Hopeful Soobie Posted June 8, 2020 Share Posted June 8, 2020 (edited) So im pulling a p0420. Deleted the midpipe cat (which I was told by the shop wasnt monitored anyway?) And deleted reso and mufflers, cus exhaust sound. Im still dealing with the 420 and its driving very sluggish and loss of power around 2k to 3k in 2nd and 3rd gears most noticeably. Im thinking the o2 is either bad or my up pipe or down pipe cats are bad. Either way im thinking about going catless. My issue - do I spend the money on a new o2 sensor to risk it going bad again? If I buy a new sensor and go catless, won't I will get the rough driving equal to the way it is now since the o2 sensor is trying to correct the af ratio since no cat? I tried the spark plug anti fouler with no luck. I mean... in my head a catless system has to have some kind of simulator or dummy o2 in order to not confuse the engine and run smoothly, right??? I've done a bunch of research and can't seem to quite find the answer I need. If anyone has input or has gone through this, please help out. Or if there is an answer from another forum or video that I've not yet discovered, share link? I've saved posting on here for a last resort as to not waste time. Also i have a cobb accessport. If that matters. Issue was long before the ap though. Love you guys you're the best! 2008 Lgt Sent from my SM-G975U using Tapatalk Edited June 8, 2020 by Hopeful Soobie Link to comment Share on other sites More sharing options...
Pleides Posted June 9, 2020 Share Posted June 9, 2020 First of all, catless exhausts smell terrible and are not great for the environment. At least consider having one so you aren't completely straight-piped. Have you tuned the car since doing any of this exhaust work? I'm talking taking the car to a respected tuning shop and having them look it over before putting it on the dyno. This is a turbo car and every little mod you make to the exhaust, intake, etc required a new tune. Link to comment Share on other sites More sharing options...
Max Capacity Posted June 9, 2020 Share Posted June 9, 2020 Replace the front O2 sensor with a Denzo. Put a catted Dp on and make sure the car is tuned for stage 2. https://legacygt.com/forums/showthread.php/idea-web-links-saved-various-parts-219238p5.html see post 172 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
NORULZleggy Posted June 9, 2020 Share Posted June 9, 2020 Yeah my cattless WRX smelled so bad The inside smelled like a track car lol. Link to comment Share on other sites More sharing options...
Infosecdad Posted June 9, 2020 Share Posted June 9, 2020 I have a highflow cat (HFC) in my downpipe and I actually added a second HFC to my 3" midpipe to almost eliminate the smell. Negligible performance impact from what I can tell. Link to comment Share on other sites More sharing options...
Max Capacity Posted June 9, 2020 Share Posted June 9, 2020 Yeah my cattless WRX smelled so bad The inside smelled like a track car lol. You young guys. When I was younger and started driving, cars didn't have cat's...how did we all get by... 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 10, 2020 Author Share Posted June 10, 2020 Replace the front O2 sensor with a Denzo. Put a catted Dp on and make sure the car is tuned for stage 2. https://legacygt.com/forums/showthread.php/idea-web-links-saved-various-parts-219238p5.html see post 172This link isn't working. I copied and pasted on Chrome and still no luck. I got my denso o2 in today. Sure hope it fixes the problem. If not ill look into getting a catted dp. Can't drive it right now as its on jacks awaiting brake parts. I'll have it done tomorrow. Any affordable options out there someone may recommend for the dp? And is any aftermarket catted dp compatible with stage 2? Right now I'm just running a stage 1 with my exhaust set up (straight piped after the downpipe) Also, this should definitely be my issue, right? In my head its either the o2 or the dp cat since the deleted cat wasn't monitored in the first place. Especially being the stock cat and o2 with 156k miles. But i get obsessive and research much, much too deeply. Im not trying to go crazy with mods. Just a fun daily. Maybe stage 2 eventually if not forced into it to fix this issue. Thanks guys. Sent from my SM-G975U using Tapatalk Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 10, 2020 Author Share Posted June 10, 2020 Sorry, another quick thought: Should I be concerned at all about the rear o2? Or is it irrelevant to this issue? Sent from my SM-G975U using Tapatalk Link to comment Share on other sites More sharing options...
