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      07-09-2011, 10:50 AM   #1
evilstib
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N54 Backfiring?

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?
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      07-09-2011, 02:41 PM   #2
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Quote:
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?
are you sure its backfiring and not just the "gurgling and popping"? I have full catless and I get lots of gurgling and popping but they only time i ever get a hint of backfire is when i am wot at low rpm and then shift gears before 3500 or so
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      07-11-2011, 08:29 AM   #3
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[quote=330iSB;9988993][quote=evilstib;9987893]Replaced stock midpipes with (previously owned) CP-e catless midpipes. The Downpipes
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      07-11-2011, 08:51 AM   #4
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Quote:
Originally Posted by 330iSB View Post
are you sure its backfiring and not just the "gurgling and popping"? I have full catless and I get lots of gurgling and popping but they only time i ever get a hint of backfire is when i am wot at low rpm and then shift gears before 3500 or so

Heck! My N54 exhaust is all stock and it also gurgling and pops! I love it though. I think plenty of V-Max runs on the Autobahn helped in reaming out my exhaust pipes. lol I know lots of people are surprised when I tell them my exhaust is all stock!

OP - I bet you re-used your old exhaust gaskets. Most backfiring or severe popping comes from an exhaust leak upstream. A true back fire would mean your engine is running super lean. I bet its your old (leaking) exhaust gaskets.

Have a helper take some rags and hold them against the exhaust tips while the engine is running. Then YOU can go under the car (while its jacked up and on jack stands!!) and check for leaks. I bets its those exhaust gaskets at the downpipe/main cats to mid pipe flange. They take an awlfull amount of heat and are prone to be "one time" gaskets. It could also be further back at the muffler too.

Good Luck,
Dackel
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      07-11-2011, 01:21 PM   #5
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Quote:
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?
You are hearing some popping, which is totally normal. The same noises are present stock, just much harder to hear. When you remove two of the cats, the noise is amplified and you can actually hear it.

To get REAL backfire (flames out the exhaust tips), you'd need to be completely catless.
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      07-11-2011, 04:51 PM   #6
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N54 Backfiring
is awesome.

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      07-11-2011, 07:10 PM   #7
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Quote:
Originally Posted by Dackelone View Post
Quote:
Originally Posted by 330iSB View Post
are you sure its backfiring and not just the "gurgling and popping"? I have full catless and I get lots of gurgling and popping but they only time i ever get a hint of backfire is when i am wot at low rpm and then shift gears before 3500 or so

Heck! My N54 exhaust is all stock and it also gurgling and pops! I love it though. I think plenty of V-Max runs on the Autobahn helped in reaming out my exhaust pipes. lol I know lots of people are surprised when I tell them my exhaust is all stock!

OP - I bet you re-used your old exhaust gaskets. Most backfiring or severe popping comes from an exhaust leak upstream. A true back fire would mean your engine is running super lean. I bet its your old (leaking) exhaust gaskets.

Have a helper take some rags and hold them against the exhaust tips while the engine is running. Then YOU can go under the car (while its jacked up and on jack stands!!) and check for leaks. I bets its those exhaust gaskets at the downpipe/main cats to mid pipe flange. They take an awlfull amount of heat and are prone to be "one time" gaskets. It could also be further back at the muffler too.

Good Luck,
Dackel
Backfires come from a rich mixture, Dackel. My old STi would make really loud backfires between shifts as the AFR's would dip towards the richer side of the scale for it's cooling benefits.
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      07-11-2011, 07:15 PM   #8
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It's unburned fuel detonating in the exhaust because the exhaust is so hot it causes it to ignite. They're not massive explosions because only a little unburned fuel gets there.
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      07-11-2011, 07:16 PM   #9
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Quote:
Originally Posted by IGoFast1589 View Post
Backfires come from a rich mixture, Dackel...

That is a myth - I believe.

I have had some tuning experience with SW tuning (on Volkswagens and Porsche's)many years back, in the early 1990's. Most of the time a popping back fire is from running too lean a fuel mixture. I know common sense says its must be too rich of a mixture... but it is more common for it to be from a lean mixture.

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      07-11-2011, 07:19 PM   #10
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I apologize for the third post, but I can't modify a previous one from my phone. Dackel can be right about the gasket though, it's worth looking at. Also, I hope you have some sort of aftermarket tune with that downpipe otherwise I bet you that's your problem right there and you'd better fix that situation ASAP.
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      07-11-2011, 07:21 PM   #11
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Quote:
Originally Posted by Dackelone View Post
Quote:
Originally Posted by IGoFast1589 View Post
Backfires come from a rich mixture, Dackel...

