Exhaust Backfire/Misfire at WOT - P0420 & P0430 DTCs???

[af_maineiac]

So my issue started a few months after I had my Corsa exhaust installed. I get a popping/backfiring sound at the upper RPM band (6-6.5K RPMs) while at WOT. Power/acceleration also cuts out when this happens. No other WOT issues/misfires at lower RPMs, and it never threw any DTCs.

I contacted Livernois since I'm running their v10 93 octane 3-bar tune, and they suggested I return to stock tune and see if I can replicate the issue. So after going back to stock and swapping to the 2-bar MAP sensor, I didn't get the popping/backfiring sound nearly as much....but it still did occur. And at one point, I actually threw a check engine light with corresponding P0420 & P0430 DTCs.

I'm starting to think the issue is with a misfire at WOT, probably resulting from a bad coil and/or plugs. However, since I never had the issue prior to having the Corsa exhaust, it could also be a bad O2 sensor or catalytic converter. At this point, I'm not really sure how to further diagnose, so I may end up taking it to the dealer to find the root cause.

Has anyone else experienced something similar? And if so, any suggestions? TIA

 

[6500rpm]

Did you change the down pipes? Pretty odd to have Cat efficiency dtc's on both banks at the same time with OEM equipment. If they were both crapping out and possibly restricting I'd think you may be able to see something on the MAP values. Odd for a misfire, no P03xx dtc's?

 

[mrhighcaliber]

Have u changed your plugs in the last 25-30k miles? If not I would suggest checking and changing them. .030 is the lms recommended gap. Stock is .038ish (they aren't consistent from plug to plug).

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[SHOdded]

Doublecheck the exhaust system install. Could simply be a loose fastener or a small leak that becomes obvious at high RPM (gaskets). Also monitor fuel trims, there might be too much fuel in the exhaust at high rpm's.

 

[af_maineiac]

Did you change the down pipes? Pretty odd to have Cat efficiency dtc's on both banks at the same time with OEM equipment. If they were both crapping out and possibly restricting I'd think you may be able to see something on the MAP values. Odd for a misfire, no P03xx dtc's?

Yep....beginning to think it's more exhaust-related than a misfire. And yes, I do have the down pipes from Livernois as well. Will look into it further next week. Thanks!

 

[af_maineiac]

Doublecheck the exhaust system install. Could simply be a loose fastener or a small leak that becomes obvious at high RPM (gaskets). Also monitor fuel trims, there might be too much fuel in the exhaust at high rpm's.

I think you're on the right track. I'm wondering if the popping noise is a result of a plugged-up exhaust and excessive back pressure feeding back into the motor....perhaps something even rattling around and intermittently plugging the pipe. I picked up some Cataclean and will give that a try.