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2002 OBS, 2.5L N/A
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5 Posts
Discussion Starter · #1 ·
Hello all,

This question is about my 2002 Outback Sport, 2.5L 5-speed -

I just finished a new exhaust installation - Borla header, new OEM cat with new O2 sensors, and a Stromung catback midpipe/muffler. Reset computer - battery disconnected during install, idled around 20-25 minutes after restart, then shutoff before taking a 'spirited' drive. While driving, I experienced a few backfires when lifting the throttle for a shift. The backfire wasn't consistent, just a half-dozen times during a 20 minute drive. I stopped for a snack once, then resumed the trip home. A few more backfires occurred - all total I drove about 10-12 miles.

Will the ECU continue to learn the new status of my engine? Perhaps it will take a while to settle in? But, thought I would go ahead and pose the question to the experts.

My new cat was furnished by Subaru, after getting a CEL for the P0420 code. The CEL flashed on and off a dozen times or so before having the cat replaced (dealer installed, with new O2 sensors at my request/expense), then I was code-free for a thousand miles or so before replacing the exhaust.

The car has about 68k miles; I'm the second owner since 65k miles; previous owner said the plugs were replaced once, but I suppose I'll get some new ones to see if they have any effect.

What say you all - prayers? advice?

Can anyone recommend an Impreza tuner in the Atlanta, GA area for diagnosis? Should I give the car more miles to see if a code flashes?

Thanks,
John Sellers
 

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03 WRX wagon
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4,033 Posts
Its totally normal, and totally fine. My RS did the same thing with Borlas / high flow exhaust. I could actually control them and make it backfire on command haha, but don't worry about it. My WRX does it alot too, 3" catless turboback.
 

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Boxer rumble FTW!
2005 Subaru Impreza 2.5 RS
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621 Posts
how loud is it??? is it a pop or or loud explosive backfire? i have the same exhaust mods as you with a hfc pipe and mine pops loudy after accel and sometimes on decel but its due to the higher flowing exhaust pulses and the rich unburnt fuel popping in the exhaust, pretty normal for our cars, and won't hurt anything. only way to fix is to put stock bits back on.
 

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un-Banned by RS25.com
2000 SRP 2.5RS Coupe
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2,164 Posts
To get rid of the P0420 you have to heat wrap the headers and put in 02 sensor spacers.

Running your car with a CEL on will hurt your performance and mileage drastically.
 

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Boxer rumble FTW!
2005 Subaru Impreza 2.5 RS
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621 Posts
To get rid of the P0420 you have to heat wrap the headers and put in 02 sensor spacers.

Running your car with a CEL on will hurt your performance and mileage drastically.
possible but not drastically. not trying to be a dick here but the ECU see's the same o2s signals from the rear o2s before and after the code is tripped, so it will run the same as long as the o2s readings are not off enough to set the ecu into limp mode. but having the CEL on for this will not affect peformance or milage. i notice no change in having mine disabled now and driving with it on for the last eight months prior. but is nice not to look at it and have my cruise control back.
 

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2003 rs2.5 BRP
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831 Posts
you should reset your ecu after you do mods like that.

gives your car a chance to re-learn whats up with your driving in relation to your modifications and such.
 

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un-Banned by RS25.com
2000 SRP 2.5RS Coupe
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2,164 Posts
possible but not drastically. not trying to be a dick here but the ECU see's the same o2s signals from the rear o2s before and after the code is tripped, so it will run the same as long as the o2s readings are not off enough to set the ecu into limp mode. but having the CEL on for this will not affect peformance or milage. i notice no change in having mine disabled now and driving with it on for the last eight months prior. but is nice not to look at it and have my cruise control back.
I had a CEL on for a faulty knock sensor and my car bogged like shit. I had a 50% decline in MPG as well.
 

