2001 Subaru Legacy Outback Exhaust

[maroon_subi]

Hey everyone.

 

I have a 01 Legacy Outback sedan that I just replaced the entire exhaust. The header is Emusa brand with unequal lengths. The shop only put one cat on and a Flowmaster muffler. I believe the pipe width is either 2.25'' or 2.5". The car has an awesome deep sound until you get to the muffler, and then it RATTLES. I took it back to the shop to have the hangers checked and they told me that the rattle was from so much air flow and that a resonator would help with the rattle. The real reason I had the exhaust replaced was because the Check Engine light came on, and Advanced said that it was either a bad cat or O2 sensor. The muffler shop told me that my O2 sensors were fine, and like I said, they replaced one of the Cats and deleted the other BUT when I had them check the computer, they said that Subaru's require 2 cats. My check engine light came back on after the reset and now it is shaking like crazy at stops with the car in Drive.

 

Three questions:

1. What will get the rattle out of my exhaust?

2. Does Subaru require 2 Cats or do I need to replace my O2s?

3. How do I fix the shaking at stops with the car in drive?

 

I am including the link for the Header so that you all can see exactly what I bought.

http://www.speedyracer.com/headers/exhaust-parts/headers/1999-2005-SUBARU-IMPREZA-25L-RS-SOHC-HEADER-STAINLESS

 

I have not gotten to do a lot of maintenance to the car yet. (I got excited with Income Tax, I know.)

I have replaced the following:

 

Air filter

Cabin air filter

PCV valve

Fuel Filter (Octane Booster also)

Synthetic Oil Change

[screwbaru2]

Seems to me if your car requires 2 cats then the ECU is expecting signals from 3 O2 sensors (2 upstream and one downstream.  If it doesn't get those signals it is not going to run right at all.  I don't know if the ECU can be "fooled", I tend to doubt it.  Also if your car is designed to have 2 cats it will not pass inspection with one, at least as far as I know.

[matt167]

A 2001 does not use the downstream for anything except the Cel. But your headder might be fooling the upstreams

[maroon_subi]

So I need to put another cat on the car. Simple enough.

 

 

As far as the O2 sensors are concerned, what should I do to "unfool" them? Replace all of them? My husband and I could only find 2 O2's neither of which were on the old or new header. I am pretty sure that the exhaust is causing the issue with almost stalling at stops while in Drive.

 

I am not sure what the CEL is. Check Engine Light?

 

Would any of this fix the rattle in the muffler? I was thinking that sense the Flowmaster is elongated, the air was expanding and then having issues getting back into the end pipe. Would a cylindrical muffler fix the rattle?

[bakedpotatoechips99]

 It seems like screwbaru2 is giving you the right information as far as I can guess. At least he is right about the O2 sensors. For a temporary solution, at least until you get the other catalytic,

it might be possible to drill, tap and mount a downstream or upstream O2 sensor,

  and get it to run at least acceptably. It likely still would not pass emissions testing, either because by law 2 catalytic converters are required, or, because the emissions would be

 above allowed limits. I can't say for sure. 

  This MIGHT get it running well enough to use the car, at least until until you can install another converter, etc.

 . That header looks really nice, chromed and high quality. The rattle could be the baffle inside of the muffler came loose or broke. But who knows for sure.

[Bushwick]

CEL is probably the header. Factory might run dual cats, but a single cat can suffice so long as it's a decent diameter and not too far away from the header (further away, the colder it'll operate).

 

Link states header uses factory O2 locations. Your down stream O2 MUST be AFTER the cat. Verify that it is.

 

 

The vibration is most likely a rubbing exhaust pipe, rubbing muffler, etc. If ANY of the exhaust touches the body or anything solid, it'll vibrate and make noise. This is why the factory uses soft rubber hanger isolators is negate any vibration.

 

Sounds like the muffler shop did a poor fitment. They are absolutely bull-sxxxing you about the increased flow causing extra vibrations, or the person is a moron. You can run 2" or 3" pipe, it won't cause extra vibrations. An obnoxious 40 series Flowmaster (or similar) however can cause excessive droning and that can cause a resonance vibration in the car, or make other objects vibrate.

[idosubaru]

***** The first thing we need to know is the current check engine light code.  Have it read and post it here.  Don't post the diagnosis or what someone says the code means - give us the exact code. 

P0420 is the catalyst inefficiency code that usually starts debacles like this.  I'll assume that's the issue, but definitely post the code here.  

 

1. the rattle - i'm uncertain about that.   seems like the shop should fix it but "fix it" might mean a whole new muffler/system $$$$ if you annoy them and they're not wanting to diagnose/address. 