Pleides Posted June 10, 2020 Share Posted June 10, 2020 Sorry, another quick thought: Should I be concerned at all about the rear o2? Or is it irrelevant to this issue? Sent from my SM-G975U using Tapatalk You can have your tuner tune the rear O2 out if you like, which would have to happen regardless if you decat the car. Link to comment Share on other sites More sharing options...
Max Capacity Posted June 10, 2020 Share Posted June 10, 2020 This link isn't working. I copied and pasted on Chrome and still no luck. I got my denso o2 in today. Sure hope it fixes the problem. If not ill look into getting a catted dp. Can't drive it right now as its on jacks awaiting brake parts. I'll have it done tomorrow. Any affordable options out there someone may recommend for the dp? And is any aftermarket catted dp compatible with stage 2? Right now I'm just running a stage 1 with my exhaust set up (straight piped after the downpipe) Also, this should definitely be my issue, right? In my head its either the o2 or the dp cat since the deleted cat wasn't monitored in the first place. Especially being the stock cat and o2 with 156k miles. But i get obsessive and research much, much too deeply. Im not trying to go crazy with mods. Just a fun daily. Maybe stage 2 eventually if not forced into it to fix this issue. Thanks guys. Sent from my SM-G975U using Tapatalk https://www.amazon.com/gp/product/B001F799X6/ Make sure you buy the correct sensor. The first link was the sticky that JmP6889928 has up top. See post 172 in that sticky 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 10, 2020 Author Share Posted June 10, 2020 https://www.oreillyauto.com/detail/b/denso-3367/engine-sensors---emissions-25132/engine-sensors-25049/oxygen-air-fuel-ratio-sensor-12041/b265c6634ee9/denso-air-fuel-sensor/2349035/4240189/2008/subaru/legacy?q=Denso+o2&pos=2 This is the o2 I picked up from oreilly. W ha ts the difference between this one and the one posted in the sticky? Sent from my SM-G975U using Tapatalk Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 10, 2020 Author Share Posted June 10, 2020 O2 didn't fox the problem. Guess my next step is to get a new dp? Amy suggestions? Sent from my SM-G975U using Tapatalk Link to comment Share on other sites More sharing options...
Max Capacity Posted June 10, 2020 Share Posted June 10, 2020 (edited) https://www.oreillyauto.com/detail/b/denso-3367/engine-sensors---emissions-25132/engine-sensors-25049/oxygen-air-fuel-ratio-sensor-12041/b265c6634ee9/denso-air-fuel-sensor/2349035/4240189/2008/subaru/legacy?q=Denso+o2&pos=2 This is the o2 I picked up from oreilly. W ha ts the difference between this one and the one posted in the sticky? Sent from my SM-G975U using Tapatalk Because we know that one works well in these cars. Here's a search I just did, for a 2008 Legacy GT, seems its the same one we all buy 234-9120. You did not buy the correct one. https://www.google.com/search?q=Denzo+O2+sensor+2008+Subaru+Legacy+GT&oq=Denzo+O2+sensor+2008+Subaru+Legacy+GT&aqs=chrome..69i57.22358j0j8&sourceid=chrome&ie=UTF-8 Edited June 10, 2020 by Max Capacity 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Max Capacity Posted June 10, 2020 Share Posted June 10, 2020 Just did this search, https://www.oreillyauto.com/search/2008/subaru/legacy?q=Denzo+234-9120 Looks like they don't know what fits these cars. Trust us, get the correct Denzo sensor for the front O2 on your car. We all know these work. I'm on my third one in 16 years. Most us with a custom tune have the rear sensor deleted. