Thread: N54 Backfiring?
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      07-12-2011, 09:01 PM   #20
The Fat Stig
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Drives: 2010 135i
Join Date: Dec 2010
Location: 2003 Stg 3+ SRT-4

iTrader: (1)

Originally Posted by evilstib View Post
Replaced stock midpipes with (previously owned) CP-e catless midpipes. The Downpipes & muffler are stock.

I love the tone, but I get a lot of backfiring now. I didn't think removing 2 of 4 cats and the resonator would cause this.

Anyone else see this before?
It's probably burbling/crackling or "popcorn" as I've heard it referred to before. I doubt that BMW programs it into the tune, but some other vehicles have tunes that specifically inject fuel on overrun/vacuum to give the crackle on decel. If you think this thing crackles, you should hear my stage 3 SRT4 with a 3" Side exit exhaust. I can set off car alarms with the crackle, so I tuned most of it out. I think that some of the crackle exists only because you're always going to have a small amount of overlap on the cam, and that's what you're hearing.

If it's a true lean backfire, and it's only on decel, then no big deal (BMW probably just got agressive and turned off the fuel injectors completely on decel), but if it's a lean backfire at WOT, then that would be bad.