of power". You just have to do the standard reset routine every time you clear the code (leave on accessory for 1 min, press pedal to the floor 5 times, let idle for 30 secs etc.).

I'll go ahead and do that when I get enough cash to drop on an OFT since it wasn't in my plans right now, but I'll surely do that then

I'm going to be honest with you and say I have never heard of the reset process you are talking about... Before I got the OBDII tool, I would always just disconnect the battery for a few minutes and reconnect it and drive off normally (without flooring it, of course), but now I just clear the codes through the scan tool without disconnecting the batrery or none of that. I've never known that you should let the car idle or press the gas pedal or none of that. Is that bad? :0 Can you point me in the direction where I could find more info about this procedure?

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OP typically clearing codes via a tool/scanner/etc. will reset the ecu and in turn tell it to learn fresh fuel trims among other things. A battery disconnect can do the same thing, however. I wouldn't get yourself too worked up over the learning procedure though. Let the car idle for a minute afterward and everything else should be fair game.

Good on you for finally looking into getting the car tuned, albeit a bit late lol. Oh also, if you're planning on running a base OFT rom be sure to take a few logs when you load it up to make sure you don't need any changes due to the Perrin piece. OFT canned roms are made with the stock intake in mind.