That is a myth - I believe.

I have had some tuning experience with SW tuning (on Volkswagens and Porsche's)many years back, in the early 1990's. Most of the time a popping back fire is from running too lean a fuel mixture. I know common sense says its must be too rich of a mixture... but it is more common for it to be from a lean mixture.

Dackel
I believe you, I know it happens from a rich mixture but if it's coming from a lean one then that's a real issue. I don't really see logically how that works but I know you know what you're saying. Just adding my input to the conversation.
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      07-11-2011, 07:25 PM   #12
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No myth, Dackel. It has it's benefits, but the downsides are clearly minimally worse gas mileage and your not making as much power as you can that way. Although I would argue reliability over peak HP any day. Too many factors that go into ECU tuning for this topic right now.
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      07-11-2011, 07:25 PM   #13
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You guys are all wrong. It can't be a backfire because backfires come back through the intake manifold.

It may be an afterfire though...

:nerd:


OP you're probably confusing the burble and gurgle with an afterfire

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      07-11-2011, 07:30 PM   #14
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Quote:
Originally Posted by BrokenVert View Post
You guys are all wrong. It can't be a backfire because backfires come back through the intake manifold.

It may be an afterfire though...

:nerd:


OP you're probably confusing the burble and gurgle with an afterfire

Ok, you win by default. Myself and many others have all called it that forever. I guess it's like breaking a bad speech habit. Lol
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      07-11-2011, 08:49 PM   #15
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Quote:
Originally Posted by IGoFast1589 View Post
I apologize for the third post, but I can't modify a previous one from my phone. Dackel can be right about the gasket though, it's worth looking at. Also, I hope you have some sort of aftermarket tune with that downpipe otherwise I bet you that's your problem right there and you'd better fix that situation ASAP.
Hi. I'm running dinan stage 2, but it's a catless/resonatorless CP-e midpipes. Still stock midpipes (for now).

HPF intercooler coming soon! Woooo hoooo
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      07-11-2011, 08:55 PM   #16
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Quote:
Originally Posted by BrokenVert View Post
You guys are all wrong. It can't be a backfire because backfires come back through the intake manifold.

It may be an afterfire though...

:nerd:


OP you're probably confusing the burble and gurgle with an afterfire

Hi. If you call it gurgle then in confused. It's louder than my straightpipe exhaust civic ever was, happens in first gear (auto tranny) when shifting into 2nd. I'll go take a startup vid and post.
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      07-11-2011, 09:15 PM   #17
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k, so don't get me wrong, I downshift just to hear the burble/gurgle...love it!

First gear, WOT, when it shifts to 2nd it's not a gorgeous sound...big pop/bang noise.

Here's a startup video, I'll ask the GF to help out with a WOT run in 1st tomorrow.



Anyone else notice my exhaust starts to glow blue? lol!
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      07-12-2011, 01:38 AM   #18
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I love that sound. I used to roll down my windows every morning no matter how cold it is just to hear the "gurgle"
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      07-12-2011, 06:15 AM   #19
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Quote:
Originally Posted by evilstib View Post
Quote:
Originally Posted by IGoFast1589 View Post
I apologize for the third post, but I can't modify a previous one from my phone. Dackel can be right about the gasket though, it's worth looking at. Also, I hope you have some sort of aftermarket tune with that downpipe otherwise I bet you that's your problem right there and you'd better fix that situation ASAP.
Hi. I'm running dinan stage 2, but it's a catless/resonatorless CP-e midpipes. Still stock midpipes (for now).

HPF intercooler coming soon! Woooo hoooo
You are catless and without a resonator and you still asked the main question? Lol
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      07-12-2011, 08:01 PM   #20
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Quote:
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.
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      07-13-2011, 07:36 AM   #21
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Quote:
Originally Posted by IGoFast1589 View Post
You are catless and without a resonator and you still asked the main question? Lol
I'm not catless...N54 had 4 cats stock... I still have 2...Also shouldn't get loud popping/bang noises at the top of the RPM range when the tranny shifts...
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      02-04-2013, 04:20 PM   #22
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this is normal when removing cats and happens with my 6MT all the time, i love it. op isnt talking about the "gurgle" its an actual POP. heres a video. (this particular car is FBO, RB turbos and meth but i produce the same sound FBO, stock turbos and no meth)

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Last edited by comacow02; 02-04-2013 at 04:38 PM.
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