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Old 07-17-2002, 04:40 PM   #1
Reciprocity
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Question Exhaust pop, 98-99 vs 00 and up

Just curious here...

I've been thinking about the exhaust "pop" that we all seem to experience. From my understanding (and I could be TOTALLY wrong here) it is due to unburnt fuel hitting the hot cat and exploding.

Now...I'm having trouble thinking here but... When a car is running "rich" is that MORE fuel/LESS air than stoich or the other way around?

'Cause I was thinking...again from memory here...the 98s (and possibly the 99s) tend to run LEAN after putting on an aftermarket intake. Now do people with that lean effect experience the same amount of "popping" that us with 00 (which tend to run RICH after an aftermarket intake)?

Throwing it out here...lemmie know what you think.

NC
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Old 07-17-2002, 05:17 PM   #2
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An answer to your fuel question.
Rich= less oxygen per part combustable fuel.
Parts air|| Parts fuel
Lean 18 : 1
> greater then condition
Stoich ~14.7 : 1
< less then condition
Rich 10 : 1


Someone with a catless setup would be of great help... Do you hear the distinctive "pop."

Oh and one more thing, we must consider the variable in header design. Equal length vs non-equal length. For instatnce do people with MRT "Y" headers experiance "pop."

I think it will be helpful to eliminate or more correctly identify each condition we experience from the setup on our cars so that we break down and ID what the cause is..

~Chaise

Last edited by scoobyguy; 07-23-2002 at 03:45 PM.
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Old 07-17-2002, 05:24 PM   #3
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Thanks for the info on rich vs lean.

I have an MRT setup (which is actually an "H" or really...an "A") and I get the pops all the time.

Someone going catless would be the best indicator if it is the cat's heat causing the pops, and would help narrow down the search for information.

NC
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Old 07-17-2002, 05:37 PM   #4
imprezadan
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If I'm not mistaken, the 99s only ran lean after 5500rpm and with an intake. The mass airflow sensor gets "confused" I think.
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Old 07-17-2002, 11:46 PM   #5
DanzBorin
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yeah, the MAF gets tricked due to vibrations...

It isn't really running lean.
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Old 07-18-2002, 12:46 AM   #6
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My car doesnt pop with the custom exhaust I just got... Only once, but I think it was cause it was a hot day (100), and the exhaust had just been welded and was still hot too I dont remember it poping either when I tried reving it without a muffler at all awhile ago... (I couldnt resist!!!)

But, all the newer Imprezas I hear pop ALOT with exhaust mods! Especially your car Niel
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Old 07-18-2002, 03:57 PM   #7
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MY00, I had pop with the stock system, and I either have MORE pop or more NOTICABLE pop with the MRT system. I can get it to not pop by changing how I shift, but I'm not always that concerned. Until I take apart my system to fix the exhaust leak and find out my cat is falling apart like someones...

short term fuel trim is 0%
Long term fuel trim is +2% (was +4% before the exhaust leak).
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Old 07-18-2002, 04:31 PM   #8
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I have borla header and catback, and I get some LOUD pops. It seems more recently though, since I had my ECU flashed after the last recall...but that could just be my imagination. I did hit a nasty bump, and my 2nd cat shield got scrapped....if my 2nd cat got damaged would this cause more popping?
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Old 07-18-2002, 08:33 PM   #9
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I have intake and full borla exhaust / headers. My exhaust only seems to pop a lot between 2000 and 3000 rpm.
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Old 07-18-2002, 11:38 PM   #10
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I only have magnaflow muffler,but it pops like crazy. I love it!
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Old 07-23-2002, 03:53 PM   #11
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Hey have some more info about my own pop problems.... I threw a code about 4 days ago, sorry don't know what code dont have a scanner yet, and the "poping" is now more frequent. I guess I need to check to see if its a CEL issue or not.

However, I think we can get some insight I one of you without a cat can pipe in an let us know if you have "pops".



~Chaise


P.S Sorry for the stupid pun.
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Old 07-23-2002, 07:42 PM   #12
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Hey,
I have Borla headers, no cats or resonator out to the scoobysport backbox and i do experiance the "Pops" I still tend to run rich with my intake...but i hope that when I replace my bad front O2 sensor it should clear up...its funny that even with an s-afc i just can't tune away my rich condition.

-Terry
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Old 07-23-2002, 07:47 PM   #13
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Quote:
Originally posted by tmaler13
Hey,
I have Borla headers, no cats or resonator out to the scoobysport backbox and i do experiance the "Pops" I still tend to run rich with my intake...but i hope that when I replace my bad front O2 sensor it should clear up...its funny that even with an s-afc i just can't tune away my rich condition.

-Terry
no cats, no resonator? So it's just Borla header...a long pipe...then scoobysport can?

If you are still getting pops then it's not the gasses hitting the cat. Hmmmmm....

Are your pipes coated at all? wrapped?

I had forgotten about this thread!

NC
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Old 07-23-2002, 10:54 PM   #14
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Yes..thats correct, just headers...no wraps or coating, long pipe and the scoobysport. It sounds just like the WRC car. I think this may be solved by getting the o2 sensor fixed. Its just weird i figured that i could control it with my s-afc but i can't...it always seems to be rich and i still get the bad cat too rich sulpher smell.
my egt at wot and cruising stays at 1350 or less no matter how i tune the afc.
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Old 07-23-2002, 11:30 PM   #15
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I just noticed this today.

Have you guys, who hear exhaust pops, tried bogging down to engine in first? Drive really slow in first gear and let off the gas. (Clutch has to be fully engauged) I ususally do this in the parking garage at work. (5mph limit) When I let off the gas, I can hear the exhaust pop multiple times. It's not as loud as the pops I hear when shifting gears, but its there.
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Old 07-24-2002, 04:16 AM   #16
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my car pops like frickin mad. MRT replica headers, Blitz can. The only time it pops is when I get off, then back on the throttle. At which point my standable o2 meter spikes to rich, then goes back to normal. The pop always coincides with this rich spike.

Don
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Old 07-24-2002, 03:43 PM   #17
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So can we all agree to rule out cat vs no cat theory??


Let me assume for a minute that the pops are consistent for a rich condition in ever case. Then what we are hearing is unburnt fuel ingniting some where in the exhaust system. I don't see how this could be a good thing.


hmmm... need to get monitoring system installed.


Is there anyone who does not experience this "pop" condition?




~Chaise
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Old 07-24-2002, 04:20 PM   #18
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Not cats then...it must be header? Those pipes get VERY hot...and the sound would resonate throught he entire exhuast system?
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Old 07-24-2002, 05:27 PM   #19
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I didn't read the whole thread, but couldn't that popping be from when the exhaust gases from the two sides of the engine meet eachother?
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Old 07-25-2002, 12:19 AM   #20
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my my98 rs has the popping sound when i let off of it a bit then on it again.

From it back firing it blew the guts out of my random tech cat, so i removed it and guted it the rest of the way becasue it was ratting like crazy.

And i still get the popping sound yet but its louder because of just goin in a empty cat and echoing (sp?)

~Jeff

PS forgot to metion borla header, ramdom tech cat and 5ziegn cat back. ohh and i'm an auto too
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Old 07-25-2002, 12:55 AM   #21
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I have had a stock intake for 3 years. My car always runs rich. I have a Borla exhaust. I have upgraded my intake since and I still run rich. My car is MY99.
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