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New owner of an 05 OBW 5MT with 178K miles without any modifications. Pretty clean car that had the engine rebuilt at around 130K by a dealership mechanic shortly after the previous owner purchased the vehicle. PO kept detailed records of all maintenance providing them to me when I purchased the car. The car has spent all of it's life in SE VA so corrosion is minimal. Growing up in Cleveland, this would be the cleanest undercarriage that I have seen on a 13 year old car.



A week after purchasing a P2096 POST CATALYST FUEL TRIM SYSTEM TOO LEAN (BANK 1) code appeared so I purchased a WiFi code reader to clear and monitor but a few weeks later it would reappear. No other indications of a poor running vehicle. What I have read is that there could be around 357 different causes for that code but since I don't need an emissions check and my safety inspection wasn't due for a few months I figured I would just ride it out and reset it before the inspection.



A few weeks ago I notice that there was a lack of power with the car not revving past 4000 RPM and slow getting there despite the pedal being to the floor (yes I checked to see if the floormat was interfering with the pedal!). I'm a slow old man driver however the acceleration is too slow for my driving style to the point of being dangerous.



Changed air filter, check the intake boxes/hoses for clogs but it was clear. Sprayed the MAF and TB without change. The cats were replaced at 155k miles by PO. The ground cables that I could locate all appear in great condition with most of them looking newish. No underhood fuel filter.



Using TORQUE : Vacuum at idle is 18.5 and ~0 at WOT. Throttle position indicates 16.5 at idle and 77.8 WOT. Apparently it is common to only indicate 77.8 at WOT due to how the program calculates the position.



I do not want to guess that a cat is clogged as there are 3 with 2 of them being connected by a single pipe on drivers side. The parts for that guess would be ~$700. Just learned that I have a Super Low Emission Vehicle based on the 3 cats. The Walker components specify automatic transmission while the Magnaflow doesn't specify a transmission.



What am I missing and what else can I try before ordering cats?
 

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2001 VDC/SC One of a Kind
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The 2096 code was your indication of a problem and has probably contributed to other issues, or this is just something that came up on its own. I would suggest that you check the flow on the exhaust for possible clogged cat. Another series of things to check is the battery ampere output, and the ground conductance to the engine. You can't see inside the insulation and a conductance test will verify good/bad grounding. When you checked the data, did you happen to notice fuel trims? Floooring the accelerator changes the fuel map to open loop and the data from the AF and O2 sensors will be necessary for determination of fueling, but at idle and cruising the STFT and LTFT will allow us to see what the ECM is doing. You may also want to check fuel pressure.
 

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Discussion Starter #3
Thanks for the feedback.

How do I check for a clogged cat with the 3 cat system (U6)? The easiest one I guess will be the rear one as I can disconnect the passenger side pipe directly in front of it and shine a light through it but the front cats are located in the middle of the pipe.

Not scientific by any means but I did feel the exhaust flow coming out of the mufflers on the 05 with my 14 Forrester. The flow out of the Outback seems minimal even under throttle compared to the Forrester at idle.

Does anyone have a recommendation for exhaust components? Magnaflow and Walker seem to be the 2 name brands available.

Thanks
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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You can also pull the upstream O2 sensors (temporarily) and if it runs/breaths better, you have a decent case for pulling the cats and having a look.
 

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The replacement cats have been ordered. Since I will have to remove the O2 sensors for the swap, pull the upstream ones first before removing the exhaust to see if there is any difference.

Ended up going with Walker parts from AutoZone. With the 10% military discount, parts within two days, and several $60 AutoZone gift cards for $50 via Kroger it ended up being the best option.

After the work is done hopefully I will post that it was a success.
 

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Still waiting on a couple gaskets to arrive but I did remove the cats. The removal process was straight forward with 4 out of 5 O2 sensors came out without a problem. Only 10 bolts total holding it all together and only 2 were completed rusted but that was between the right cat and rear cat so those two didn't need to be removed.

There was a rattle in the rear cat. While looking on the tail end of it you can see a solid gauze type ball of material moving and blocking the exit. I'm going to guess that this was actually causing the blockage.

The remaining gaskets should be in by time I leave work so everything should go back together later today. Hopefully the rain holds out.
 
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