 

2. for the Check Engine light - you only need one converter.  the system doesn't check catalyst efficiency until the car is up to operating temps.  

second converter functions when warm.  the first converter is a pre-converter and intended to mitigate emissions during the warm up period - when the O2 sensors are not even in use yet. 

 

so it depends how you look at it. 

 

A.  the system was designed with two converters - a preconverter for warm up period, one for nominal ops.  but both are not "needed" at all.  the car was "designed" with perfect clear coat - it probably doesn't have that either.  

B.  the computer/check engine light/emissions only require one converter to work properly - the rear one. 

 

on stock systems installing a $5 spacer between the rear O2 sensor and the exhaust often gets rid of the check engine light.  easy, cheap, and it sometimes works.  i dont' know what's going on here with all the noise, custom exhaust, etc - but for $5 and a few minutes it would take on a new exhaust (no rust), i'd install one of those immediately.  this issue is so common i've got a pile of those extenders in my garage. 

 

a simple way to test if exhaust is causing issues or not is to disconnect the exhaust manifold from the engine and take a drive. 

 

if the issue goes away - it's the exhaust

if the issues don't go away - it's not the exhaust. 

 

exhaust should not cause any issues at all unless it's clogged.

 

vibration in drive at stop is usually due to aftermarket front CV shafts.  replace the offending axle.  always use Subaru axles (green inner cups).  reboot and they always last the life of the vehicle.  replacement is a waste and problematic. 

get a used one from www.car-part.com and reboot it with Subaru boots. 

[maroon_subi]

I just had Advanced Auto check my computer. The code that pulled up was indeed P0420. The computer said something about "bank 1". The gentleman said my O2s were working, otherwise the system wouldnt show up. He also stated that the rattle in the muffler could be some left over metal parts from something.

 

Im going to try and disconnect the.exhaust manifold tommorrow and see what happens. I am also going to go to a different shop and have.them.test that cat again. It could be possible the cat is a no go and I didnt watch the original shop check it.

 

Should I take it back to the muffler shop or go to a different one?

[maroon_subi]

Edit ​

Edited April 6, 2016 by maroon_subi

[maroon_subi]

 

***** The first thing we need to know is the current check engine light code.  Have it read and post it here.  Don't post the diagnosis or what someone says the code means - give us the exact code. 

P0420 is the catalyst inefficiency code that usually starts debacles like this.  I'll assume that's the issue, but definitely post the code here.  

 

1. the rattle - i'm uncertain about that.   seems like the shop should fix it but "fix it" might mean a whole new muffler/system $$$$ if you annoy them and they're not wanting to diagnose/address. 

 

2. for the Check Engine light - you only need one converter.  the system doesn't check catalyst efficiency until the car is up to operating temps.  

second converter functions when warm.  the first converter is a pre-converter and intended to mitigate emissions during the warm up period - when the O2 sensors are not even in use yet. 

 

so it depends how you look at it. 

 

A.  the system was designed with two converters - a preconverter for warm up period, one for nominal ops.  but both are not "needed" at all.  the car was "designed" with perfect clear coat - it probably doesn't have that either.  

B.  the computer/check engine light/emissions only require one converter to work properly - the rear one. 

 

on stock systems installing a $5 spacer between the rear O2 sensor and the exhaust often gets rid of the check engine light.  easy, cheap, and it sometimes works.  i dont' know what's going on here with all the noise, custom exhaust, etc - but for $5 and a few minutes it would take on a new exhaust (no rust), i'd install one of those immediately.  this issue is so common i've got a pile of those extenders in my garage. 

 

a simple way to test if exhaust is causing issues or not is to disconnect the exhaust manifold from the engine and take a drive. 

 

if the issue goes away - it's the exhaust

if the issues don't go away - it's not the exhaust. 

 

exhaust should not cause any issues at all unless it's clogged.

 

vibration in drive at stop is usually due to aftermarket front CV shafts.  replace the offending axle.  always use Subaru axles (green inner cups).  reboot and they always last the life of the vehicle.  replacement is a waste and problematic. 

get a used one from www.car-part.com and reboot it with Subaru boots. 

 

The Vibration/Surging/Revving did not happen until after I replaced the Exhaust. It happened again on my way home, so I checked the RPM gauge and nothing was moving. The engine sounds and the car feels like it is revving, similar to when you are on a hill in a 5 speed and press the gas to keep from going backwards. The sensation is in short bursts. It will do it for maybe a couple of seconds the quit and continue on  that way.

 

I had the axles replaced by a Subaru shop a couple of months ago though.