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Old 05-17-2013, 01:02 AM   #1
Jubert69
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Default Swapped Downpipes, Screwed up my AFR?

Hey guys,

I recently switch downpipes both catless because of fitment issues with the first one. No size difference.

The only thing that really changed was the location of the Wideband. It went from the side of the downpipe (4-6 inches from the turbo) to the top of the stream. So it went from the actual sensor catching the stream from the side to top of the pipe so in essence it's pointing to the ground.

The idling AFR went from 14.7-15.0 to 16.2-16.8. Normal driving it's the same stoich 14.7-15.0. I went into open loop fueling, and it was originally tuned for 11.2, and it was hitting 11.8-12.

I don't have a problem tuning it to the correct AFRs, I'm just worried my sensor is giving wrong readings. Or can a downpipe that is very similar really throw off AFR?
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Old 05-20-2013, 04:54 PM   #2
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Bump. Going to compare the stock wideband vs. the aftermarket wideband tomorrow when I get my tactrix cable back
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Old 05-20-2013, 08:39 PM   #3
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You will be comparing the stock narrowband to aftermarket wideband. Log your fuel trims.

Last edited by wgr73; 05-20-2013 at 08:56 PM. Reason: corrected! Mis-read
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Old 05-20-2013, 08:43 PM   #4
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The downpipe won't affect AFR, my guess is you introduced a leak while doing the swap.
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Old 05-21-2013, 12:24 PM   #5
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Quote:
Originally Posted by wgr73 View Post
You will be comparing the stock narrowband to aftermarket wideband. Log your fuel trims.
Stock wideband in the header for idle.

Quote:
Originally Posted by the suicidal eggroll View Post
The downpipe won't affect AFR, my guess is you introduced a leak while doing the swap.
That's what I thought, but I didn't even touch anything else. I didn't remove my IC to do the swap.
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Old 05-21-2013, 02:04 PM   #6
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Quote:
Originally Posted by Jubert69 View Post
Stock wideband in the header for idle.



That's what I thought, but I didn't even touch anything else. I didn't remove my IC to do the swap.
You could have an exhaust leak especially if you reused a gasket.
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Old 05-23-2013, 11:03 AM   #7
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^^ Gonna check for leaks.

I did plug in my tactrix cable and saw the stock WB was reading stoich at idle while the aftermarket WB was reading 16.2-16.8ish.. hmmm
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Old 05-23-2013, 05:01 PM   #8
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Stock O2 sensor is a narrowband, not a wideband sensor. It's common for manufacturers to use narrowband sensors since they're cheaper on average.
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Old 05-23-2013, 07:19 PM   #9
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Quote:
Originally Posted by projektdotnet View Post
Stock O2 sensor is a narrowband, not a wideband sensor. It's common for manufacturers to use narrowband sensors since they're cheaper on average.
The stock O2 is, and always has been a wideband sensor on our cars. Its measurements can't be trusted in boost because of the pressure in the uppipe, but that's not the sensor's fault.
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Old 05-23-2013, 07:40 PM   #10
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Quote:
Originally Posted by the suicidal eggroll View Post
The stock O2 is, and always has been a wideband sensor on our cars. Its measurements can't be trusted in boost because of the pressure in the uppipe, but that's not the sensor's fault.
I knew you would be along shortly to set the record straight Eggroll
Not too many folks on here can explain fueling any better than you.
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Old 05-23-2013, 08:17 PM   #11
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Quote:
Originally Posted by the suicidal eggroll View Post
The stock O2 is, and always has been a wideband sensor on our cars. Its measurements can't be trusted in boost because of the pressure in the uppipe, but that's not the sensor's fault.
My apologies, after your post I double checked and sure enough I was wrong, kudos. Is the rear O2 also a wideband or is that a narrowband? (I didn't realize there was one in the uppipe/header as well, I only knew of the one in the downpipe) It's been too long since I've been on the underside of the car.
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Old 05-23-2013, 11:06 PM   #12
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Quote:
Originally Posted by projektdotnet View Post
My apologies, after your post I double checked and sure enough I was wrong, kudos. Is the rear O2 also a wideband or is that a narrowband? (I didn't realize there was one in the uppipe/header as well, I only knew of the one in the downpipe) It's been too long since I've been on the underside of the car.
Downpipe = Narrowband
Header = Wideband
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Old 05-24-2013, 03:17 AM   #13
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Quote:
Originally Posted by Jubert69 View Post
Downpipe = Narrowband
Header = Wideband
Learning new things about Subarus all the time, thanks to you and suicidal eggroll for the info.
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Old 05-24-2013, 08:09 AM   #14
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So if you have a jdm twinscroll motor with the stock front o2 in the downpipe you can go by that?
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Old 05-24-2013, 09:24 AM   #15
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Quote:
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So if you have a jdm twinscroll motor with the stock front o2 in the downpipe you can go by that?
It will be more accurate then the one in the header on USDM cars. But for better accuracy aftermarket is needed.
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Old 05-24-2013, 10:08 AM   #16
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Originally Posted by endrswrd View Post
It will be more accurate then the one in the header on USDM cars. But for better accuracy aftermarket is needed.
^ this

Many people have moved the front O2 into the downpipe with good results. This does allow the sensor's readings to maintain accuracy into boost, however the sensor's rich limit of ~11.0 will still cause problems when trying to use it to tune.
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Old 05-24-2013, 11:47 AM   #17
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I have a aem uego wideband installed in the downpipe as well as stock, just wondering how close the stock one was to the Aem
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Old 05-25-2013, 02:48 AM   #18
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Just did a WOT pull, and my AFRs are rock solid since the last time I tuned it 11.0. Still scratching my head for the "lean" values during idle
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Old 05-25-2013, 10:51 AM   #19
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Quote:
Originally Posted by Jubert69 View Post
Just did a WOT pull, and my AFRs are rock solid since the last time I tuned it 11.0. Still scratching my head for the "lean" values during idle
I still think you have a minor exhaust leak (most likely at the downpipe). At idle or low cruise your wideband has less gas to measure and the leak would affect what makes it to your wideband . When you go into boost the volume of exhaust gas increases enough to overcome this.
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