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Registered
2002 OBS, 2.5L N/A
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5 Posts
Discussion Starter · #9 ·
how loud is it??? is it a pop or or loud explosive backfire?
It's not a large backfire - just a little pop. I've owned a car before that could backfire explosively, it was even controllable but not good for the vehicle. I'm not too concerned with this small backfire the Subaru is presenting, especially since it may cease after the ECU bones up a bit about the new exhaust.

To get rid of the P0420 you have to heat wrap the headers and put in 02 sensor spacers.

Running your car with a CEL on will hurt your performance and mileage drastically.
I had my Borla header coated at a metallurgy shop - specifically to keep heat in for the catalytic converter efficiency.

You didn't read my initial post - I don't have the CEL/P0420 code anymore with the new OEM converter.

you should reset your ecu after you do mods like that.

gives your car a chance to re-learn whats up with your driving in relation to your modifications and such.
You didn't read my post either - I did reset the ECU. But, perhaps it's still in process of learning the new setup. Hopefully the backfires will go away.

Thanks all for the replies,
John Sellers
 

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00 2.5RS BRP
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687 Posts
you should reset your ecu after you do mods like that.

gives your car a chance to re-learn whats up with your driving in relation to your modifications and such.

did you read the part about "reseting the computer"

and ya mine backfires every now and then

gets pretty loud!!!
 

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Boxer rumble FTW!
2005 Subaru Impreza 2.5 RS
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621 Posts
I had a CEL on for a faulty knock sensor and my car bogged like shit. I had a 50% decline in MPG as well.

yeah that is to be expected from the knock sensor it can/will retard timing if it senses any pinging or detonation, or if the sensor or wiring to it are faulty will do the same. o2 sensor or rather the p0420 (cat ineffecieny code) is diffirent then this is is just comparing the front o2 to the rear o2 and looking for a similiar reading thus setting the p0420.
 

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03 PSM 2.5rs(totaled) :(
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16 Posts
Yesterday morning mine did this about 3 times! >:] ... I have had Borla Replica headers and just added a Stromung single-tip axleback.
 

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201 Posts
My car pops/backfires ALL the time. If I shift slow @ around 2500rpm it is really loud. When I let off the gas and my rpm is below or around 3500 it 'backfires'(or missfires? Idk wtf is with all these different 'fires'). I have a 3inch exhaust which obviously, is too big but what are you gonna do you know??!? It was free!

I am putting on my Borla Reps this week hopefully(I have had them in my closest for like 4 months now).

I really like the pop/backfire w/e..as long as it is not hurting my car(?) then it's all good.
 

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04 Mini Cooper S
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467 Posts
Mine does the same. Its normal. Probably because the borla UELs the gasses coming out at different rates. But i can control them to so i like it haha! I can scare little kids in town.
 

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The Silverback Mod
05 Black OBS
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8,896 Posts
you should reset your ecu after you do mods like that.

gives your car a chance to re-learn whats up with your driving in relation to your modifications and such.
Did you read the OP's post??? "disconnected the battery... let idle for 20-25 minutes" What do you call that! :help:
 

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MY02 White TS
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299 Posts
With my borla UEL+Stromung catback, I can sometimes hear a pop if I accelerate and let go of gas and the rpm drops quickly. But it sounds like it's coming from under my seat, like where the cat is. Also it feels like the pipes were being bent.

Is this what you guys mean by backfire?
 

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05' Impreza 2.5rs, CGM
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1,967 Posts
small subaru backfires make me giddy! HAHA :) :D

Its nothing to worry about. my neighbors WRX backfires all the time. Little pops here and there. He also has an axleback scoobysport, with the scoobysport uppipe and downpipe on his car, and his own custom flash.

He has never had a single problem and his car has been like that for the last 20k mikes!
 

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1999 ver7 coupe
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504 Posts
Almost all engines will pop and blow flames into the exhaust once they are warmed up. The stock exhaust system is designed to suppress these pulses.

Some engines are worse than others though...I took an RX8 out for a test drive and you could hear the heavily muffled backfires each time you got off the throttle. Faintly, but it was still doing it as stock.
 
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