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 10, 2020 Author Share Posted June 10, 2020 Because we know that one works well in these cars. Here's a search I just did, for a 2008 Legacy GT, seems its the same one we all buy 234-9120. You did not buy the correct one. https://www.google.com/search?q=Denzo+O2+sensor+2008+Subaru+Legacy+GT&oq=Denzo+O2+sensor+2008+Subaru+Legacy+GT&aqs=chrome..69i57.22358j0j8&sourceid=chrome&ie=UTF-8Awesome! I'll order that one and return the one I got from oreilly. Really hope that does the trick. Also, I failed to mention my AF Learning get a bit crazy. I've seen it go upwards of +15 at the highest. I only have the issues when the car is up to temperature. Which, in my head, further confirms the o2 causing the problem. Does that sound right? Sent from my SM-G975U using Tapatalk Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 10, 2020 Author Share Posted June 10, 2020 Just did this search, https://www.oreillyauto.com/search/2008/subaru/legacy?q=Denzo+234-9120 Looks like they don't know what fits these cars. Trust us, get the correct Denzo sensor for the front O2 on your car. We all know these work. I'm on my third one in 16 years. Most us with a custom tune have the rear sensor deleted.Great thanks! Is the cobb stage 1 tune sufficient to delete the rear o2? Or should I keep it until/if I eventually go stage 2? Sent from my SM-G975U using Tapatalk Link to comment Share on other sites More sharing options...
Max Capacity Posted June 10, 2020 Share Posted June 10, 2020 To answer that question, hopefully one of the members that know that stuff will chime in. Spend some time reading other post and you'll find the guys you ask. Check out the Tuning Forum. Lot's of great people here. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Hopeful Soobie Posted June 11, 2020 Author Share Posted June 11, 2020 so i got the 234-9120 and the terminals dont fit... Link to comment Share on other sites More sharing options...
Max Capacity Posted June 12, 2020 Share Posted June 12, 2020 Someone must have done something to your car. These should all be the same. Can you follow the other cable...it should be right there in the right shock tower if I remember correctly. Does it look like its been messed with ? 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Max Capacity Posted June 12, 2020 Share Posted June 12, 2020 May be a picture or two ? 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
DaveWaters Posted June 12, 2020 Share Posted June 12, 2020 Did you buy that to replace upstream or down stream? That’s the upstream replacement. Screws into exhaust manifold plugs in at passengers side strut tower. Link to comment Share on other sites More sharing options...
Max Capacity Posted June 12, 2020 Share Posted June 12, 2020 P0420 Catalyst System Efficiency Below Threshold (Bank 1) That's the front one. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
DaveWaters Posted June 12, 2020 Share Posted June 12, 2020 Max- I’d think that would be the downstream one, no? Since it comes after cat and can tell if the cat is doing its job. The upstream is pre catalyst. Link to comment Share on other sites More sharing options...
Max Capacity Posted June 12, 2020 Share Posted June 12, 2020 Isn't bank 1 the front and Bank 2 the rear ? I know Bank 1 is also the passenger side of the engine. Here's the other codes P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1) P0132 O2 Sensor Circuit High Voltage (Bank 1 Sensor 1) P0133 O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) P0134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1) P0137 O2 Sensor Circuit Low Voltage (Bank Sensor 2) P0138 O2 Sensor Circuit High Voltage Bank 1 Sensor 2) P0139 O2 Sensor Circuit Slow Response Bank 1 Sensor 2) I'd assume sensor 2 is the rear. ? 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Max Capacity Posted June 12, 2020 Share Posted June 12, 2020 Found this in here, https://www.google.com/search?q=is+p0420+upstream+or+downstream&oq=Is++P0420&aqs=chrome.1.69i57j0l7.10477j0j8&sourceid=chrome&ie=UTF-8 Can a bad o2 sensor cause a p0420 code? If the rear O2 sensor is getting faulty values, the p0420 code will get stored in the engine control unit. It could be because the catalytic converter is defective, or a false alarm because one of the O2 sensors is damaged.Aug 17, 2019 That makes it clear. I was wrong thinking it was the front O2. Just have to ask Google. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
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